View source for Challenger Deep

{{Short description|Deepest known point of Earth's seabed}}
{{For|the book|Challenger Deep (novel){{!}}''Challenger Deep'' (novel)}}
{{Use dmy dates|date=March 2023}}
{{Infobox body of water
| name           = Challenger Deep
| oceans         = [[Pacific Ocean]]
| mapframe       = yes
| mapframe-zoom  = 1
| pushpin_map    = Earth
| max-depth      = {{cvt|10935|±|6|m|ft|0}} below sea level
| location       = [[Mariana Trench]]
| agency         = [[Federated States of Micronesia]]
}}
[[File:Marianatrenchmap.png|thumb|upright=1.3|Location of Challenger Deep within the [[Mariana Trench]] and western Pacific Ocean]]

The '''Challenger Deep''' is the [[List of submarine topographical features#List of oceanic trenches|deepest known point]] of the [[seabed]] of Earth, located in the western [[Pacific Ocean]] at the southern end of the [[Mariana Trench]], in the ocean territory of the [[Federated States of Micronesia]].

The [[General Bathymetric Chart of the Oceans|GEBCO]] Gazetteer of Undersea Feature Names indicates that the feature is situated at {{coord|11|22.4|N|142|35.5|E}} and has an approximated maximum depth of {{Convert|10,903 to 11,009|m|abbr=on}}<ref>{{Cite journal |last1=Loranger |first1=Scott |last2=Barclay |first2=David |last3=Buckingham |first3=Michael |date=2021-04-19 |title=Implosion in the Challenger Deep: Echo Sounding with the Shock Wave |url=https://tos.org/oceanography/article/implosion-in-the-challenger-deep-echo-sounding-with-the-shock-wave |journal=Oceanography |volume=34 |issue=2 |pages=156–165 |doi=10.5670/oceanog.2021.201 |access-date=2024-08-20 |doi-access=free|bibcode=2021Ocgpy..34b.201L |hdl=1912/27739 |hdl-access=free}}</ref> below sea level. A 2011 study placed the depth at {{cvt|10920|±|10|m|ft|0}}<ref name="GEBCO Gazetteer of Undersea Feature Names">{{Cite news|url=http://www.gebco.net/data_and_products/undersea_feature_names/#feature_links4|title=IHO-IOC GEBCO Gazetteer of Undersea Feature Names, August 2011 version|date=August 2011|publisher=GEBCO|access-date=20 March 2012|archive-date=6 November 2021|archive-url=https://web.archive.org/web/20211106222714/https://www.gebco.net/data_and_products/undersea_feature_names/#feature_links4|url-status=live}}</ref> with a 2021 study revising the value to {{cvt|10935|±|6|m|ft|0}} at a 95% [[confidence interval|confidence level]].<ref>{{Cite journal |last1=Greenaway |first1=Samuel F. |last2=Sullivan |first2=Kathryn D. |last3=Umfress |first3=S. Harper |last4=Beittel |first4=Alice B. |last5=Wagner |first5=Karl D. |date=2021-10-26 |title=Revised depth of the Challenger Deep from submersible transects; including a general method for precise, pressure-derived depths in the ocean |journal=Deep Sea Research Part I: Oceanographic Research Papers |volume=178 |article-number=103644 |doi=10.1016/j.dsr.2021.103644 |issn=0967-0637 |doi-access=free|bibcode=2021DSRI..17803644G}}</ref> 

The depression is named after the British [[Royal Navy]] survey ships {{HMS|Challenger|1858|6}}, whose [[Challenger expedition|expedition of 1872–1876]] first located it, and [[HMS Challenger (1931)|HMS ''Challenger II'']], whose expedition of 1950–1952 established its record-setting depth.<ref name=":1">{{Cite book |last=Gaskell |first=Thomas F |title=Under the Deep Oceans: Twentieth Century Voyages of Discovery |publisher=Eyre & Spottiswoode |year=1960 |location=London |pages=24–25}}</ref> The first descent by any vehicle was conducted by the [[United States Navy]] using the [[bathyscaphe]] ''[[Bathyscaphe Trieste|Trieste]]'' in January 1960. {{As of|2022|July}}, there were 27 [[list of people who descended to Challenger Deep|people who have descended to the Challenger Deep]].

==Topography==
[[File:Challenger Deep EM124 Sonar Map and Diving History 101119.jpg|thumb|upright=1.35|Sonar mapping of the Challenger Deep by the [[USNS Indomitable (T-AGOS-7)|DSSV ''Pressure Drop'']] employing a Kongsberg SIMRAD EM124 multibeam echosounder system (26 April – 4 May 2019)]]

The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped [[oceanic trench]], which itself is an unusually [[Hadal zone|deep feature]] in the ocean floor. The Challenger Deep consists of three basins, each {{convert|6|to|10|km|mi|1|abbr=on|lk=on}} long, {{convert|2|km|mi|1|abbr=on}} wide, and over {{convert|10850|m|ft|0|abbr=on}} in depth, oriented in echelon from west to east, separated by mounds between the basins {{convert|200|to|300|m|ft|abbr=on}} higher. The three basins feature extends about {{convert|48|km|mi|abbr=on}} west to east if measured at the {{convert|10650|m|ft|0|abbr=on}} [[isobath]].<ref>{{Cite journal |title=A precise bathymetric map of the world's deepest seafloor, Challenger Deep in the Mariana Trench |first1=Masao |last1=Nakanishi |first2=Jun |last2=Hashimoto |journal=Marine Geophysical Research |date=December 2011 |volume=32 |issue=4 |pages=455–63 |doi=10.1007/s11001-011-9134-0|bibcode=2011MarGR..32..455N |s2cid=55042876 |hdl=10069/25460 |hdl-access=free}}</ref> Both the western and eastern basins have recorded depths (by sonar bathymetry) in excess of {{convert|10920|m|ft|0|abbr=on}}, while the center basin is slightly less deep.<ref name="Stewart, Heather & Jamieson, Alan. (2019)"/> The closest land to the Challenger Deep is [[Fais Island]] (one of the outer islands of [[Yap]]), {{convert|287|km|mi|abbr=on}} southwest, and [[Guam]], {{convert|304|km|mi|abbr=on}} to the northeast.<ref>''[[The Colbert Report]]'', airdate 12 April 2012, interview with [[James Cameron]]</ref>
Detailed sonar mapping of the western, center and eastern basins in June 2020 by the [[USNS Indomitable (T-AGOS-7)|DSSV ''Pressure Drop'']] combined with manned descents revealed that they undulate with slopes and piles of rocks above a bed of [[pelagic sediment#Oozes|pelagic ooze]]. This conforms with the description of Challenger Deep as consisting of an elongated seabed section with distinct sub-basins or sediment-filled pools.<ref name="20211021ORP"/>

==Surveys and bathymetry==
{{duplication|section=yes|dupe=#Descents|othersections=y|date=August 2020}}

Over many years, the search for, and investigation of, the location of the maximum depth of the world's oceans has involved many different vessels, and continues into the twenty-first century.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep">{{cite journal |last=Nakanishi|first=Masao |title=A precise bathymetric map of the world's deepest seafloor, Challenger Deep in the Mariana Trench |journal=Marine Geophysical Research |volume=32 |issue=4 |pages=455–63 |url=http://naosite.lb.nagasaki-u.ac.jp/dspace/bitstream/10069/25460/1/MGR_Hashimoto.pdf |archive-url=https://web.archive.org/web/20150903220055/http://naosite.lb.nagasaki-u.ac.jp/dspace/bitstream/10069/25460/1/MGR_Hashimoto.pdf |archive-date=2015-09-03 |url-status=live |date=10 April 2011 |access-date=30 March 2012 |bibcode=2011MarGR..32..455N |doi=10.1007/s11001-011-9134-0 |hdl=10069/25460 |citeseerx=10.1.1.453.5784 |s2cid=55042876}}</ref>

The accuracy of determining geographical location, and the beamwidth of (multibeam) echosounder systems, limits the horizontal and vertical bathymetric [[sensor resolution]] that hydrographers can obtain from onsite data. This is especially important when sounding in deep water, as the resulting footprint of an acoustic pulse gets large once it reaches a distant sea floor. Further, sonar operation is affected by variations in [[Speed of sound#Seawater|sound speed]], particularly in the vertical plane. The speed is determined by the water's [[bulk modulus]], [[mass]], and [[density]]. The bulk modulus is affected by temperature, [[pressure]], and dissolved impurities (usually [[salinity]]).

===1875 – HMS ''Challenger''===
In 1875, during her transit from the [[Admiralty Islands]] in the [[Bismarck Archipelago]] to [[Yokohama]] in Japan, the three-masted sailing corvette HMS ''[[HMS Challenger (1858)|''Challenger'']] ''attempted to make landfall at [[Spanish East Indies|Spanish Marianas]] (now [[Guam]]), but was set to the west by "baffling winds" preventing her crew from "visiting either the [[Caroline Islands|Carolines]] or the [[Mariana Islands|Ladrones]]."<ref>Spry, W.J.J., "The Cruise of the Challenger", 1877, page 273</ref> Their altered path took them over the undersea canyon which later became known as the Challenger Deep. [[Sounding line|Depth soundings]] were taken by Baillie-weighted marked rope, and geographical locations were determined by [[celestial navigation]] (to an estimated accuracy of two nautical miles). One of their samples was taken within fifteen miles of the deepest spot in all of Earth's oceans. On 23 March 1875, at sample station number #225, HMS ''Challenger'' recorded the bottom at {{convert|4475|fathom|lk=on}} deep, (the deepest sounding of her three-plus-year eastward [[circumnavigation]] of the Earth) at {{Coord|11|24|N|143|16|E}} – and confirmed it with a second sounding at the same location.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/> The serendipitous discovery of Earth's deepest depression by [[Challenger expedition|history's first major scientific expedition devoted entirely to the emerging science of oceanography]], was incredibly good fortune, and especially notable when compared to the Earth's third deepest site (the [[Sirena Deep]] only 150 nautical miles east of the Challenger Deep), which would remain undiscovered for another 122 years.

===1951 – SV HMS ''Challenger II''===
[[File:Gaskell HMS Challenger II.jpg|thumb|Chief Scientist [[Tom Gaskell]], left, aboard [[HMS Challenger (1931)|HMS ''Challenger II'']], 1951]]

Seventy-five years later, the 1,140-ton British survey vessel [[HMS Challenger (1931)|HMS ''Challenger II'']], on her three-year westward [[circumnavigation]] of Earth, investigated the extreme depths southwest of Guam reported in 1875 by her predecessor, HMS ''Challenger''. On her southbound track from [[Occupation of Japan|Japan]] to [[New Zealand]] (May–July 1951), ''Challenger II'' conducted a survey of the [[Mariana Trench|Marianas Trench]] between Guam and [[Ulithi]] atoll, using seismic-sized bomb-soundings and recorded a maximum depth of {{convert|5663|fathom|0}}.{{citation needed|date=March 2021}} The depth was beyond ''Challenger II''{{'s}} [[echo sounder]] capability to verify, so they resorted to using a taut wire with "140&nbsp;lbs of scrap iron", and documented a depth of {{convert|5899|fathom|0}}.<ref name="Ritchie, G.S. 1958 p.225">Ritchie, G. S., ''Challenger, the Life of a Survey Ship'', Abelard-Shuman (1958), page 225</ref> The Senior Scientist aboard ''Challenger II'', [[Thomas Gaskell]],<ref>{{Cite web |title=Marine Gazetteer Placedetails - Gaskell Ridge |url=https://www.marineregions.org/gazetteer.php?p=details&id=7319 |url-status=live |website=Marineregions.org |access-date=23 January 2023 |archive-date=23 January 2023 |archive-url=https://web.archive.org/web/20230123230233/https://www.marineregions.org/gazetteer.php?p=details&id=7319}}</ref> recalled: <blockquote>[I]t took from ten past five in the evening until twenty to seven, that is an hour and a half, for the iron weight to fall to the sea-bottom. It was almost dark by the time the weight struck, but great excitement greeted the reading...<ref>{{Cite book |last=Gaskell |first=Thomas F. |title=Under The Deep Oceans: Twentieth Century Voyages of Discovery |publisher=Eyre & Spottiswood |year=1960 |edition=1st |page=121}}</ref></blockquote>In New Zealand, the ''Challenger II'' team gained the assistance of the Royal New Zealand Dockyard, "who managed to boost the echo sounder to record at the greatest depths".<ref name="Ritchie, G.S. 1958 p.225"/> They returned to the "Marianas Deep" (sic)<ref>Gaskell, T. F., "HMS Challenger's World Voyage 1950–52", Part I. Atlantic & Pacific Oceans, International Hydrographic Review, Volume XXX, number 2 (2018), page 119</ref> in October 1951. Using their newly improved echo sounder, they ran survey lines at right angles to the axis of the trench and discovered "a considerable area of a depth greater than {{convert|5900|fathom|0}}" – later identified as the Challenger Deep's ''western'' basin. The greatest depth recorded was {{convert|5940|fathom|0}},<ref>Ritchie, G. S., ''Challenger, the Life of a Survey Ship'', Abelard-Shuman (1958), page 229</ref> at {{Coord|11|19|N|142|15|E}}.<ref>{{cite journal |last=Fujioka |first=K |display-authors=et al |title=Morphology and origin of the Challenger Deep in the Southern Mariana Trench |journal=Geophysical Research Letters |volume=29 |issue=10 |date=18 May 2002 |pages=10–1–4|doi=10.1029/2001GL013595|bibcode=2002GeoRL..29.1372F |s2cid=129148518}}</ref> Navigational accuracy of several hundred meters was attained by celestial navigation and [[LORAN|LORAN-A]]. As Gaskell explained, the measurement <blockquote>was not more than 50 miles from the spot where the nineteenth-century ''Challenger'' found her deepest depth [...] and it may be thought fitting that a ship with the name ''Challenger'' should put the seal on the work of that great pioneering expedition of oceanography.<ref name=":1" /></blockquote>The term "Challenger Deep" came into use after this 1951–52 ''Challenger'' circumnavigation, and commemorates both British ships of that name involved with the discovery of the deepest basin of the world's oceans.[[File:Kaliningrad 05-2017 img62 Ocean Museum.jpg|thumb|Research vessel ''Vityaz'' in [[Kaliningrad]] "Museum of world ocean"]]

===1957–1958 – RV ''Vityaz''===
In August 1957, the [[Soviet Union|Soviet]] 3,248-ton Vernadsky Institute of Geochemistry research vessel {{ship|RV|Vityaz|1939|2}} recorded a maximum depth of {{convert|11034|±|50|m|ft|0|abbr=on}} at {{Coord|11|20.9|N|142|11.5|E}} in the western basin of the Challenger Deep during a brief transit of the area on Cruise #25. She returned in 1958, Cruise #27, to conduct a detailed single beam bathymetry survey involving over a dozen transects of the Deep, with an extensive examination of the western basin and a quick peek into the eastern basin.<ref>{{cite web |url=https://maps.ngdc.noaa.gov/viewers/bathymetry/ |title=Bathymetric Data Viewer |publisher=[[NOAA]] |access-date=9 November 2019 |archive-date=9 July 2017 |archive-url=https://web.archive.org/web/20170709195021/https://maps.ngdc.noaa.gov/viewers/bathymetry/}} [Single-Beam Surveys; Survey ID–VIT27, then zoom into Challenger Deep]</ref><ref>Hanson, P. P., "Maximum Depths of the Pacific Ocean", ''Priroda'' number 6 (in Russian), 1959, pages 84–88.</ref> Fisher records a total of three ''Vityaz'' sounding locations on Figure 2 "Trenches" (1963), one within yards of the 142°11.5' E location, and a third at {{Coord|11|20.0|N|142|07|E}}, all with {{convert|11034|±|50|m|ft|0|abbr=on}} depth.<ref>Fisher, R. L., and H. H. Hess, ''Trenches, in The Sea'', volume 3, Figure 2, page 417, 1963</ref> The depths were considered [[Outlier|statistical outliers]], and a depth greater than 11,000 m has never been proven. Taira reports that if ''Vityaz''{{'s}} depth was corrected with the same methodology used by the Japanese RV ''Hakuho Maru'' expedition of December 1992, it would be presented as {{convert|10983|±|50|m|ft|0|abbr=on}},<ref>Taira, K., "Deep CTD Casts in the Challenger Deep, Mariana Trench", ''Journal of Oceanography'', Volume 61, page 453, 2005</ref> as opposed to modern depths from multibeam echosounder systems greater than {{convert|10900|m|ft}} with the NOAA accepted maximum of {{convert|10995|±|10|m|ft|0|abbr=on}} in the western basin.<ref>Nakanishi, M., "A precise bathymetric map of the world's deepest seafloor, Challenger Deep in the Mariana Trench", ''Marine Geophysical Research'', Table 3, page 13, 10 April 2011</ref><ref>{{cite web |url=https://maps.ngdc.noaa.gov/viewers/bathymetry/ |title=Bathymetric Data Viewer |publisher=NOAA |access-date=9 November 2019 |archive-date=9 July 2017 |archive-url=https://web.archive.org/web/20170709195021/https://maps.ngdc.noaa.gov/viewers/bathymetry/}} [zoom into Challenger Deep to 1&nbsp;km]</ref>

===1959 – RV ''Stranger''===
The first definitive verification of both the depth and location of the Challenger Deep (western basin) was determined by Dr. R. L. Fisher from the [[Scripps Institution of Oceanography]], aboard the 325-ton research vessel ''Stranger''. Using explosive soundings, they recorded {{convert|10850|±|20|m|ft|0|abbr=on}} at/near {{Coord|11|18|N|142|14|E}} in July 1959. ''Stranger'' used celestial and [[LORAN-C]] for navigation.<ref>{{cite web |date= |title=Challenger Deep |url=https://www.ngdc.noaa.gov/gazetteer/ |publisher=NOAA |access-date=6 November 2019 |archive-date=23 April 2021 |archive-url=https://web.archive.org/web/20210423032853/https://www.ngdc.noaa.gov/gazetteer/ |url-status=live}}</ref><ref>Fisher, R. L., and H. H. Hess, "Trenches", in ''The Earth Beneath the Sea'', volume 3, pages 411–436, Table 1, 1963</ref> LORAN-C navigation provided geographical accuracy of {{convert|460|m|ft|0|abbr=on}} or better.<ref>Floyd, P. A., ''Ocean Basalts'', Springer, 1991, page 12</ref> According to another source RV ''Stranger'' using bomb-sounding surveyed a maximum depth of {{convert|10915|±|10|m|ft|0|abbr=on}} at {{Coord|11|20.0|N|142|11.8|E}}.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/> Discrepancies between the geographical location (lat/long) of ''Stranger''{{'s}} deepest depths and those from earlier expeditions (''Challenger II'' 1951; ''Vityaz'' 1957 and 1958) "are probably due to uncertainties in fixing the ships' positions".<ref name="Fisher, Trenches p. 416">Fisher, "Trenches", ''The Earth Beneath the Sea'', page 416, 1963</ref> ''Stranger''{{'s}} north-south zig-zag survey passed well to the east of the eastern basin southbound, and well to the west of the eastern basin northbound, thus failed to discover the eastern basin of the Challenger Deep.<ref>Fisher, "Trenches", ''The Earth Beneath the Sea'', page 417, Figure 2, 1963</ref> The maximum depth measured near longitude 142°30'E was {{convert|10760|±|20|m|ft|0|abbr=on}}, about 10&nbsp;km west of the eastern basin's deepest point. This was an important gap in information, as the eastern basin was later reported as deeper than the other two basins.
''Stranger'' crossed the center basin twice, measuring a maximum depth of {{convert|10830|±|20|m|ft|0|abbr=on}} in the vicinity of 142°22'E. At the western end of the central basin (approximately 142°18'E), they recorded a depth of {{convert|10805|±|20|m|ft|0|abbr=on}}.<ref name="jproc.ca">{{cite web |url=http://www.jproc.ca/hyperbolic/loran_c.html |title=Loran-C Introduction |website=Hyperbolic Radionavigation Systems |access-date=6 November 2019 |archive-date=10 June 2021 |archive-url=https://web.archive.org/web/20210610004404/http://jproc.ca/hyperbolic/loran_c.html |url-status=live}}</ref>{{failed verification|date=January 2020}}
The western basin received four [[transects]] by ''Stranger'', recording depths of {{convert|10830|±|20|m|ft|0|abbr=on}} toward the central basin, near where ''Trieste'' dived in 1960 (vicinity {{Coord|11|18.5|N|142|15.5|E}}, and where ''Challenger II'', in 1950, recorded {{convert|10863|±|35|m|ft|0|abbr=on}}. At the far western end of the ''western'' basin (about 142°11'E), the ''Stranger'' recorded {{convert|10850|±|20|m|ft|0|abbr=on}}, some 6&nbsp;km south of the location where ''Vityaz'' recorded {{convert|11034|±|50|m|ft|0|abbr=on}} in 1957–1958. Fisher stated: "differences in the ''Vitiaz'' [sic] and ''Stranger''–''Challenger II'' depths can be attributed to the [sound] velocity correction function used".<ref name="Fisher, Trenches p. 416"/> 
After investigating the Challenger Deep, ''Stranger'' proceeded to the [[Philippine Trench]] and transected the trench over twenty times in August 1959, finding a maximum depth of {{convert|10030|±|10|m|ft|0|abbr=on}}, and thus established that the Challenger Deep was about {{convert|800|m|ft}} deeper than the Philippine Trench.<ref>Fisher, "Trenches", ''The Earth Beneath the Sea'', Table I, page 418</ref> The 1959 ''Stranger'' surveys of the Challenger Deep and of the Philippine Trench informed the U.S. Navy as to the appropriate site for ''Trieste''{{'s}} record dive in 1960.<ref>{{cite magazine |last1=Fisher |first1=Robert L. |year=2009 |title=Meanwhile, Back on the Surface |url=https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf |magazine=Marine Technology Society Journal |language=en |publisher=[[Marine Technology Society]] |volume=43 |issue=5 |pages=16–19 |issn=0025-3324 |archive-url=https://web.archive.org/web/20230416014230/https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf |archive-date=2023-04-16 |access-date=2024-01-12}}</ref>

===1962 – RV ''Spencer F. Baird''===
The ''Proa Expedition, Leg 2'', returned Fisher to the Challenger Deep on 12–13 April 1962 aboard the [[Scripps Institution of Oceanography|Scripps]] research vessel ''Spencer F. Baird'' (formerly the steel-hulled US Army large tug ''LT-581'') and employed a Precision Depth Recorder (PDR) to verify the extreme depths previously reported. They recorded a maximum depth of {{convert|10915|m|}} (location not available).<ref>Fisher, Trenches, The Earth Beneath the Sea, Table I, page 418 Table 1</ref> Additionally, at location "H-4" in the Challenger Deep, the expedition cast three taut-wire soundings: on 12 April, the first cast was to 5,078 fathoms (corrected for wire angle) {{convert|9287|m|ft}} at {{Coord|11|23|N|142|19.5|E}} in the central basin (Up until 1965, US research vessels recorded soundings in fathoms). The second cast, also on 12 April, was to 5,000<sup>+</sup> fathoms at {{Coord|11|20.5|N|142|22.5|E}} in the central basin. On 13 April, the final cast recorded 5,297 fathoms (corrected for wire angle) {{convert|9687|m|ft}} at {{Coord|11|17.5|N|142|11|E}} (the western basin).<ref>"Physical And Chemical Data, PROA Expedition 12 April – 6 July 1962", SIO 66-16, page 3</ref> They were chased off by a hurricane after only two days on-site. Once again, Fisher entirely missed the eastern basin of the Challenger Deep, which later proved to contain the deepest depths.

===1975–1980 – RV ''Thomas Washington''===
The Scripps Institution of Oceanography deployed the 1,490-ton Navy-owned, civilian-crewed research vessel ''[[USNS Thomas Washington (T-AGOR-10)|Thomas Washington]]'' (AGOR-10) to the Mariana Trench on several expeditions from 1975 to 1986. The first of these was the ''Eurydice Expedition, Leg 8'' which brought Fisher back to the Challenger Deep's western basin from 28–31 March 1975.<ref>"Eurydice Expedition, Leg 8, R/V ''Thomas Washington'', Informal Report 24–31 March 1975", [[Scripps Institution of Oceanography|SIO]] Geological Data Center, 27 June 1975.</ref> ''Thomas Washington'' established geodetic positioning by ([[Satellite navigation|SATNAV]]) with Autolog Gyro and EM Log. [[Bathymetry|Bathymetrics]] were by a 12&nbsp;kHz Precision Depth Recorder (PDR) with a single 60° beam. They mapped one, "possibly two", axial basins with a depth of {{convert|10915|±|20|m|ft|0|abbr=on}}.<ref>"Eurydice Expedition, Leg 8, R/V ''Thomas Washington'', Informal Report 24–31 March 1975", [[Scripps Institution of Oceanography|SIO]] Geological Data Center, 27 June 1975, Track Plot, page 4</ref><ref>{{cite web |url=http://maps.continentalshelf.org/geodas/ERDC08WT.htm |publisher=Continental Shelf Programme |title=Survey Identifier: ERDC08WT |access-date=11 November 2019 |archive-date=15 May 2021 |archive-url=https://web.archive.org/web/20210515055908/http://maps.continentalshelf.org/geodas/ERDC08WT.htm |url-status=live}}</ref> Five dredges were hauled 27–31 March, all into or slightly north of the deepest depths of the western basin. Fisher noted that this survey of the Challenger Deep (western basin) had "provided nothing to support and much to refute recent claims of depths there greater than {{convert|10915|±|20|m|ft|0|abbr=on}}."<ref>Fisher, R., [http://siox.sdsc.edu/secureGetObj.php?filename=SIOGDC_ERDC08WT_20070608200108001_20070608200108001_ERDC08WT_weekly_reports.txt&col=ERDC08WT "Eurydice Expedition Leg 08, Weekly Reports"] {{Webarchive|url=https://web.archive.org/web/20211224220500/http://siox.sdsc.edu/secureGetObj.php?filename=SIOGDC_ERDC08WT_20070608200108001_20070608200108001_ERDC08WT_weekly_reports.txt&col=ERDC08WT |date=24 December 2021}}, Scripps Institution of Oceanography, 1975.</ref> While Fisher missed the eastern basin of the Challenger Deep (for the third time), he did report a deep depression about 150 nautical miles east of the western basin. The 25 March dredge haul at {{Coord|12|03.72|N|142|33.42|E}} encountered {{convert|10015|m|ft}}, which pre-shadowed by 22 years the discovery of HMRG Deep/[[Sirena Deep]] in 1997.<ref>{{cite AV media |title=ERDC08WT-024D |url=https://library.ucsd.edu/dc/object/bb4745506c |author=Thomas Washington |type=Dredge |location=Scripps Institution of Oceanography, Geological Collections |date=1975 |id=IGSN: SIO001559 |access-date=11 April 2022 |archive-date=17 October 2015 |archive-url=https://web.archive.org/web/20151017090236/http://library.ucsd.edu/dc/object/bb4745506c |url-status=live}}</ref> The deepest waters of the HMRG Deep/Sirena Deep at {{convert|10714|±|20|m|ft|0|abbr=on}} are centered at/near {{Coord|12|03.94|N|142|34.866|E}}, approximately 2.65&nbsp;km from Fisher's 25 March 1975 {{convert|10015|m|ft}} dredge haul.

On Scripps Institution of Oceanography's ''INDOPAC Expedition Leg 3'',<ref>{{cite web |url=http://maps.continentalshelf.org/geodas/INDP03WT.htm |publisher=Continental Shelf Programme |title=Survey Identifier: INDP03WT |access-date=21 January 2020 |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928043559/http://maps.continentalshelf.org/geodas/INDP03WT.htm |url-status=live}}</ref> the chief scientist, Dr. Joseph L. Reid, and oceanographer Arnold W. Mantyla made a hydrocast of a free vehicle<ref>INDOPAC Expedition, Leg 3, R/V. Thomas Washington Informal Report, SIO INDP03WT)</ref> (a special-purpose [[benthic lander]] (or "baited camera") for measurements of water temperature and salinity) on 27 May 1976 into the western basin of the Challenger Deep, "Station 21", at {{Coord|11|19.9|N|142|10.8|E}} at about {{convert|10840|m|ft}} depth.<ref>Indopac Expedition Leg 3 Weekly Summary J. Reid</ref><ref>Taira, K, "Deep CTD Casts in the Challenger Deep", ''Journal of Oceanography'', Volume 61, 2005, page 450</ref> On ''INDOPAC Expedition Leg 9'', under chief scientist A. Aristides Yayanos, ''Thomas Washington'' spent nine days from 13–21 January 1977 conducting an extensive and detailed investigation of the Challenger Deep, mainly with biological objectives.<ref>INDOPAC Expedition, Leg 9, R/V. Thomas Washington Informal Report, SIO INDP09WT</ref> "Echo soundings were carried out primarily with a 3.5 kHz single-beam system, with a 12 kHz echosounder operated in addition some of the time" (the 12&nbsp;kHz system was activated for testing on 16 January).<ref>Cruise Report, INDOPAC Expedition, Leg 9</ref> A benthic lander was put into the western basin ({{Coord|11|19.7|N|142|09.3|E}}) on 13 January, bottoming at {{convert|10663|m|ft}} and recovered 50 hours later in damaged condition. Quickly repaired, it was again put down on the 15th to {{convert|10559|m|ft}} depth at {{Coord|11|23.3|N|142|13.8|E}}. It was recovered on the 17th with excellent photography of [[amphipods]] (shrimp) from the Challenger Deep's western basin. The benthic lander was put down for the third and last time on the 17th, at {{Coord|11|20.1|N|142|25.2|E}}, in the central basin at a depth of {{convert|10285|m|ft}}. The benthic lander was not recovered and may remain on the bottom in the vicinity of {{Coord|11|20.1|N|142|25.2|E}}. Free traps and pressure-retaining traps were put down at eight locations from 13 to 19 January into the western basin, at depths ranging from {{convert|7353|to(-)|10715|m|ft}}. Both the free traps and the pressure-retaining traps brought up good sample amphipods for study. While the ship briefly visited the area of the eastern basin, the expedition did not recognize it as potentially the deepest of the three Challenger Deep basins.<ref>{{cite web |url=https://gis.ngdc.noaa.gov/viewers/redirect.html?layers=multibeam&minx=144.00209&maxx=155.49962&miny=-41.348255&maxy=13.947198 |title=Bathymetric Data Viewer |date=14 December 2018 |publisher=NOAA |access-date=11 November 2019 |archive-date=24 September 2020 |archive-url=https://web.archive.org/web/20200924011537/https://maps.ngdc.noaa.gov/viewers/bathymetry/?layers=multibeam&minx=144.00209&maxx=155.49962&miny=-41.348255&maxy=13.947198 |url-status=live}}</ref>
	
''Thomas Washington'' returned briefly to the Challenger Deep on 17–19 October 1978 during ''Mariana Expedition Leg 5'' under chief scientist James W. Hawkins.<ref>{{Cite book |chapter-url=https://library.ucsd.edu/dc/object/bb4202429z |title=MARA05WT Mariana Leg 5 – Cruise Report |publisher=Geological Data Center at Scripps Institution of Oceanography |date=January 1979 |doi=10.6075/J01J981F |author1=Geological Data Center at Scripps Institution of Oceanography |chapter=Cruise Report |access-date=11 November 2019 |archive-date=11 November 2019 |archive-url=https://web.archive.org/web/20191111075423/https://library.ucsd.edu/dc/object/bb4202429z |url-status=live}}</ref> The ship tracked to the south and west of the eastern basin, and recorded depths between {{convert|5093|and(-)|7182|m|ft}}. Another miss. On ''Mariana Expedition Leg 8'', under chief scientist Yayanos, ''Thomas Washington'' was again involved, from 12–21 December 1978, with an intensive biological study of the western and central basins of the Challenger Deep.<ref>{{cite web |url=http://maps.continentalshelf.org/geodas/MARA08WT.htm |publisher=Continental Shelf Programme |title=Survey Identifier: MARA08WT |access-date=11 November 2019 |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928063930/http://maps.continentalshelf.org/geodas/MARA08WT.htm |url-status=live}}</ref> Fourteen traps and pressure-retaining traps were put down to depths ranging from {{convert|10455|to(-)|10927|m|ft}}; the greatest depth was at {{Coord|11|20.0|N|142|11.8|E}}. All of the 10,900-plus m recordings were in the western basin. The {{convert|10455|m|ft}} depth was furthest east at 142°26.4' E (in the central basin), about 17&nbsp;km west of the eastern basin. Again, focused efforts on the known areas of extreme depths (the western and central basins) were so tight that the eastern basin again was missed by this expedition.<ref>Yayanos, A. A. et.al, "Dependence of Reproduction Rate on Pressure as a Hallmark of Deep-Sea Bacteria", ''Applied and Environmental Microbiology'', December 1982, pages 1356–1361</ref>

From 20 to 30 November 1980, ''Thomas Washington'' was on site at the western basin of the Challenger Deep, as part of ''Rama Expedition Leg 7'', again with chief-scientist Dr. A. A. Yayanos.<ref>{{cite web |url=http://maps.continentalshelf.org/geodas/RAMA07WT.htm |publisher=Continental Shelf Programme |title=Survey Identifier: RAMA07WT |access-date=11 November 2019 |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928050205/http://maps.continentalshelf.org/geodas/RAMA07WT.htm |url-status=live}}</ref> Yayanos directed ''Thomas Washington'' in arguably the most extensive and wide-ranging of all single-beam bathymetric examinations of the Challenger Deep ever undertaken, with dozens of transits of the western basin, and ranging far into the [[backarc]] of the Challenger Deep (northward), with significant excursions into the Pacific Plate (southward) and along the trench axis to the east.<ref>{{cite web |url=https://maps.ngdc.noaa.gov/viewers/bathymetry/ |title=Bathymetric Data Viewer |publisher=NOAA |access-date=9 November 2019 |archive-date=9 July 2017 |archive-url=https://web.archive.org/web/20170709195021/https://maps.ngdc.noaa.gov/viewers/bathymetry/}} [select single beam and enter RAMA07WT]</ref> They hauled eight dredges in the western basin to depths ranging from {{convert|10015|to(-)|10900|m|ft}}, and between hauls, cast thirteen free vertical traps. The dredging and traps were for biological investigation of the bottom. In the first successful retrieval of a live animal from the Challenger Deep, on 21 November 1980 in the western basin at {{Coord|11|18.7|N|142|11.6|E}}, Yayanos recovered a live amphipod from about 10,900 meters depth with a pressurized trap.<ref>Yayanos, A. A., [https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_2.pdf "Recovery of Live Amphipods at over 102MPa from the Mariana Trench"] {{Webarchive|url=https://web.archive.org/web/20200922225246/https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_2.pdf |date=22 September 2020}}, ''Marine Technology Society Journal'', Winter 2009, Volume 43, Number 5, page 134.</ref> Once again, other than a brief look into the eastern basin, all bathymetric and biological investigations were into the western basin.<ref>Yayanos, F., Informal Report and Index of Navigation, Depth and Magnetic Data – Rama Expedition, Leg 7, 31 October 1980 – 1 December 1980, R/V Thomas Washington (GDC Cruise I.D. #181)</ref>

===1976–1977 – RV ''Kana Keoki''===
[[File:Cross section of mariana trench.svg|thumb|upright=1.75|Pacific plate subduction at the Challenger Deep]]
On Leg 3 of the Hawaii Institute of Geophysics' (HIG) expedition 76010303, the {{convert|156|ft|0|adj=on}} research vessel ''Kana Keoki'' departed Guam primarily for a [[seismic]] investigation of the Challenger Deep area, under chief scientist Donald M. Hussong.<ref>{{cite book |chapter-url=ftp://soest.hawaii.edu/dkarl/misc/dave/UH%26theSea/Q-Chapter13.pdf |title=UH and the Sea |first=David |last=Karl |chapter=UH Fleet Assets (1962–2003) |pages=15–21 |access-date=24 November 2019 |archive-date=18 March 2023 |archive-url=https://web.archive.org/web/20230318144755/ftp://soest.hawaii.edu/dkarl/misc/dave/UH%26theSea/Q-Chapter13.pdf |url-status=live}}</ref> The ship was equipped with [[Seismic source|air guns]] (for seismic reflection soundings deep into the [[Earth's mantle]]), [[magnetometer]], [[gravimeter]], 3.5&nbsp;kHz and 12&nbsp;kHz sonar transducers, and precision depth recorders. They ran the Deep from east to west, collecting single beam bathymetry, magnetic and gravity measurements, and employed the air guns along the trench axis, and well into the [[backarc]] and [[forearc]], from 13 to 15 March 1976. Thence they proceeded south to the [[Ontong Java Plateau]]. All three deep basins of the Challenger Deep were covered, but ''Kana Keoki'' recorded a maximum depth of {{convert|7800|m|ft|0|abbr=on}}.<ref>MGD77-398858 {{full citation needed|date=January 2020}}</ref> Seismic information developed from this survey was instrumental in gaining an understanding of the [[subduction]] of the [[Pacific Plate]] under the [[Philippine Sea Plate]].<ref>"International Decade of Ocean Exploration, Progress Report Volume 7, April 1977 to April 1978", US Dept of Commerce, NOAA, Environmental Data and Information Service, October 1978, page 61</ref> In 1977, ''Kana Keoki'' returned to the Challenger Deep area for wider coverage of the forearc and backarc.

===1984 – SV ''Takuyo''===
The Hydrographic Department, Maritime Safety Agency, Japan (JHOD) deployed the newly commissioned 2,600-ton survey vessel ''Takuyo'' (HL 02) to the Challenger Deep 17–19 February 1984.<ref>Nakanishi, A., New Japanese Survey Vessel "Takuyo", International Hydrographic Review, Monaco, LXII (s), July 1985, pages 51–57.</ref> ''Takuyo'' was the first Japanese ship to be equipped with the new narrowbeam [[SeaBeam]] [[Multibeam echosounder|multi-beam sonar echosounder]], and was the first [[survey ship]] with multi-beam capability to survey the Challenger Deep. The system was so new that JHOD had to develop their own software for drawing bathymetric charts based on the SeaBeam digital data.<ref>Asada, A., "Contour Processing of 3-D Image Processing of Sea Beam Bathymetric Data", ''International Hydrographic Review'', Monaco, LXV(1), January 1988; pages 65–80.</ref> In just three days, they tracked 500 miles of sounding lines, and covered about 140&nbsp;km{{sup|2}} of the Challenger Deep with multibeam ensonification. Under chief scientist Hideo Nishida, they used [[CTD (instrument)|CTD]] temperature and salinity data from the top {{convert|4500|m|ft|0}} of the [[water column]] to correct depth measurements, and later conferred with Scripps Institution of Oceanography (including Fisher), and other [[GEBCO]] experts to confirm their depth correction methodology. They employed a combination of [[NAVSAT]], [[LORAN-C]] and [[Omega (navigation system)|OMEGA]] systems for geodetic positioning with accuracy better than {{convert|400|m|ft}}. The deepest location recorded was {{convert|10920|±|10|m|ft|0|abbr=on}} at {{Coord|11|22.4|N|142|35.5|E}}; for the first time documenting the eastern basin as the deepest of the three [[en echelon]] pools.<ref>Yashima, K., [https://www.gebco.net/about_us/gebco_symposium/documents/poster_worlds_greatest_depth.pdf "World's Greatest Depth in Challenger Deep (Mariana Trench)"] {{Webarchive|url=https://web.archive.org/web/20200727192440/https://www.gebco.net/about_us/gebco_symposium/documents/poster_worlds_greatest_depth.pdf |date=27 July 2020}}, 1994.</ref> In 1993, [[GEBCO]] recognized the {{convert|10920|±|10|m|ft|0|abbr=on}} report as the deepest depth of the world's oceans.<ref>GEBCO 5.06, 1993 Guiding Committee Minutes</ref> Technological advances such as improved [[multi-beam sonar]] would be the driving force in uncovering the mysteries of the Challenger Deep into the future.

===1986 – RV ''Thomas Washington''===
The Scripps research vessel ''Thomas Washington''{{'s}} returned to the Challenger Deep in 1986 during the ''Papatua Expedition, Leg 8'', mounting one of the first commercial multi-beam echosounders capable of reaching into the deepest trenches, i.e. the 16-beam Seabeam "Classic". This allowed chief scientist Yayanos an opportunity to transit the Challenger Deep with the most modern depth-sounding equipment available. During the pre-midnight hours of 21 April 1986, the multibeam echosounder produced a map of the Challenger Deep bottom with a [[Swathe|swath]] of about 5–7 miles wide. The maximum depth recorded was {{convert|10804|m|ft}} (location of depth is not available). Yayanos noted: "The lasting impression from this cruise comes from the thoughts of the revolutionary things that Seabeam data can do for deep biology."<ref>Yayanos, A. A., R/V Thomas Washington KGWU, Weekly Report, Papatua Expedition Leg 8, 212218Z April 1986</ref>

===1988 – RV ''Moana Wave''===
On 22 August 1988, the U.S. Navy-owned 1,000-ton research vessel ''Moana Wave'' (AGOR-22), operated by the Hawaii Institute of Geophysics (HIG), [[University of Hawaiʻi]], under the direction of chief scientist [[Robert Thunell|Robert C. Thunell]] from the [[University of South Carolina]], transited northwesterly across the central basin of the Challenger Deep, conducting a single-beam bathymetry track by their 3.5&nbsp;kHz narrow (30-degs) beam echosounder with a Precision Depth Recorder. In addition to sonar bathymetry, they took 44 [[gravity core]]s and 21 [[box core]]s of bottom sediments. The deepest echosoundings recorded were {{convert|10,656|to(-)|10,916|m|ft}}, with the greatest depth at 11°22′N 142°25′E in the central basin.<ref>Physical and Chemical Data, RISEPAC Expedition 7–23 December 1961; Proa Expedition 12 April – 6 July 1962; and Zephyrus Expedition 12 July – 26 September 1962; SIO Reference 66-16</ref> This was the first indication that all three basins contained depths in excess of {{convert|10,900|m|ft}}.

[[File:Hakuho Maru, Fremantle, 2019 (06).jpg|thumb|The RV ''Hakuhō Maru'']]

===1992 – RV ''Hakuhō Maru''===
The 3,987-ton Japanese research vessel ''Hakuhō Maru'', an Ocean Research Institute – University of Tokyo sponsored ship, on cruise KH-92-5 cast three Sea-Bird SBE-9 ultra-deep [[CTD (instrument)|CTD]] (conductivity-temperature-depth) profilers in a transverse line across the Challenger Deep on 1 December 1992. The center CTD was located at {{Coord|11|22.78|N|142|34.95|E}}, in the eastern basin, at {{convert|10989|m|ft}} by the SeaBeam depth recorder and {{convert|10884|m|ft}} by the CTD. The other two CTDs were cast 19.9&nbsp;km to the north and 16.1&nbsp;km to the south. ''Hakuhō Maru'' was equipped with a narrow beam SeaBeam 500 multi-beam echosounder for depth determination, and had an Auto-Nav system with inputs from [[Satellite Transit System|NAVSAT/NNSS]], GPS, Doppler Log, EM log and track display, with a [[Geodetic datum|geodetic positioning]] accuracy approaching {{convert|100|m|ft}}.<ref>{{cite web |url=https://www.aori.u-tokyo.ac.jp/english/coop/hakuhomaru.html |title=Research Vessel Hakuho Maru |publisher=Atmosphere and Ocean Research Institute, The University of Tokyo |access-date=21 January 2020 |archive-date=27 July 2020 |archive-url=https://web.archive.org/web/20200727192321/https://www.aori.u-tokyo.ac.jp/english/coop/hakuhomaru.html |url-status=live}}</ref> When conducting CTD operations in the Challenger deep, they used the SeaBeam as a single beam depth recorder. At {{Coord|11|22.6|N|142|35.0|E}} the corrected depth was {{convert|10989|m|ft}}, and at {{Coord|11|22.0|N|142|34.0|E}} the depth was {{convert|10927|m|ft}}; both in the ''eastern'' basin. This may demonstrate that the basins might not be flat [[Sedimentary basin|sedimentary pools]] but rather undulate with a difference of {{convert|50|m|ft}} or more. Taira revealed, "We considered that a [[Trough (geology)|trough]] deeper that ''Vitiaz''{{'s}} record by {{convert|5|m|ft}} was detected. There is a possibility that a depth exceeding {{convert|11000|m|ft|0}} with a horizontal scale less than the [[beam width]] of measurements exists in the Challenger Deep.<ref>Keisuke Taira, Daigo Yanagimoto and Shoji Kitagawa, [https://www.terrapub.co.jp/journals/JO/pdf/6103/61030447.pdf "Deep CTD Casts in the Challenger Deep, Mariana Trench"] {{Webarchive|url=https://web.archive.org/web/20200919101822/https://www.terrapub.co.jp/journals/JO/pdf/6103/61030447.pdf |date=19 September 2020}}, 447 ''Journal of Oceanography'', Volmne 61, pages 447–454, 2005</ref> Since each SeaBeam 2.7-degree beam width sonar ping expands to cover a circular area about {{convert|500|m|ft|0}} in diameter at {{convert|11000|m|ft|0}} depth, dips in the bottom that are less than that size would be difficult to detect from a sonar-emitting platform seven miles above.

[[File:JAMSTEC Yokosuka P5123676.jpg|thumb|RV ''Yokosuka'' was used as the support ship for ROV ''Kaikō''.]]

===1996 – RV ''Yokosuka''===
For most of 1995 and into 1996, the [[Japan Agency for Marine-Earth Science and Technology]] (JAMSTEC) employed the 4,439-ton Research Vessel ''Yokosuka'' to conduct the testing and workup of the 11,000-meter remotely-operated vehicle (ROV) ''[[Kaikō ROV|Kaikō]]'', and the 6,500 meter ROV ''Shinkai.'' It was not until February 1996, during ''Yokosuka''{{'s}} cruise Y96-06, that ''Kaikō'' was ready for its first full depth dives. On this cruise, JAMSTEC established an area of the Challenger Deep (11°10'N to 11°30'N, by 141°50'E to 143°00'E{{snd}}which later was recognized as containing three separate pools/basins en echelon, each with depths in excess of {{convert|10900|m|0|abbr=on}}) toward which JAMSTEC expeditions would concentrate their investigations for the next two decades.<ref>Kairei Cruise Report KR-08-05, page 8</ref><ref>Kairei Cruise Report KR-14-01, page 5</ref> The Yokosuka employed a 151-beam SeaBeam 2112 12&nbsp;kHz multibeam echosounder, allowing search swaths 12–15&nbsp;km in width at {{convert|11000|m|ft|0}} depth. The depth accuracy of ''Yokosuka''{{'s}} Seabeam was about 0.1% of water depth (i.e. ± {{convert|110|m|ft|0}} for {{convert|11000|m|ft|0}} depth). The ship's dual GPS systems attained geodetic positioning within double digit meter ({{convert|100|m|ft|0}} or better) accuracy.

===1998, 1999 and 2002 – RV ''Kairei''===
Cruise KR98-01 sent JAMSTEC's two-year-old 4,517-ton Deep Sea Research Vessel RV ''Kairei'' south for a quick but thorough depth survey of the Challenger Deep, 11–13 January 1998, under chief scientist Kantaro Fujioka. Tracking largely along the trench axis of 070–250° they made five 80-km bathymetric survey tracks, spaced about 15 km apart, overlapping their SeaBeam 2112-004 (which now allowed sub-bottom profiling penetrating as much as 75 m below the bottom) while gaining gravity and magnetic data covering the entire Challenger Deep: western, central, and eastern basins.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.328883171084,142.59120750425,11;| title = search parameters "Kairei", "KR98-01")| access-date = 23 November 2019| archive-date = 28 February 2021| archive-url = https://web.archive.org/web/20210228060012/http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.328883171084,142.59120750425,11;| url-status = live}}</ref><ref>Okino, K. et.al., [https://pubs.usgs.gov/ds/2006/171/data/cruise-reports/2001/html/4ins/95.htm Subbottom profiler] {{Webarchive|url=https://web.archive.org/web/20200930170237/https://pubs.usgs.gov/ds/2006/171/data/cruise-reports/2001/html/4ins/95.htm |date=30 September 2020}}</ref><ref>{{Cite journal | url=https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2001GL013595 | doi=10.1029/2001GL013595 | title=Morphology and origin of the Challenger Deep in the Southern Mariana Trench | year=2002 | last1=Fujioka | first1=Kantaro | last2=Okino | first2=Kyoko | last3=Kanamatsu | first3=Toshiya | last4=Ohara | first4=Yasuhiko | journal=Geophysical Research Letters | volume=29 | issue=10 | page=1372 | bibcode=2002GeoRL..29.1372F | s2cid=129148518 | access-date=15 December 2019 | archive-date=15 December 2019 | archive-url=https://web.archive.org/web/20191215145658/https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2001GL013595 | url-status=live | url-access=subscription}}</ref>

[[File:JAMSTEC Deep Sea Research Ship Kairei P7214312.jpg|thumb|The Deep Sea Research Vessel RV ''Kairei'' was also used as the support ship for the ROV ''Kaikō''.]]

''Kairei'' returned in May 1998, cruise KR98-05, with [[Kaikō ROV|ROV ''Kaikō'']], under the direction of chief scientist Jun Hashimoto with both geophysical and biological goals. Their bathymetric survey from 14–26 May was the most intensive and thorough depth and seismic survey of the Challenger Deep performed to date. Each evening, ''Kaikō'' deployed for about four hours of bottom time for biological-related sampling, plus about seven hours of vertical transit time. When ''Kaikō'' was onboard for servicing, ''Kairei'' conducted bathymetric surveys and observations. ''Kairei'' gridded a survey area about 130&nbsp;km N–S by 110&nbsp;km E–W.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.328883171084,142.59120750425,11| title = – search parameters: "Kairei", "KR98-05"| access-date = 23 November 2019| archive-date = 28 February 2021| archive-url = https://web.archive.org/web/20210228060012/http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.328883171084,142.59120750425,11| url-status = live}}</ref> ''Kaikō'' made six dives (#71–75) all to the same location, (11°20.8' N, 142°12.35' E), near the {{convert|10900|m|ft}} bottom contour line in the western basin.<ref>{{cite web |url=http://www.godac.jamstec.go.jp/darwin/dive/kaiko/71/e |title=KAIKO Dive 71 Dive Data |website=DARWIN |publisher=JAMSTEC |access-date=21 January 2020 |archive-date=27 July 2020 |archive-url=https://web.archive.org/web/20200727202508/http://www.godac.jamstec.go.jp/darwin/dive/kaiko/71/e |url-status=live}}</ref>

The regional bathymetric map made from the data obtained in 1998 shows that the greatest depths in the eastern, central, and western depressions are {{convert|10922|±|74|m|ft|0|abbr=on}}, {{convert|10898|±|62|m|ft|0|abbr=on}}, and {{convert|10908|±|36|m|ft|0|abbr=on}}, respectively, making the eastern depression the deepest of the three.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/>

In 1999, ''Kairei'' revisited the Challenger Deep during cruise KR99-06. The results of the 1998–1999 surveys include the first recognition that the Challenger Deep consists of three "right-stepping en echelon individual basins bounded by the {{convert|10500|m|ft}} depth contour line. The size of [each of] the deeps are almost identical, 14–20 km long, 4&nbsp;km wide". They concluded with the proposal "that these three individual elongated deeps constitute the 'Challenger Deep', and [we] identify them as the East, Central and West Deep. The deepest depth we obtained during the swath mapping is {{convert|10938|m|ft}} in the West Deep (11°20.34' N, 142°13.20 E)."<ref>Fujioka, K. et.al., "Morphology and origin of the Challenger Deep in the Southern Marian Trench", ''Geophysical Research Letters'', Volume 29, number 10, 1372, 2002, pages 10–12</ref> The depth was "obtained during swath mapping&nbsp;... confirmed in both N–S and E-W swaths." Speed of sound corrections were from XBT to {{convert|1800|m|ft}}, and CTD below {{convert|1800|m|ft}}.

The cross track survey of the 1999 ''Kairei'' cruise shows that the greatest depths in the eastern, central, and western depressions are {{convert|10920|±|10|m|ft|0|abbr=on}}, {{convert|10894|±|14|m|ft|0|abbr=on}}, and {{convert|10907|±|13|m|ft|0|abbr=on}}, respectively, which supports the results of the previous survey.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/>

In 2002 ''Kairei'' revisited the Challenger Deep 16–25 October 2002, as cruise KR02-13 (a cooperative Japan-US-South Korea research program) with chief scientist Jun Hashimoto in charge; again with Kazuyoshi Hirata managing the ROV ''Kaikō'' team. On this survey, the size of each of the three basins was refined to 6–10&nbsp;km long by about 2&nbsp;km wide and in excess of {{convert|10850|m|ft|0|abbr=on}} deep. In marked contrast to the ''Kairei'' surveys of 1998 and 1999, the detailed survey in 2002 determined that the deepest point in the Challenger Deep is located in the eastern basin around {{Coord|11|22.260|N|142|35.589|E}}, with a depth of {{convert|10920|±|5|m|ft|0|abbr=on}}, located about {{convert|290|m|abbr=on}} southeast of the deepest site determined by the survey vessel ''Takuyo'' in 1984. The 2002 surveys of both the western and eastern basins were tight, with especially meticulous cross-gridding of the eastern basin with ten parallel tracks N–S and E–W less than 250 meters apart. On the morning of 17 October, ROV ''Kaikō'' dive #272 began and recovered over 33 hours later, with the ROV working at the bottom of the western basin for 26 hours (vicinity of 11°20.148' N, 142°11.774 E at {{convert|10893|m|ft|0|abbr=on}}). Five ''Kaikō'' dives followed on a daily basis into the same area to service benthic landers and other scientific equipment, with dive #277 recovered on 25 October. Traps brought up large numbers of amphipods (sea fleas), and cameras recorded holothurians ([[sea cucumber]]s), White [[polychaete]]s (bristle worms), tube worms, and other biological species.<ref>[http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.332868380845,142.23056034137,14 DR02-13, Kaikō/Kairei Cruise in the Challenger Deep Onboard Report] {{Webarchive|url=https://web.archive.org/web/20210228060012/http://www.godac.jamstec.go.jp/darwin/mapsearch/e#11.332868380845,142.23056034137,14 |date=28 February 2021}}, input criteria "Kairei" and "KR02-13"</ref> During its 1998, 1999 surveys, ''Kairei'' was equipped with a GPS satellite-based [[Radionavigation-satellite service|radionavigation]] system. The United States government lifted the GPS selective availability in 2000, so during its 2002 survey, ''Kairei'' had access to non-degraded GPS positional services and achieved single-digit meter accuracy in geodetic positioning.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/>

===2001 – RV ''Melville''===
[[File:RV Melville (25635910745).jpg|thumb|The RV ''Melville'' was operated by the Scripps Institution of Oceanography.]]

The 2.516-ton research vessel [[BRP Gregorio Velasquez (AGR 702)|''Melville'']], at the time operated by the Scripps Institution of Oceanography, took the Cook Expedition, Leg 6 with chief scientist Patricia Fryer of the University of Hawaiʻi from Guam on 10 February 2001 to the Challenger Deep for a survey titled "Subduction Factory Studies in the Southern Mariana", including HMR-1 sonar mapping, magnetics, gravity measurements, and dredging in the Mariana arc region.<ref>{{cite web |url=https://www.nsf.gov/awardsearch/showAward?AWD_ID=9907063 |title=Subduction Factory Studies in the Southern Mariana Convergent Margin: Side-Scan, Geophysical and Petrologic Investigations |publisher=National Science Foundation |access-date=26 November 2019 |archive-date=27 July 2020 |archive-url=https://web.archive.org/web/20200727192713/https://www.nsf.gov/awardsearch/showAward?AWD_ID=9907063 |url-status=live}}</ref><ref>Patricia Fryer, [http://siox.sdsc.edu/search.php?xml=xqdl_0_1.xml&collectionidentifier_tag=COOK06MV&collectionidentifier=COOK06MV&subject_tag=&subject=&format=&adoidentifier=&creator_tag=&creator=&timestart=&timeend=&latitudenorth=&longitudewest=&longitudeeast=&latitudesouth=&action=Run+Search&results_type=1 Report and Index of Underway Marine Geophysical Data] {{Webarchive|url=https://web.archive.org/web/20211224210758/http://siox.sdsc.edu/search.php?xml=xqdl_0_1.xml&collectionidentifier_tag=COOK06MV&collectionidentifier=COOK06MV&subject_tag=&subject=&format=&adoidentifier=&creator_tag=&creator=&timestart=&timeend=&latitudenorth=&longitudewest=&longitudeeast=&latitudesouth=&action=Run+Search&results_type=1 |date=24 December 2021}}, Cook Expedition Leg 6, Scripps Institution of Oceanography; 2001</ref> They covered all three basins, then tracked {{convert|120|nmi|km|1|adj=mid|-long}} lines of bathymetry East-West, stepping northward from the Challenger Deep in {{convert|12|km|mi|abbr=on}} sidesteps, covering more than {{convert|90|nmi|km|1|abbr=on}} north into the backarc with overlapping swaths from their SeaBeam 2000 12&nbsp;kHz multi-beam echosounder and MR1 towed system. They also gathered [[geomagnetic|magnetic]] and [[gravity]] information, but no seismic data. Their primary survey instrument was the MR1 towed sonar,<ref>{{cite web |url=http://www.soest.hawaii.edu/HMRG/cms/ |title=Hawaii Mapping Research Group |publisher=University of Hawaiʻi |access-date=25 November 2019 |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415113648/http://www.soest.hawaii.edu/HMRG/cms/ |url-status=live}}</ref> a shallow-towed 11/12&nbsp;kHz bathymetric [[sidescan sonar]] developed and operated by the Hawaii Mapping Research Group (HMRG), a research and operational group within University of Hawaiʻi's School of Ocean and Earth Science and Technology (SOEST) and the Hawaii Institute of Geophysics and Planetology (HIGP). The MR1 is full-ocean-depth capable, providing both bathymetry and sidescan data.

Leg 7 of the Cook Expedition continued the MR-1 survey of the Mariana Trench backarc from 4 March to 12 April 2001 under chief scientist Sherman Bloomer of [[Oregon State University]].

===2009 – RV ''Kilo Moana''===
[[File:US Navy 090814-N-0000X-001 The Office of Naval Research small waterplane area twin-hull oceanographic research ship R-V Kilo Moana takes part in the second Radiance in a Dynamic Ocean (RaDyO) program.jpg|thumb|The RV ''Kilo Moana'' was used as the support ship of the HROV ''[[Nereus (underwater vehicle)|Nereus]]''.]]

In May/June 2009, the US Navy-owned 3,064-ton twin-hulled research vessel [[RV Kilo Moana (T-AGOR-26)|''Kilo Moana'' (T-AGOR 26)]] was sent to the Challenger Deep area to conduct research. ''Kilo Moana'' is civilian-crewed and operated by SOEST. It is equipped with two multibeam echosounders with sub-bottom profiler add-ons (the 191-beam 12&nbsp;kHz [[Kongsberg Gruppen|Kongsberg Simrad]] EM120 with SBP-1200, capable of accuracies of 0.2–0.5% of water depth across the entire swath), [[gravimeter]], and [[magnetometer]]. The EM-120 uses 1 by 1 degree sonar-emissions at the sea surface. Each 1 degree beam width sonar ping expands to cover a circular area about {{convert|192|m|ft}} in diameter at {{convert|11000|m|ft|0}} depth. Whilst mapping the Challenger Deep the sonar equipment indicated a maximum depth of {{convert|10971|m|0|abbr=on}} at an undisclosed position.<ref>{{cite web| url = https://epic.awi.de/id/eprint/29970/1/Kon2010a.pdf| title = Operators Manual, EM120 Multibeam Echosounder| access-date = 1 December 2019| archive-date = 29 September 2020| archive-url = https://web.archive.org/web/20200929021452/https://epic.awi.de/id/eprint/29970/1/Kon2010a.pdf| url-status = live}}</ref><ref name="Daily Reports for R/V KILO MOANA">{{Cite news|url=http://www.soest.hawaii.edu/UMC/cms/ship-daily-reports/|title=Daily Reports for R/V KILO MOANA June and July 2009|date=4 June 2009|publisher=University of Hawaiʻi Marine Center|access-date=4 June 2009|archive-date=31 December 2013|archive-url=https://web.archive.org/web/20131231001444/http://www.soest.hawaii.edu/UMC/cms/ship-daily-reports/}}</ref><ref name="Scientic Equipment aboard the R/V KILO MOANA">{{Cite news|url=http://www.soest.hawaii.edu/UMC/cms/kilo-moana/|title=Inventory of Scientific Equipment aboard the R/V KILO MOANA|date=4 June 2009|publisher=University of Hawaii Marine Center|access-date=4 June 2009|archive-date=24 February 2020|archive-url=https://web.archive.org/web/20200224214619/http://www.soest.hawaii.edu/UMC/cms/kilo-moana/|url-status=live}}</ref><ref>{{cite web|url=https://epic.awi.de/id/eprint/26725/1/Kon2007a.pdf |archive-url=https://web.archive.org/web/20191112152322/https://epic.awi.de/id/eprint/26725/1/Kon2007a.pdf |archive-date=2019-11-12 |url-status=live|title=Product description EM 120 Multibeam echo sounder|author=Kongsberg|website=www.epic.awi.de}}</ref> Navigation equipment includes the [[Applanix|Applanix POS MV320]] V4, rated at accuracies of 0.5–2&nbsp;m.<ref>Applanix_POS_MV_-_Datasheet.pdf www.mra.pt›repositorio›pdf›especificaciones-pos-mv-320</ref> RV ''Kilo Moana'' was also used as the support ship of the [[remotely operated underwater vehicle|hybrid remotely operated underwater vehicle]] (HROV) ''[[Nereus (underwater vehicle)|Nereus]]'' that dived three times to the Challenger Deep bottom during the May/June 2009 cruise and did not confirm the sonar established maximum depth by its support ship.

===2009 – RV ''Yokosuka''===
Cruise YK09-08 brought the JAMSTEC 4,429-ton research vessel ''Yokosuka'' back to the [[Mariana Trough]] and to the Challenger Deep June–July 2009. Their mission was a two-part program: surveying three [[hydrothermal vent]] sites in the southern Mariana Trough backarc basin near 12°57'N, 143°37'E about 130 nmi northeast of the central basin of the Challenger Deep, using the autonomous underwater vehicle ''Urashima''. AUV ''Urashima'' dives #90–94, were to a maximum depth of 3500 meters, and were successful in surveying all three sites with a Reson SEABAT7125AUV multibeam echosounder for bathymetry, and multiple water testers to detect and map trace elements spewed into the water from hydrothermal vents, white smokers, and hot spots. Kyoko OKINO from the Ocean Research Institute, University of Tokyo, was [[principal investigator]] for this aspect of the cruise.
The second goal of the cruise was to deploy a new "10K free fall camera system" called ''Ashura'', to sample sediments and biologics at the bottom of the Challenger Deep. The principal investigator at the Challenger Deep was Taishi Tsubouchi of JAMSTEC. The lander ''Ashura'' made two descents: on the first, 6 July 2009, ''Ashura'' bottomed at {{Coord|11|22.3130|N|142|25.9412|E}} at {{convert|10867|m|ft|0}}. The second descent (on 10 July 2009) was to {{Coord|11|22.1136|N|142|25.8547|E}} at {{convert|10897|m|ft|0}}. The 270&nbsp;kg ''Ashura'' was equipped with multiple baited traps, a HTDV video camera, and devices to recover sediment, water, and biological samples (mostly amphipods at the bait, and bacteria and fungus from the sediment and water samples).<ref>[http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk09-08/e yk09-08 Yokosuka Cruise Report YK09-08, Mariana Trough. June 29, 2009 – July 17, 2009] {{Webarchive|url=https://web.archive.org/web/20200727195052/http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk09-08/e |date=27 July 2020}} Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 31 July 2009 Yokosuka Cruise Report YK09-08</ref>

===2010 – USNS ''Sumner''===
On 7 October 2010, further sonar mapping of the Challenger Deep area was conducted by the US [[Center for Coastal & Ocean Mapping]]/Joint Hydrographic Center (CCOM/JHC) aboard the 4,762-ton [[USNS Sumner (T-AGS-61)|''Sumner'']]. The results were reported in December 2011 at the annual [[American Geophysical Union]] fall meeting. Using a Kongsberg Maritime EM 122 multi-beam echosounder system coupled to positioning equipment that can determine latitude and longitude up to {{convert|50|cm|in|abbr=on}} accuracy, from thousands of individual soundings around the deepest part the CCOM/JHC team preliminary determined that the Challenger Deep has a maximum depth of {{convert|10994|m|ft|abbr=on}} at {{Coord|11.326344|N|142.187248|E|scale:100000}}, with an estimated vertical uncertainty of ±{{convert|40|m|ft|0|abbr=on}} at two [[standard deviation]]s (i.e. ≈ 95.4%) confidence level.<ref name=BBC_CCOM>{{cite news |last= Amos |first= Jonathan |title= Oceans' deepest depth re-measured |url= https://www.bbc.co.uk/news/science-environment-15845550 |date= 7 December 2011 |work= BBC News |access-date= 7 December 2011 |archive-date= 2 December 2021 |archive-url= https://web.archive.org/web/20211202205859/https://www.bbc.co.uk/news/science-environment-15845550 |url-status= live}}</ref> A secondary deep with a depth of {{convert|10951|m|ft|abbr=on}} was located at approximately {{convert|23.75|nmi|km|1|abbr=on}} to the east at {{Coord|11.369639|N|142.588582|E|scale:100000}} in the eastern basin of the Challenger Deep.<ref name="2011 cruise report">{{cite web|url=http://ccom.unh.edu/sites/default/files/publications/Armstrong_2011_cruise_report_SU10-02_Marianas.pdf |archive-url=https://web.archive.org/web/20120526180857/http://ccom.unh.edu/sites/default/files/publications/Armstrong_2011_cruise_report_SU10-02_Marianas.pdf |archive-date=2012-05-26 |url-status=live |publisher=NOAA/UNH Joint Hydrographic Center University of New Hampshire |title=Cruise Report – UNH-CCOM/JHC Technical Report 11-002 |first=Andrew A. |last=Armstrong |page=12 |date=22 December 2011 |access-date=1 May 2012}}</ref><ref>{{cite web| url = http://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/01FB0F22974EA50FC125715E002B2143?OpenDocument| title = EM 122 Multibeam echosounder| access-date = 26 February 2013| archive-date = 6 November 2018| archive-url = https://web.archive.org/web/20181106235126/https://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/01FB0F22974EA50FC125715E002B2143?OpenDocument| url-status = live}}</ref><ref>{{cite web|url=http://www.km.kongsberg.com/ks/web/nokbg0397.nsf/AllWeb/E016DF00EBFC2964C12571B1003F9DDA/$file/306105aa_em122ds_lr.pdf?OpenElement|title=EM 122 sonar multibeam bathymetry system brochure|website=kongsberg.com|access-date=26 February 2013|archive-date=30 September 2021|archive-url=https://web.archive.org/web/20210930093430/https://www.kongsberg.com/km.kongsberg.com/ks/web/nokbg0397.nsf/AllWeb/E016DF00EBFC2964C12571B1003F9DDA/$file/306105aa_em122ds_lr.pdf?OpenElement}}</ref><ref>[http://www.ldeo.columbia.edu/res/pi/MB-System/formatdoc/EM_Datagram_Formats_RevP.pdf?OpenElement Instruction manual EM Series (EM 120 & EM 122) Multibeam echo sounders] {{webarchive|url=https://web.archive.org/web/20140102191111/http://www.ldeo.columbia.edu/res/pi/MB-System/formatdoc/EM_Datagram_Formats_RevP.pdf?OpenElement |date=2 January 2014}}</ref>

===2010 – RV ''Yokosuka''===
JAMSTEC returned ''Yokosuka'' to the Challenger Deep with cruise YK10-16, 21–28 November 2010. The chief scientist of this joint Japanese-Danish expedition was Hiroshi Kitazato of the Institute of Biogeosciences, JAMSTEC. The cruise was titled "Biogeosciences at the Challenger Deep: relict organisms and their relations to biogeochemical cycles". The Japanese teams made five deployments of their 11,000-meter camera system (three to 6,000 meters – two into the central basin of the Challenger Deep) which returned with 15 sediment cores, video records and 140 scavenging amphipod specimens. The Danish Ultra Deep Lander System was employed by Ronnie Glud et al on four casts, two into the central basin of the Challenger Deep and two to 6,000 m some 34 nmi west of the central basin. The deepest depth recorded was on 28 November 2010 – camera cast CS5 – {{Coord|11|21.9810|N|142|25.8680|E}}}, at a corrected depth of {{convert|10889.6|m|ft|0}} (the central basin).<ref>[http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-16/e *Biogeosciences at the Challenger Deep, the deepest point of the world: relict organisms and their relations to biogeochemical cycles"] {{Webarchive|url=https://web.archive.org/web/20191205062129/http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-16/e |date=5 December 2019}}, Preliminary Report for Yokosuka Cruise no. YK 10-16, Challenger Deep Mariana trench, Pacific Ocean, 20 November – 6 December 2010, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Cruise Report</ref>

===2013 – RV ''Yokosuka''===
With JAMSTEC Cruises YK13-09 and YK13-12, ''Yokosuka'' hosted chief scientist Hidetaka Nomaki for a trip to New Zealand waters (YK13-09), with the return cruise identified as YK13-12. The project name was QUELLE2013; and the cruise title was: "In situ experimental & sampling study to understand abyssal biodiversity and biogeochemical cycles". They spent one day on the return trip at the Challenger Deep to obtain DNA/RNA on the large amphipods inhabiting the Deep (''Hirondellea gigas''). Hideki Kobayashi (Biogeos, JAMSTEC) and the team deployed a benthic lander on 23 November 2013 with eleven baited traps (three bald, five covered by insulating materials, and three automatically sealed after nine hours) into the central basin of the Challenger Deep at {{Coord|11|21.9082|N|142|25.7606|E}}, depth {{convert|10896|m|ft|0}}. After an eight-hour, 46-minute stay at the bottom, they recovered some 90 individual ''Hirondellea gigas''.<ref>[http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk13-12/e "In situ experimental & sampling study to understand abyssal biodiversity and biogeochemical cycles, R/V Yokosuka Cruise Report YK13-12, In situ experimental & sampling study to understand abyssal biodiversity and biogeochemical cycles, western equatorial Pacific; 7–30 Nov 2013"] {{Webarchive|url=https://web.archive.org/web/20191205075159/http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk13-12/e |date=5 December 2019}}, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Cruise Report</ref>

[[File:JAMSTEC Deep Sea Research Ship Kairei P7224519.jpg|thumb|RV ''Kairei'' is used as the support ship for deep-diving ROVs.]]

===2014 – RV ''Kairei''===
JAMSTEC deployed ''Kairei'' to the Challenger Deep again 11–17 January 2014, under the leadership of chief scientist Takuro Nunora. The cruise identifier was KR14-01, titled: "Trench [[biosphere]] expedition for the Challenger Deep, Mariana Trench". The expedition sampled at six stations transecting the central basin, with only two deployments of the "11-K camera system" lander for sediment cores and water samples to "Station C" at the deepest depth, i.e. {{Coord|11|22.19429|N|142|25.7574|E}}, at {{convert|10903|m|ft|0}}. The other stations were investigated with the "Multi-core" lander, both to the backarc northward, and to the Pacific Plate southward. The 11,000-meter capable crawler-driven ROV ''ABIMSO'' was sent to 7,646 m depth about 20 nmi due north of the central basin (ABISMO dive #21) specifically to identify possible hydrothermal activity on the north slope of the Challenger Deep, as suggested by findings from ''Kairei'' cruise KR08-05 in 2008.<ref>Inoue, T. et.al, [https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf Crawler System for Deep Sea ROVs] {{Webarchive|url=https://web.archive.org/web/20190505025229/https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf |date=5 May 2019}}, ''Marine Technology Society Journal'', Winter 2009, Volume 43, Nunber 5, pages 97–104.</ref> ''AMISMO''{{'s}} dives #20 and #22 were to 7,900 meters about 15 nmi north of the deepest waters of the central basin. Italian researchers under the leadership of Laura Carugati from the [[Polytechnic University of Marche]], Italy (UNIVPM) were investigating the dynamics in virus/[[prokaryotes]] interactions in the Mariana Trench.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr14-01/e| title = RV Kairei Cruise Report, KR14-01, Trench biosphere expedition for the Challenger Deep, Mariana Trench, Jan 6–20, 2014| access-date = 7 December 2019| archive-date = 7 December 2019| archive-url = https://web.archive.org/web/20191207064257/http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr14-01/e| url-status = live}}</ref>

===2014 – RV ''Falkor''===
From 16–19 December 2014, the [[Schmidt Ocean Institute]]'s 2,024-ton research vessel ''[[RV Falkor|Falkor]]'', under chief scientist Douglas Bartlett from the Scripps Institution of Oceanography, deployed four different untethered instruments into the Challenger Deep for seven total releases. Four landers were deployed on 16 December into the central basin: the baited video-equipped lander ''Leggo'' for biologics; the lander ''ARI'' to {{Coord|11|21.5809|N|142|27.2969|E}} for water chemistry; and the probes ''Deep Sound 3'' and ''Deep Sound 2''. Both Deep Sound probes recorded acoustics floating at {{convert|9000|m|ft|0}} depth, until ''Deep Sound 3'' imploded at the depth of {{convert|8620|m|ft|0}} (about {{convert|2200|m|ft|0}} above the bottom) at {{Coord|11|21.99|N|142|27.2484|E}}.<ref>{{cite web| url = https://schmidtocean.org/wp-content/uploads/expanding-mariana-trench.pdf| title = Expanding Mariana Trench Perspectives Cruise Report| access-date = 29 November 2019| archive-date = 27 July 2020| archive-url = https://web.archive.org/web/20200727192756/https://schmidtocean.org/wp-content/uploads/expanding-mariana-trench.pdf| url-status = live}}</ref> The ''Deep Sound 2'' recorded the implosion of ''Deep Sound 3'', providing a unique recording of an implosion within the Challenger Deep depression. In addition to the loss of the ''Deep Sound 3'' by implosion, the lander ''ARI'' failed to respond upon receiving its instruction to drop weights, and was never recovered.<ref>{{cite web| url = https://docs.google.com/document/d/1jGu5hyJ3MDPoetvlhzwLWLUuWGBEEnHeVWSYJb1gCCs/| title = Bartlett, FK141215 Post Cruise Report, 11 January 2015| access-date = 29 November 2019| archive-date = 18 March 2023| archive-url = https://web.archive.org/web/20230318144847/https://docs.google.com/document/d/1jGu5hyJ3MDPoetvlhzwLWLUuWGBEEnHeVWSYJb1gCCs/edit| url-status = live}}</ref> On 16/17 December, ''Leggo'' was returned to the central basin baited for amphipods. On the 17th, RV ''Falkor'' relocated 17 nms eastward to the eastern basin, where they again deployed both the ''Leggo'' (baited and with its full camera load), and the ''Deep Sound 2''. ''Deep Sound 2'' was programmed to drop to {{convert|9000|m|ft|0}} and remain at that depth during its recording of sounds within the trench. On 19 December ''Leggo'' landed at {{Coord|11|22.11216|N|142|35.250996|E}} at a uncorrected depth of {{convert|11168|m|ft|0}} according to its pressure sensor readings. This reading was corrected to {{convert|10929|m|ft|0}} depth.<ref>{{cite web| url = https://schmidtocean.org/cruise/expanding-mariana-trench-perspectives/#data| title = Expanding Mariana Trench Perspectives| date = 21 December 2014| access-date = 29 November 2019| archive-date = 18 July 2019| archive-url = https://web.archive.org/web/20190718150954/https://schmidtocean.org/cruise/expanding-mariana-trench-perspectives/#data| url-status = live}}</ref><ref>{{cite web| url = https://drive.google.com/file/d/0B5irm_S0k8EEYnBZaHZZUW9KaE0/view?ths=true| title = FK141215 post cruise report 11 January 2015| access-date = 29 November 2019| archive-date = 17 May 2019| archive-url = https://web.archive.org/web/20190517050505/https://drive.google.com/file/d/0B5irm_S0k8EEYnBZaHZZUW9KaE0/view?ths=true| url-status = live}}</ref> ''Leggo'' returned with good photography of amphipods feeding on the lander's mackerel bait and with sample amphipods. ''Falknor'' departed the Challenger Deep on 19 December en route the [[Marianas Trench Marine National Monument]] to the Sirena Deep. RV ''Falkor'' had both a Kongsberg EM302 and EM710 multibeam echosounder for bathymetry, and an Oceaneering C-Nav 3050 global navigation satellite system receiver, capable of calculating geodetic positioning with an accuracy better than {{convert|5|cm|in|1|abbr=on}} horizontally and {{convert|15|cm|in|1|abbr=on}} vertically.<ref>{{cite web| url = https://www.oceaneering.com/positioning-solutions/| title = C-Nav® Positioning Solutions, Oceaneering International, Inc.| date = 9 May 2017| access-date = 29 November 2019| archive-date = 2 March 2020| archive-url = https://web.archive.org/web/20200302200613/https://www.oceaneering.com/positioning-solutions/| url-status = live}}</ref><ref>{{cite web| url = https://www.oceaneering.com/C-Nav/C-NavSupport/C-Nav3050/CNAV-MAN-017.9%20(C-Nav3050%20User%20Guide).pdf| title = C-Nav 3050 User Guide, Oceaneering International, Inc.| access-date = 29 November 2019| archive-date = 29 July 2020| archive-url = https://web.archive.org/web/20200729231416/https://www.oceaneering.com/C-Nav/C-NavSupport/C-Nav3050/CNAV-MAN-017.9%20(C-Nav3050%20User%20Guide).pdf| url-status = live}}</ref>

===2015 – USCGC ''Sequoia''===
[[File:USCGC Sequoia (WLB-215).jpg|thumb|US Coast Guard Cutter ''Sequoia'' (WLB 215)]]
From 10 to 13 July 2015, the Guam-based 1,930-ton US Coast Guard Cutter [[USCGC Sequoia (WLB-215)|''Sequoia'' (WLB 215)]] hosted a team of researchers, under chief scientist Robert P. Dziak, from the NOAA [[Pacific Marine Environmental Laboratory]] (PMEL), the [[University of Washington]], and Oregon State University, in deploying PMEL's "Full-Ocean Depth Mooring", a 45-meter-long moored deep-ocean [[hydrophone]] and pressure [[sensor array]] into the western basin of the Challenger Deep. A 6-hour descent into the western basin anchored the array at {{convert|10854.7|±|8.9|m|ft|0|abbr=on}} of water depth, at {{Coord|11|20.127|N|142|12.0233|E}}, about 1&nbsp;km northeast of ''Sumner''{{'s}} deepest depth, recorded in 2010.<ref>{{cite web |url=https://www.pmel.noaa.gov/acoustics/featured-publication/noaa-brings-back-first-recordings-deepest-part-ocean |last=Dziak |first=R. P. |display-authors=et al. |title=NOAA brings back first recordings from the deepest part of the ocean |date=16 May 2017 |access-date=22 December 2019 |archive-date=22 December 2019 |archive-url=https://web.archive.org/web/20191222160651/https://www.pmel.noaa.gov/acoustics/featured-publication/noaa-brings-back-first-recordings-deepest-part-ocean |url-status=live}}</ref> After 16 weeks, the moored array was recovered on 2–4 November 2015. "Observed sound sources included earthquake signals (T phases), baleen and odontocete cetacean vocalizations, ship propeller sounds, airguns, active sonar and the passing of a Category 4 typhoon." The science team described their results as "the first multiday, broadband record of ambient sound at Challenger Deep, as well as only the fifth direct depth measurement".<ref>{{cite journal |url=https://www.tos.org/oceanography/assets/docs/30-2_dziak.pdf |last=Dziak |first=Robert P. |display-authors=etal |title=Ambient Sound at Challenger Deep, Mariana Trench |journal=Oceanography |volume=30 |issue=2 |date=June 2017 |doi=10.5670/oceanog.2017.240 |bibcode=2017Ocgpy..30b.240D |access-date=22 December 2019 |archive-date=26 September 2020 |archive-url=https://web.archive.org/web/20200926113553/https://www.tos.org/oceanography/assets/docs/30-2_dziak.pdf |url-status=live}}</ref>

===2016 – RV ''Xiangyanghong 09''===
The 3,536-ton research vessel ''Xiangyanghong 09'' deployed on Leg II of the 37th China Cruise Dayang (DY37II) sponsored by the National Deep Sea Center, Qingdao and the Institute of Deep-Sea Science and Engineering, [[Chinese Academy of Sciences]] (Sanya, Hainan), to the Challenger Deep western basin area (11°22' N, 142°25' E) 4 June – 12 July 2016. As the mother ship for China's manned deep submersible [[Jiaolong (submersible)|''Jiaolong'']], the expedition carried out an exploration of the Challenger Deep to investigate the geological, biological, and chemical characteristics of the [[hadal zone]]. The diving area for this leg was on the southern slope of the Challenger Deep, at depths from about {{convert|6300|to|8300|m|ft|0}}. The submersible completed nine piloted dives on the northern backarc and south area ([[Pacific plate]]) of the Challenger Deep to depths from {{convert|5500|to|6700|m|ft|0}}. During the cruise, ''Jiaolong'' regularly deployed gas-tight samplers to collect water near the sea bottom. In a test of navigational proficiency, ''Jiaolong'' used an [[Ultra-short baseline|Ultra-Short Base Line]] (USBL) positioning system at a depth more than {{convert|6600|m|ft|0}} to retrieve sampling bottles.<ref>{{cite journal| url = http://www.chinaoceanengin.cn/article/app/id/0e93ec33-2c88-415e-90af-0597ab748385/flg| author = Xiang Gao |display-authors=etal |title=Target Deployment and Retrieval Using JIAOLONG Manned Submersible in the Depth of 6600 m in Mariana Trench |journal=China Ocean Engineering |year=2017 |volume=31 |issue=5 |pages=618–623| doi = 10.1007/s13344-017-0071-9 | bibcode = 2017ChOE...31..618G | s2cid = 116466712 |doi-access=free}}</ref>

===2016 – RV ''Tansuo 01''===
From 22 June to 12 August 2016 (cruises 2016S1 and 2016S2), the Chinese Academy of Sciences' 6,250-ton submersible support ship ''Tansuo 1'' (meaning: to explore) on her maiden voyage deployed to the Challenger Deep from her home port of Sanya, Hainan Island. On 12 July 2016, the ROV ''Haidou-1'' dived to a depth of {{convert|10767|m|ft|0}} in the Challenger Deep area. They also cast a free-drop lander, {{convert|9000|m|ft|0}} rated free-drop ocean-floor seismic instruments (deployed to {{convert|7731|m|ft|0}}), obtained sediment core samples, and collected over 2000 biological samples from depths ranging from {{convert|5000|to(-)|10000|m|ft|0}}.<ref>Wen-Li Li, et al., "Periodic and Spatial Spreading of Alkanes and Alcanivorax Bacteria in Deep Waters of the Mariana Trench", ''Applied and Environmental Microbiology'', January 2019, 85 (3)</ref> The ''Tansuo 01'' operated along the 142°30.00' longitude line, about 30 nmi east of the earlier DY37II cruise survey (see ''Xiangyanghong 09'' above).<ref>{{cite AV media| url = https://www.youtube.com/watch?v=yqIkbDK4VQY| title = What China's submersible mother ship takes back from Mariana Trench| people = New China TV| date = 26 August 2016| via = [[YouTube]]| access-date = 1 December 2019| archive-date = 26 April 2020| archive-url = https://web.archive.org/web/20200426115557/https://www.youtube.com/watch?v=yqIkbDK4VQY&gl=US&hl=en| url-status = live}}</ref>

===2016 – RV ''Sonne''===
[[File:RV Sonne 2014 1.jpg|thumb|German maritime [[research vessel]] ''Sonne'']]
In November 2016 sonar mapping of the Challenger Deep area was conducted by the [[Royal Netherlands Institute for Sea Research]] (NIOZ)/[[GEOMAR Helmholtz Centre for Ocean Research Kiel]] aboard the 8,554-ton Deep Ocean Research Vessel [[RV Sonne (2014)|''Sonne'']]. The results were reported in 2017. Using a Kongsberg Maritime EM 122 multi-beam echosounder system coupled to positioning equipment that can determine latitude and longitude the team determined that the Challenger Deep has a maximum depth of {{convert|10925|m|ft|abbr=on}} at {{Coord|11|19.945|N|142|12.123|E}} ({{Coord|11.332417|N|142.20205|E|scale:100000}}), with an estimated vertical uncertainty of ±{{convert|12|m|ft|0|abbr=on}} at one standard deviation (≈ 68.3%) confidence level. The analysis of the sonar survey offered a {{convert|100|by(x)|100|m|ft|0}} grid resolution at bottom depth, so small dips in the bottom that are less than that size would be difficult to detect from the 0.5 by 1 degree sonar-emissions at the sea surface. Each 0.5-degree beam width sonar ping expands to cover a circular area about {{convert|96|m|ft}} in diameter at {{convert|11000|m|ft|0}} depth.<ref>{{cite web| url = https://epic.awi.de/id/eprint/45364/1/Kongsberg_302440ae_em122_product_description.pdf| title = Product description Kongsberg Maritime EM 122 Multibeam Echo Sounder| access-date = 11 November 2019| archive-date = 11 November 2019| archive-url = https://web.archive.org/web/20191111093211/https://epic.awi.de/id/eprint/45364/1/Kongsberg_302440ae_em122_product_description.pdf| url-status = live}}</ref> The horizontal position of the grid point has an uncertainty of ±{{convert|50|to|100|m|ft|0|abbr=on}}, depending on along-track or across-track direction. This depth ({{convert|59|m|ft|0|abbr=on}}) and position (about {{convert|410|m|ft|0|abbr=on}} to the northeast) measurements differ significantly from the deepest point determined by the Gardner et al. (2014) study.<ref name="Ocean mixing in deep-sea trenches">{{cite web|url=http://tmp.hansvanharen.nl/pedef/2017DSRi.pdf |archive-url=https://web.archive.org/web/20190119174404/http://tmp.hansvanharen.nl/pedef/2017DSRi.pdf |archive-date=2019-01-19 |url-status=live|title=Ocean mixing in deep-sea trenches: New insights from the Challenger Deep, Mariana Trench. Deep-Sea Research, Part I. Oceanographic Research Papers, 129, 1–9|last1=van Haren |first1=H. |last2=Berndt |first2=C. |last3=Klaucke |first3=I. |date=2017|website=www.vliz.be}}</ref><ref name="RV SONNE 252 Cruise Report">{{cite web|url=https://www.portal-forschungsschiffe.de/lw_resource/datapool/_items/item_335/03g0252a_20170216_fahrtbericht.pdf |archive-url=https://web.archive.org/web/20181215173459/https://www.portal-forschungsschiffe.de/lw_resource/datapool/_items/item_335/03g0252a_20170216_fahrtbericht.pdf |archive-date=2018-12-15 |url-status=live|title=RV SONNE 252 Cruise Report / Fahrtbericht Yokohama: 05.11.2016 Nouméa: 18.12.2016 |author=Christian Berndt GEOMAR Helmholtz Centre for Ocean Research Kiel|date=2016|website=www.portal-forschungsschiffe.de}}</ref><ref name="RV SONNE 252 Cruise Report Raw Multibeam Data">{{cite book|title=Raw multibeam EM122 data: transits of SONNE cruise SO252 (Pacific). PANGAEA|last1=Berndt |first1=Christian |last2=Klaucke |first2=Ingo |last3=Wölfl |first3=Anne-Cathrin |date=2018|website=www.pangaea.de|doi=10.1594/PANGAEA.896077|type=Data Set|publisher=PANGAEA – Data Publisher for Earth & Environmental Science|chapter=Bathymetry}}</ref> The observed depth discrepancy with the 2010 sonar mapping and Gardner et al 2014 study are related to the application of differing sound velocity profiles, which are essential for accurate depth determination. ''Sonne'' used CTD casts about 1.6&nbsp;km west of the deepest sounding to near the bottom of the Challenger Deep that were used for [[Sound speed profile|sound velocity profile]] calibration and optimization. Likewise, the impact of using different projections, datum and ellipsoids during data acquisition can cause positional discrepancies between surveys.<ref name="Stewart, Heather & Jamieson, Alan. (2019)">{{cite journal |url=http://nora.nerc.ac.uk/id/eprint/524544/1/Stewart_and_Jamieson_2019_The%20five%20deeps.pdf |last1=Stewart |first1=Heather |last2=Jamieson |first2=Alan |year=2019 |title=The five deeps: The location and depth of the deepest place in each of the world's oceans |journal=Earth-Science Reviews |volume=197 |issue=197 |article-number=102896 |doi=10.1016/j.earscirev.2019.102896 |bibcode=2019ESRv..19702896S |s2cid=199113259 |access-date=15 October 2019 |archive-date=14 March 2020 |archive-url=https://web.archive.org/web/20200314064707/http://nora.nerc.ac.uk/id/eprint/524544/1/Stewart_and_Jamieson_2019_The%20five%20deeps.pdf |url-status=live}}</ref>

===2016 – RV ''Shyian 3''===
In December 2016, the CAS 3,300-ton research vessel ''Shiyan 3'' deployed 33 broadband seismometers onto both the backarc northwest of the Challenger Deep, and onto the near southern Pacific Plate to the southeast, at depths of up to {{convert|8137|m|ft|0|abbr=on}}. This cruise was part of a $12 million Chinese-U.S. initiative, led by co-leader Jian Lin of the [[Woods Hole Oceanographic Institution]]; a 5-year effort (2017–2021) to image in fine detail the rock layers in and around the Challenger Deep.<ref>{{cite journal |url= https://www.science.org/content/article/expedition-probes-ocean-trench-s-deepest-secrets |title= Expedition probes ocean trench's deepest secrets |first= Jane |last= Qiu |date= 11 January 2017 |journal= Science |volume= 355 |issue= 6321 |page= 115 |doi= 10.1126/science.355.6321.115 |pmid= 28082537 |access-date= 30 June 2022 |archive-date= 26 November 2022 |archive-url= https://web.archive.org/web/20221126210721/https://www.science.org/content/article/expedition-probes-ocean-trench-s-deepest-secrets |url-status= live |url-access= subscription}}</ref>

===2016 – RV ''Zhang Jian''===
The newly launched 4,800-ton research vessel (and mothership for the ''Rainbow Fish'' series of deep submersibles), the ''Zhang Jian'' departed [[Shanghai]] on 3 December. Their cruise was to test three new deep-sea landers, one uncrewed search submersible and the new ''Rainbow Fish'' 11,000-meter manned deep submersible, all capable of diving to 10,000 meters. From 25 to 27 December, three deep-sea landing devices descended into the trench. The first Rainbow Fish lander took photographs, the second took sediment samples, and the third took biological samples. All three landers reached over 10,000 meters, and the third device brought back 103 amphipods. Cui Weicheng, director of Hadal Life Science Research Center at [[Shanghai Ocean University]], led the team of scientists to carry out research at the Challenger Deep in the Mariana Trench. The ship is part of China's national marine research fleet but is owned by a Shanghai marine technology company.<ref>{{cite web| url = https://www.chinadailyasia.com/nation/2016-12/29/content_15549461.html| title = Unmanned submersibles descend 10,000 meters underwater| work = China Daily Asia| agency = Xinhua| date = 29 December 2016| access-date = 4 December 2019| archive-date = 4 December 2019| archive-url = https://web.archive.org/web/20191204034936/https://www.chinadailyasia.com/nation/2016-12/29/content_15549461.html| url-status = live}}</ref>

===2017 – RV ''Tansuo-1''===
CAS' Institute of Deep-sea Science and Engineering sponsored ''Tansuo-1''{{'s}} return to the Challenger Deep 20 January – 5 February 2017 (cruise TS03) with baited traps for the capture of fish and other macrobiology near the Challenger and Sirena Deeps. On 29 January they recovered photography and samples of a new species of snailfish from the Northern slope of the Challenger Deep at {{convert|7581|m|ft|0}}, newly designated ''Pseudoliparis swirei''.<ref name="Gerringer et al 2017">{{cite journal |url=https://biotaxa.org/Zootaxa/article/view/zootaxa.4358.1.7 |last1=Gerringer |first1=M. E. |last2=Linley |first2=T. D. |last3=Jamieson |first3=A. J. |last4=Goetze |first4=E. |last5=Drazen |first5=J. C. |year=2017 |title=Pseudoliparis swirei sp. nov.: A newly-discovered hadal snailfish (Scorpaeniformes: Liparidae) from the Mariana Trench |journal=Zootaxa |volume=4358 |issue=1 |pages=161–177 |doi=10.11646/zootaxa.4358.1.7 |pmid=29245485 |doi-access=free |access-date=2 December 2019 |archive-date=11 February 2020 |archive-url=https://web.archive.org/web/20200211022650/https://www.biotaxa.org/Zootaxa/article/view/zootaxa.4358.1.7 |url-status=live}}</ref> They also placed four or more CTD casts into the ''central'' and ''eastern'' basins of the Challenger Deep, as part of the World Ocean Circulation Experiment (WOCE).<ref>{{cite journal|title = Seasonal variability of water characteristics in the Challenger Deep observed by four cruises |author1=Caijing Huang |author2=Qiang Xie |author3=Dongxiao Wang |author4=Yeqiang Shu |author5=Hongzhou Xu |author6=Jingen Xiao |author7=Tingting Zu |author8=Tong Long |author9=Tiecheng Zhang |display-authors=6 |journal=Scientific Reports |volume=8 |number=11791 |year=2018|page = 11791 |doi = 10.1038/s41598-018-30176-4 |pmid = 30087355 |pmc = 6081482 |bibcode = 2018NatSR...811791H |s2cid = 51935374}}</ref>

===2017 – RV ''Shinyo Maru''===
[[Tokyo University of Marine Science and Technology]] dispatched the research vessel ''Shinyo Maru'' to the Mariana Trench from 20 January to 5 February 2017 with baited traps for the capture of fish and other macrobiology near the Challenger and Sirena Deeps. On 29 January they recovered photography and samples of a new species of snailfish from the Northern slope of the Challenger Deep at {{convert|7581|m|ft|0}}, which has been newly designated ''[[Pseudoliparis swirei]]''.<ref name="Gerringer et al 2017"/>

===2017 – RV ''Kexue 3''===
Water samples were collected at Challenger Deep from 11 layers of the Mariana Trench in March 2017. Seawater samples from 4 to 4,000 m were collected by Niskin bottles mounted to a Seabird SBE25 CTDs; whereas water samples at depths from 6,050 m to 8,320 m were collected by a self-designed acoustic-controlled full ocean depth water samplers. In this study, scientists studied the RNA of pico- and nano-plankton from the surface to the hadal zone.<ref>{{cite journal |author1=Ruoyu Guo |author2=Yantao Liang |author3=Yu Xin |author4=Long Wang |author5=Shanli Mou |author6=Chunjie Cao |author7=Ruize Xie |author8=Chuanlun Zhang |author9=Jiwei Tian |author10=Yongyu Zhang |display-authors=6 |title=Insight Into the Pico- and Nano-Phytoplankton Communities in the Deepest Biosphere, the Mariana Trench |journal=Frontiers in Microbiology |date=26 September 2018 |volume=9 |article-number=2289 |doi=10.3389/fmicb.2018.02289|pmid=30319587 |pmc=6168665 |doi-access=free}}</ref>

===2017 – RV ''Kairei''===
JAMSTEC deployed ''Kairei'' to the Challenger Deep in May 2017 for the express purpose of testing the new full-ocean depth ROV ''UROV11K'' (Underwater ROV 11,000-meter-capable), as cruise KR 17-08C, under chief scientist Takashi Murashima. The cruise title was: "Sea trial of a full depth ROV ''UROV11K'' system in the Mariana Trench". ''UROV11K'' carried a new [[4K resolution|4K High Definition]] video camera system, and new sensors to monitor the hydrogen-sulfide, methane, oxygen, and hydrogen content of the water. Unfortunately, on ''UROV11K''{{'s}} ascent from {{convert|10899|m|ft|0}} (at about 11°22.30'N 142°35.8 E, in the ''eastern'' basin) on 14 May 2017, the ROV's buoyancy failed at {{convert|5320|m|ft|0}} depth, and all efforts to retrieve the ROV were unsuccessful. The rate of descent and drift is not available, but the ROV bottomed to the east of the deepest waters of the eastern basin as revealed by the ship's maneuvering on 14 May. Murashima then directed the Kairei to a location about 35 nmi east of the eastern basin of the Challenger Deep to test a new "Compact Hadal Lander" which made three descents to depths from 7,498 to 8,178 m for testing the Sony 4K camera and for photography of fish and other macro-biologics.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr17-08c/e| title = R/V KAIREI Final Report, KR17-08C, Sea trial of a full depth ROV 'UROV11K' system in the Mariana Trench, 2017/05/05 – 2017/05/25.| access-date = 7 December 2019| archive-date = 7 December 2019| archive-url = https://web.archive.org/web/20191207233759/http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr17-08c/e| url-status = live}}</ref>

===2018 – RV ''Shen Kuo''===
On its maiden voyage, the 2,150-ton twin-hulled scientific research vessel ''Shen Kuo'' (also ''Shengkuo'', ''Shen Ko'', or ''Shen Quo''), departed Shanghai on 25 November 2018 and returned on 8 January 2019. They operated in the Mariana Trench area, and on 13 December tested a system of underwater navigation at a depth exceeding 10,000 metres, during a field trial of the ''Tsaihungyuy'' (ultra-short baseline) system. Project leader Tsui Veichen stated that, with the Tsaihungyuy equipment at depth, it was possible to obtain a signal and determine exact [[geolocation]]s. The research team from [[Shanghai Ocean University]] and [[Westlake University]] was led by Cui Weicheng, director of Shanghai Ocean University's Hadal Science and Technology Research Center (HSRC).{{citation needed|date=December 2019}}<ref>[Shanghai newspaper article to be adding ref here]</ref>
The equipment to be tested included a piloted submersible (not full ocean depth – depth achieved not available) and two deep-sea landers, all capable of diving to depths of 10,000 meters, as well as an ROV that can go to 4,500 meters. They took photographs and obtained samples from the trench, including water, sediment, macro-organisms and micro-organisms. Cui says, "If we can take photos of fish more than 8,145 meters under water, ... we will break the current world record. We will test our new equipment including the landing devices. They are second generation. The first generation could only take samples in one spot per dive, but this new second generation can take samples at different depths in one dive. We also tested the ultra short baseline acoustic positioning system on the manned submersible, the future of underwater navigation."{{citation needed|date=December 2019}}

===2019 – RV ''Sally Ride''===
[[File:R-V Sally Ride is currently underway conducting a series of science verification cruises. (31534416962).jpg|thumb|General Oceanographic RV ''Sally Ride'']]

In November 2019, as cruise SR1916, a NIOZ team led by chief scientist Hans van Haren, with [[Scripps Institution of Oceanography|Scripps]] technicians, deployed to the Challenger Deep aboard the 2,641-ton research vessel {{ship|RV|Sally Ride|AGOR-28|2}}, to recover a mooring line from the western basin of the Challenger Deep. The {{convert|7|km|mi|1|abbr=on}} long mooring line in the Challenger Deep consisted of top-floatation positioned around {{convert|4|km|mi|1|abbr=on}} depth, two sections of Dyneema neutrally buoyant {{convert|6|mm|in|1|abbr=on}} line, two Benthos acoustic releases and two sections of self-contained instrumentation to measure and store current, salinity and temperature. Around the {{convert|6|km|mi|1|abbr=on}} depth position two current meters were mounted below a {{convert|200|m|ft|0|abbr=on}} long array of 100 high-resolution temperature sensors. In the lower position starting {{convert|600|m|ft|0|abbr=on}} above the sea floor 295 specially designed high-resolution temperature sensors were mounted, the lowest of which was {{convert|8|m|ft|0|abbr=on}} above the trench floor. The mooring line was deployed and left by the NIOZ team during the November 2016 RV ''Sonne'' expedition with the intention to be recovered in late 2018 by ''Sonne''. The acoustic commanded release mechanism near the bottom of the Challenger Deep failed at the 2018 attempt. RV ''Sally Ride'' was made available exclusively for a final attempt to retrieve the mooring line before the release mechanism batteries expired.<ref name="hansvanharen.nl">{{cite report |url=http://www.hansvanharen.nl/publications/cruise-reports/ |last=van Haren |first=H. |year=2019 |title=Cruise report PAC16: R/V Sally Ride cruise SR1916, 31 October – 4 November 2019 |work=NIOZ |access-date=13 December 2019 |archive-date=13 December 2019 |archive-url=https://web.archive.org/web/20191213230321/http://www.hansvanharen.nl/publications/cruise-reports/ |url-status=live}}</ref> ''Sally Ride'' arrived at the Challenger Deep on 2 November. This time a 'deep release unit' lowered by one of ''Sally Ride''{{'s}} winch-cables to around 1,000 m depth pinged release commands and managed to contact the near-bottom releases. After being submerged for nearly three years, mechanical problems occurred in 15 of the 395 temperature sensors. The first results indicate the occurrence of [[internal wave]]s in the Challenger Deep.<ref>{{cite web| url = https://www.nioz.nl/en/news/successful-mooring-recovery-from-challenger-deep-mariana-trench| title = Successful mooring recovery from Challenger Deep (Mariana Trench)| work = NIOZ| date = 29 November 2019| access-date = 30 November 2019| archive-date = 8 December 2019| archive-url = https://web.archive.org/web/20191208075523/https://www.nioz.nl/en/news/successful-mooring-recovery-from-challenger-deep-mariana-trench| url-status = live}}</ref><ref>{{cite journal| url = https://www.sciencedirect.com/science/article/pii/S0967063720301874| title = Challenger Deep internal wave turbulence events| journal = Hans van Haren| date = 13 September 2020| doi = 10.1016/j.dsr.2020.103400| access-date = 24 July 2022| archive-date = 24 July 2022| archive-url = https://web.archive.org/web/20220724184521/https://www.sciencedirect.com/science/article/pii/S0967063720301874| url-status = live| last1 = Van Haren| first1 = Hans| volume = 165| article-number = 103400| arxiv = 2007.13409| bibcode = 2020DSRI..16503400V| s2cid = 220793648}}</ref>

==Study of the depth and location of the Challenger Deep==
Since May 2000, with the help of non-degraded signal [[satellite navigation]], civilian surface vessels equipped with professional dual-frequency capable satellite navigation equipment can measure and establish their geodetic position with an accuracy in the order of meters to tens of meters whilst the western, central and eastern basins are kilometers apart.<ref>{{cite web|url=https://www.gps.gov/systems/gps/performance/accuracy/|title=GPS.gov: GPS Accuracy|website=www.gps.gov|language=en|access-date=2018-01-17|archive-url=https://web.archive.org/web/20180104171609/https://www.gps.gov/systems/gps/performance/accuracy/|archive-date=4 January 2018|url-status=live}}</ref>

[[File:GEBCO 2019 bathymetry Challenger Deep and Sirena Deep.jpg|thumb|upright=1.75|GEBCO 2019 bathymetry of the Challenger Deep and [[Sirena Deep]].<br />(a) Mariana Trench multibeam bathymetry data gridded at 75 m acquired on-board the DSSV Pressure Drop overtop the GEBCO 2019 source grid (as shown in Figure 1) and the complete GEBCO 2019 grid with hillshade. EM 124 black contours at 500 m intervals, GEBCO 2019 grey contours at 1,000 m intervals. The white circle indicates the deepest point and submersible dive location, the white triangle indicates the submersible dive location from Sirena Deep, the red spot was the deepest point derived by van Haren et al., (2017).<br />
(b) Challenger Deep.<br />
(c) Sirena Deep.<br />
Bathymetric cross sections A'–A" and B'–B" over Challenger Deep and Sirena Deep displayed in (d) and (e), respectively.]]

In 2014, a study was conducted regarding the determination of the depth and location of the Challenger Deep based on data collected previous to and during the 2010 sonar mapping of the Mariana Trench with a Kongsberg Maritime EM 122 multibeam echosounder system aboard USNS ''Sumner''. This study by James. V. Gardner et al. of the Center for Coastal & Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean Engineering Laboratory of the University of New Hampshire splits the measurement attempt history into three main groups: early single-beam echo sounders (1950s–1970s), early multibeam echo sounders (1980s – 21st century), and modern (i.e., post-GPS, high-resolution) multibeam echo sounders. Taking uncertainties in depth measurements and position estimation into account, the raw data of the 2010 bathymetry of the Challenger Deep vicinity consisting of 2,051,371 soundings from eight survey lines was analyzed. The study concludes that with the best of 2010 multibeam echosounder technologies after the analysis a depth uncertainty of ±{{convert|25|m|ft|0|abbr=on}} (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ±{{convert|20|to|25|m|ft|0|abbr=on}} ([[Circular error probable|2drms]]) remain and the location of the deepest depth recorded in the 2010 mapping is {{convert|10984|m|ft|abbr=on}} at {{Coord|11.329903|N|142.199305|E|scale:100000}}. The depth measurement uncertainty is a composite of measured uncertainties in the spatial variations in sound-speed through the water volume, the ray-tracing and bottom-detection algorithms of the multibeam system, the accuracies and calibration of the motion sensor and navigation systems, estimates of spherical spreading, attenuation throughout the water volume, and so forth.<ref name="So, How Deep Is the Mariana Trench?">{{cite web |url=http://ccom.unh.edu/sites/default/files/publications/Gardner-et-al-2014-Challenger-Deep.pdf |title=So, How Deep Is the Mariana Trench? |date=5 March 2014 |publisher=Center for Coastal & Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean Engineering Laboratory of the University of New Hampshire |access-date=20 May 2014 |archive-date=21 May 2014 |archive-url=https://web.archive.org/web/20140521032157/http://ccom.unh.edu/sites/default/files/publications/Gardner-et-al-2014-Challenger-Deep.pdf |url-status=live}}</ref>

Both the RV ''Sonne'' expedition in 2016, and the RV ''Sally Ride'' expedition in 2019 expressed strong reservations concerning the depth corrections applied by the Gardner et al. study of 2014, and serious doubt concerning the accuracy of the deepest depth calculated by Gardner (in the ''western'' basin), of {{convert|10984|m|ft|abbr=on}} after analysis of their multibeam data on a {{convert|100|m|ft|0|abbr=on}} grid. Dr. Hans van Haren, chief scientist on the RV ''Sally Ride'' cruise SR1916, indicated that Gardner's calculations were {{convert|69|m|ft|abbr=on}} too deep due to the "sound velocity profiling by Gardner et al. (2014)."<ref name="hansvanharen.nl"/>

In 2018-2019, the deepest points of each ocean were mapped using a full-ocean depth Kongsberg EM 124 multibeam echosounder aboard ''DSSV Pressure Drop''. In 2021, a data paper was published by Cassandra Bongiovanni, Heather A. Stewart and Alan J. Jamieson regarding the gathered data donated to GEBCO. The deepest depth recorded in the 2019 Challenger Deep sonar mapping was {{convert|10924|m|ft|abbr=on}} ±{{convert|15|m|ft|0|abbr=on}} at {{Coord|11.369|N|142.587|E|scale:100000}} in the eastern basin. This depth closely agrees with the deepest point ({{convert|10925|m|ft|abbr=on}} ±{{convert|12|m|ft|0|abbr=on}}) determined by the Van Haren et al. sonar bathymetry. The geodetic position of the deepest depth according to the Van Haren et al. significantly differs (about {{convert|42|km|mi|abbr=on}} to the west) with the 2021 paper. After post-processing the initial depth estimates by application of a full-ocean depth sound velocity profile Bongiovanni et al. report an (almost) as deep point at {{Coord|11.331|N|142.205|E|scale:100000}} in the western basin that geodetically differs about {{convert|350|m|ft|abbr=on}} with the deepest point position determined by Van Haren et al. ({{Coord|11.332417|N|142.20205|E|scale:100000}} in the western basin). After analysis of their multibeam data on a {{convert|75|m|ft|0|abbr=on}} grid, the Bongiovanni et al. 2021 paper states the technological accuracy does not currently exist on low-frequency ship-mounted sonars required to determine which location was truly the deepest, nor does it currently exist on deep-sea pressure sensors.<ref name="202100505RMS">{{cite journal|title=High-resolution multibeam sonar bathymetry of the deepest place in each ocean |date=2021-05-05 |publisher=Royal Meteorological Society |doi=10.1002/gdj3.122 |last1=Bongiovanni |first1=Cassandra |last2=Stewart |first2=Heather A. |last3=Jamieson |first3=Alan J. |journal=Geoscience Data Journal |volume=9 |issue=1 |pages=108–123 |doi-access=free}}</ref>

In 2021, a study by Samuel F. Greenaway, [[Kathryn D. Sullivan]], Samuel H. Umfress, Alice B. Beittel and Karl D. Wagner was published presenting a revised estimate of the maximum depth of the Challenger Deep based on a series of submersible dives conducted in June 2020. These depth estimates are derived from acoustic echo sounding profiles referenced to in-situ direct pressure measurements and corrected for observed oceanographic properties of the water-column, atmospheric pressure, gravity and gravity-gradient anomalies, and water-level effects. The study concludes according to their calculations the deepest observed seafloor depth was {{convert|10935|m|ft|abbr=on}} ±{{convert|6|m|ft|0|abbr=on}} below mean sea level at a 95% confidence level at {{Coord|11|22.3|N|142|35.3|E}} in the eastern basin. For this estimate, the error term is dominated by the uncertainty of the employed pressure sensor, but Greenaway et al. show that the gravity correction is also substantial. The Greenaway et al. study compares its results with other recent acoustic and pressure-based measurements for the Challenger Deep and concludes the deepest depth in the western basin is very nearly as deep as the eastern basin. The disagreement between the maximum depth estimates and their geodetic positions between post-2000 published depths however exceed the accompanying margins of uncertainty, raising questions regarding the measurements or the reported uncertainties.<ref name="20211021ORP">{{cite journal|title=Revised depth of the Challenger Deep from submersible transects; including a general method for precise, pressure-derived depths in the ocean |date=2021-10-21 |publisher=NOAA, Potomac Institute |doi=10.1016/j.dsr.2021.103644 |last1=Greenaway |first1=Samuel F. |last2=Sullivan |first2=Kathryn D. |last3=Beittel |first3=Alice B. |last4=Wagner |first4=Karl D. |last5=Umfress |first5=Samuel H. |journal=Oceanographic Research Papers |volume=178 |article-number=103644 |bibcode=2021DSRI..17803644G |doi-access=free}}</ref>

Another 2021 paper by Scott Loranger, David Barclay and Michael Buckingham, besides a December 2014 implosion shock wave based depth estimate of {{convert|10983|m|ft|abbr=on}}, which is among the deepest estimated depths, also treatises the differences between various maximum depth estimates and their geodetic positions.<ref name="20210419TOS">{{cite journal |url=https://tos.org/oceanography/article/implosion-in-the-challenger-deep-echo-sounding-with-the-shock-wave |title=Implosion in the Challenger Deep: Echo Sounding with the Shock Wave |date=2021-04-19 |publisher=The Oceanography Society |doi=10.5670/oceanog.2021.201 |issn=1042-8275 |access-date=2021-11-04 |last1=Loranger |first1=Scott |last2=Berclay |first2=David |last3=Buckingham |first3=Michael |journal=Oceanography |volume=34 |issue=2 |doi-access=free |bibcode=2021Ocgpy..34b.201L |archive-date=4 November 2021 |archive-url=https://web.archive.org/web/20211104120149/https://tos.org/oceanography/article/implosion-in-the-challenger-deep-echo-sounding-with-the-shock-wave |url-status=live |hdl=1912/27739 |hdl-access=free}}</ref><ref name="20220208NG">{{cite web |url=https://www.nationalgeographic.com/science/article/accidental-implosion-yields-new-measurement-for-oceans-deepest-point |title=Accidental implosion yields new measurement for ocean's deepest point |date=2022-02-08 |publisher=National Geographic Society |access-date=2022-02-09 |last1=Wei-Haas |first1=Maya |archive-date=9 February 2022 |archive-url=https://web.archive.org/web/20220209191833/https://www.nationalgeographic.com/science/article/accidental-implosion-yields-new-measurement-for-oceans-deepest-point}}</ref>

===Direct measurements===
The 2010 maximal sonar mapping depths reported by Gardner et al. in 2014 and Greenaway et al. study in 2021 have not been confirmed by direct descent (pressure gauge/manometer) measurements at full-ocean depth.<ref>{{cite web |url=http://ccom.unh.edu/sites/default/files/publications/Gardner-et-al-2014-Challenger-Deep.pdf |title=So, How Deep Is the Mariana Trench? |date=5 March 2014 |publisher=Center for Coastal & Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean Engineering Laboratory of the University of New Hampshire |access-date=20 May 2014 |archive-date=21 May 2014 |archive-url=https://web.archive.org/web/20140521032157/http://ccom.unh.edu/sites/default/files/publications/Gardner-et-al-2014-Challenger-Deep.pdf |url-status=live}}</ref> Expeditions have reported direct measured maximal depths in a narrow range.

*For the '''''western'' basin''' deepest depths were reported as {{convert|10913|m|ft|abbr=on}} by {{ship|Bathyscaphe|Trieste||2}} in 1960 and {{Convert|10923|m|ft|abbr=on}} ±{{Convert|4|m|ft|abbr=on}} by ''[[DSV Limiting Factor]]'' in June 2020.
*For the '''''central'' basin''' the greatest reported depth is {{Convert|10915|m|ft|abbr=on}} ±{{Convert|4|m|ft|abbr=on}} by ''DSV Limiting Factor'' in June 2020.
*For the '''''eastern'' basin''' deepest depths were reported as {{convert|10911|m|ft|abbr=on}} by [[Kaikō ROV]] in 1995, {{convert|10902|m|ft|abbr=on}} by [[Nereus (underwater vehicle)|ROV ''Nereus'']] in 2009, {{convert|10908|m|ft|abbr=on}} by {{ship||Deepsea Challenger}} in 2012, {{convert|10929|m|ft|abbr=on}} by [[benthic lander]] "Leggo" in May 2019, and {{Convert|10925|m|ft|abbr=on}} ±{{Convert|4|m|ft|abbr=on}} by ''DSV Limiting Factor'' in May 2019.

==Descents==
===Manned descents===
[[File: Bathyscaphe Trieste.jpg|thumb|Bathyscaphe ''Trieste''. The spherical crew cabin is attached to the underside of a tank filled with gasoline (which is incompressible), which serves as a float giving the craft buoyancy.]]
[[File: Bathyscaphe Trieste Piccard-Walsh.jpg|thumb|upright|Lt. Don Walsh, USN (bottom) and Jacques Piccard (middle) in the ''Trieste'']]

====1960 – ''Trieste''====
{{Main|Bathyscaphe Trieste}}
On 23 January 1960, the Swiss-designed [[Bathyscaphe Trieste|''Trieste'']], originally built in Italy and acquired by the [[United States Navy|U.S. Navy]], supported by the USS ''Wandank'' (ATF 204) and escorted by the USS ''Lewis'' (DE 535), descended to the ocean floor in the trench piloted by [[Jacques Piccard]] (who co-designed the submersible along with his father, [[Auguste Piccard]]) and USN Lieutenant [[Don Walsh]]. Their crew compartment was inside a spherical pressure vessel – measuring 2.16 metres in diameter suspended beneath a buoyancy tank 18.4 metres in length<ref name=":0">{{Cite web|url=https://www.smh.com.au/environment/descent-to-challenger-deep-20110413-1ddnq.html|title=Descent to Challenger Deep|last=Kwek|first=Glenda|date=13 April 2011|website=The Sydney Morning Herald|language=en|access-date=31 July 2019|archive-date=31 July 2019|archive-url=https://web.archive.org/web/20190731175727/https://www.smh.com.au/environment/descent-to-challenger-deep-20110413-1ddnq.html|url-status=live}}</ref> – which was a heavy-duty replacement (of the Italian original) built by [[Krupp]] Steel Works of [[Essen]], Germany. The steel walls were {{cvt|12.7|cm|in}} thick and designed to withstand pressure of up to {{convert|1250|kg/cm2|psi atm MPa|abbr=out|comma=off}}.<ref name=":0" />
Their descent took almost five hours and the two men spent barely twenty minutes on the ocean floor before undertaking the three-hour-and-fifteen-minute ascent. Their early departure from the [[Seabed|ocean floor]] was due to their concern over a crack in the outer window caused by the temperature differences during their descent.<ref name="National Geographics">{{cite web |url=http://deepseachallenge.com/the-expedition/1960-dive/ |title=1960 Dive - DEEPSEA CHALLENGE Expedition |access-date=10 April 2012 |archive-url=https://web.archive.org/web/20120414093239/http://deepseachallenge.com/the-expedition/1960-dive/ |archive-date=14 April 2012}}</ref>

''Trieste'' dived at/near {{Coord|11|18.5|N|142|15.5|E}}, bottoming at {{convert|10911|m|ft}} ±{{convert|7|m|ft|0|abbr=on}} into the Challenger Deep's ''western'' basin, as measured by an onboard [[manometer]].<ref>Piccard, J. "Seven Miles Deep," ''G.P. Putnam's Sons'', 1961, page 242</ref> Another source states the measured depth at the bottom was measured with a [[manometer]] at {{convert|10913|m|0|abbr=on}} ±{{convert|5|m|ft|0|abbr=on}}.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep" /><ref name="usn1960">{{cite web
|author=Press Release, Office of Naval Research
|date=1 February 1960
|url=http://www.onr.navy.mil/focus/ocean/vessels/submersibles11.htm
|title=Research Vessels: Submersibles – ''Trieste''
|publisher=United States Navy
|access-date=16 May 2010
|archive-url=https://web.archive.org/web/20020418105908/http://www.onr.navy.mil/focus/ocean/vessels/submersibles11.htm
|archive-date=18 April 2002}}</ref>
Navigation of the support ships was by celestial and [[LORAN-C]] with an accuracy of {{convert|460|m|ft}} or less.<ref name="jproc.ca"/> Fisher noted that the ''Trieste'''s reported depth "agrees well with the sonic sounding."<ref>Fisher, Trenches, ''The Earth Beneath the Sea'', page 416</ref>

====2012 – ''Deepsea Challenger''====
{{main|Deepsea Challenger}}
[[File:Deepsea Challenger Panorama.jpg|thumb|DSV ''Deepsea Challenger'']]
On 26 March 2012 (local time), Canadian film director [[James Cameron]] made a solo descent in the [[deep submergence vehicle|DSV]] ''Deepsea Challenger'' to the bottom of the Challenger Deep.<ref name="NGS-20120325">{{cite web|last=Than|first=Ker|title=James Cameron Completes Record-Breaking Mariana Trench Dive|url=http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-challenger-deepest-returns-science-sub/|date=25 March 2012|publisher=[[National Geographic Society]]|access-date=25 March 2012|archive-date=16 May 2019|archive-url=https://web.archive.org/web/20190516231005/https://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-challenger-deepest-returns-science-sub/}}</ref><ref name="NYT-20120325">{{cite news |last=Broad|first=William J. |title=Filmmaker in Submarine Voyages to Bottom of Sea|url=https://www.nytimes.com/2012/03/26/science/james-camerons-submarine-trip-to-challenger-deep.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2012/03/26/science/james-camerons-submarine-trip-to-challenger-deep.html |archive-date=2022-01-01 |url-access=limited|date=25 March 2012 |work=[[The New York Times]] |access-date=25 March 2012}}{{cbignore}}</ref><ref name="MSNBC-20120325">{{cite web |author=AP Staff |title=James Cameron has reached deepest spot on Earth |url=https://www.nbcnews.com/id/wbna46850002 |date=25 March 2012 |work=[[NBC News]] |access-date=25 March 2012 |archive-date=30 September 2020 |archive-url=https://web.archive.org/web/20200930203233/http://www.nbcnews.com/id/46850002 |url-status=live}}</ref><ref>{{cite news|last=Prince |first=Rosa |url=https://www.telegraph.co.uk/news/worldnews/australiaandthepacific/guam/9166425/James-Cameron-becomes-first-solo-diver-to-visit-Earths-deepest-point.html |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/worldnews/australiaandthepacific/guam/9166425/James-Cameron-becomes-first-solo-diver-to-visit-Earths-deepest-point.html |archive-date=11 January 2022 |url-access=subscription |url-status=live |title=James Cameron becomes first solo diver to visit Earth's deepest point |newspaper=The Telegraph |date=25 March 2012 |access-date=26 March 2012}}{{cbignore}}</ref>
At approximately 05:15 [[ChST]] on 26 March (19:15 UTC on 25 March), the descent began.<ref name="James Cameron Begins Descent to Ocean's Deepest Point">{{cite web |author=National Geographic |title=James Cameron Begins Descent to Ocean's Deepest Point |url=http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-dive-deepest-science-sub-descent/ |date=25 March 2012 |publisher=National Geographic Society |access-date=25 March 2012 |archive-date=27 March 2012 |archive-url=https://web.archive.org/web/20120327014617/http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-dive-deepest-science-sub-descent/}}</ref>
At 07:52 ChST (21:52 UTC), ''Deepsea Challenger'' arrived at the bottom. The descent lasted 2 hours and 36 minutes and the recorded depth was {{convert|10908|m|ft}} when ''Deepsea Challenger'' touched down.<ref name="James Cameron Now at Ocean's Deepest Point">{{cite web |author=National Geographic |title=James Cameron Now at Ocean's Deepest Point |url=http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-challenger-deep-deepest-science-sub/ |date=25 March 2012 |publisher=National Geographic Society |access-date=25 March 2012 |archive-date=27 March 2012 |archive-url=https://web.archive.org/web/20120327053619/http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-challenger-deep-deepest-science-sub/}}</ref>
Cameron had planned to spend about six hours near the ocean floor exploring but decided to start the ascent to the surface after only 2 hours and 34 minutes.<ref name="Cameron's Historic Dive Cut Short by Leak; Few Signs of Life Seen">{{cite web |author=National Geographic |title=Cameron's Historic Dive Cut Short by Leak; Few Signs of Life Seen |url=http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-fluid-leak-fish-science-sub/ |date=26 March 2012 |publisher=National Geographic Society |access-date=26 March 2012 |archive-date=28 March 2012 |archive-url=https://web.archive.org/web/20120328060000/http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-fluid-leak-fish-science-sub/}}</ref> The time on the bottom was shortened because a hydraulic fluid leak in the lines controlling the manipulator arm obscured the visibility out of the only viewing port. It also caused the loss of the submersible's starboard thrusters.<ref name="Problems at the bottom">{{cite web |author=National Geographic |title=Cameron's Historic Dive Cut Short by Leak; Few Signs of Life Seen |url=http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-fluid-leak-fish-science-sub/ |date=28 March 2012 |publisher=National Geographic Society |access-date=28 March 2012 |archive-date=28 March 2012 |archive-url=https://web.archive.org/web/20120328060000/http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-fluid-leak-fish-science-sub/}}</ref> At around 12:00 ChST (02:00 UTC on 26 March), the Deepsea Challenger website says the sub resurfaced after a 90-minute ascent,<ref name="We Just Did the Impossible">{{cite web |author=deepseachallenge.com |title=We Just Did the Impossible |url=http://deepseachallenge.com/expedition-journal/we-just-did-the-impossible/ |date=25 March 2012 |publisher=deepseachallenge.com |access-date=26 March 2012 |archive-url=https://web.archive.org/web/20120329093127/http://deepseachallenge.com/expedition-journal/we-just-did-the-impossible/ |archive-date=29 March 2012}}</ref> although [[Paul Allen]]'s tweets indicate the ascent took only about 67 minutes.<ref>{{cite tweet|number=184097111770529793|user=PaulGAllen|title=#deepseachallenge has surfaced, now for recovery...<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=22 July 2022|date=26 March 2012}}</ref> During a post-dive press conference Cameron said: "I landed on a very soft, almost gelatinous flat plain. Once I got my bearings, I drove across it for quite a distance ... and finally worked my way up the slope." The whole time, Cameron said, he didn't see any fish, or any living creatures more than an inch (2.54&nbsp;cm) long: "The only free swimmers I saw were small [[amphipods]]" – shrimplike bottom-feeders.<ref name="James Cameron on Earth's Deepest Spot: Desolate, Lunar-Like">{{cite web |author=National Geographic |title=James Cameron on Earth's Deepest Spot: Desolate, Lunar-Like |url=http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-challenger-deepest-lunar-sub-science/ |date=27 March 2012 |publisher=National Geographic Society |access-date=27 March 2012 |archive-date=28 March 2012 |archive-url=https://web.archive.org/web/20120328064958/http://news.nationalgeographic.com/news/2012/03/120326-james-cameron-mariana-trench-challenger-deepest-lunar-sub-science/}}</ref>

====2019 – ''Five Deeps Expedition / DSV Limiting Factor''====
{{main|DSV Limiting Factor}}
[[File:Limiting Factor to be prepared for a dive into the Atlantic Ocean.jpg|thumb|DSSV ''Pressure Drop'' and DSV ''Limiting Factor'' at its stern]]
[[File:Skaf and Closp shortly before a launch.jpg|thumb|The landers ''Skaff'' and ''Closp'' are prepared for a deployment during the Five Deeps Expedition.|alt=]]

The Five Deeps Expedition's objective was to thoroughly map and visit the deepest points of all five of the world's oceans by the end of September 2019.<ref>{{cite web|url=https://fivedeeps.com/|title=Home|website=fivedeeps.com|access-date=9 January 2019|archive-date=11 January 2019|archive-url=https://web.archive.org/web/20190111180529/https://fivedeeps.com/|url-status=live}}</ref> On 28 April 2019, explorer [[Victor Vescovo]] descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor'' (a [[Triton Submarines|Triton]] 36000/2 model submersible).<ref>{{cite web |url=https://fivedeeps.com/home/technology/sub/ |title=Full Ocean Depth Submersible LIMITING FACTOR |work=fivedeeps.com |access-date=18 May 2019 |archive-date=14 May 2019 |archive-url=https://web.archive.org/web/20190514014338/https://fivedeeps.com/home/technology/sub/ |url-status=live}}</ref><ref name="BBC News">{{cite news |url=https://www.bbc.co.uk/news/science-environment-48230157 |title=Mariana Trench: Deepest-ever sub dive finds plastic bag |work=BBC News |date=13 May 2019 |access-date=13 May 2019 |archive-date=13 May 2019 |archive-url=https://web.archive.org/web/20190513141623/https://www.bbc.co.uk/news/science-environment-48230157 |url-status=live}}</ref> Between 28 April and 4 May 2019, the ''Limiting Factor'' completed four dives to the bottom of Challenger Deep. The fourth dive descended to the slightly less deep "Central Pool" of the Challenger Deep (crew: Patrick Lahey, Pilot; John Ramsay, Sub Designer). The Five Deeps Expedition estimated maximum depths of {{Convert|10927|m|ft|abbr=on}} ±{{Convert|8|m|ft|abbr=on}} and {{Convert|10928|m|ft|abbr=on}} ±{{Convert|10.5|m|ft|abbr=on}} at ({{Coord|11.3693|N|142.5889|E|scale:100000}}) by direct [[CTD (instrument)|CTD]] pressure measurements and a survey of the operating area by the support ship, the Deep Submersible Support Vessel ''[[USNS Indomitable (T-AGOS-7)|DSSV ''Pressure Drop'']]'', with a Kongsberg SIMRAD EM124 multibeam echosounder system. The CTD measured pressure at {{Convert|10928|m|ft|abbr=on}} of seawater depth was {{convert|1126.79|bar|MPa psi|abbr=on}}.<ref>{{cite web|url=https://fivedeeps.com/home/technology/sub/certification/|title=Full Ocean Depth Submersible DNV-GL CERTIFICATION|work=fivedeeps.com|access-date=4 May 2019|archive-date=3 November 2019|archive-url=https://web.archive.org/web/20191103145726/https://fivedeeps.com/home/technology/sub/certification/|url-status=live}}</ref><ref name="ioc-unesco.org">{{cite web|url=http://ioc-unesco.org/index.php?option=com_oe&task=viewDocumentRecord&docID=3939|title=UNESCO Technical Papers in Marine Science 44, Algorithms for computation of fundamental properties of seawater|work=ioc-unesco.org|date=1983|access-date=9 November 2019|archive-date=27 July 2020|archive-url=https://web.archive.org/web/20200727192427/http://ioc-unesco.org/index.php?option=com_oe&task=viewDocumentRecord&docID=3939|url-status=live}}</ref> Due to a technical problem the (uncrewed) [[benthic lander|ultra-deep-sea lander ''Skaff'']] used by the Five Deeps Expedition stayed on the bottom for two and half days before it was salvaged by the ''Limiting Factor'' (crew: Patrick Lahey, Pilot; Jonathan Struwe, [[DNV GL]] Specialist) from an estimated depth of {{convert|10927|m|ft|abbr=on}}.<ref>{{cite web|url=https://www.dnvgl.com/expert-story/maritime-impact/Dive-to-the-ultimate-abyss.html|title=Dive to the ultimate abyss|work=dnvgl.com|access-date=19 December 2019|archive-date=22 December 2019|archive-url=https://web.archive.org/web/20191222083907/https://www.dnvgl.com/expert-story/maritime-impact/Dive-to-the-ultimate-abyss.html|url-status=live}}</ref><ref name="ioc-unesco.org"/> The gathered data was published with the caveat that it was subject to further analysis and could possibly be revised in the future. The data will be donated to the GEBCO Seabed 2030 initiative.<ref>{{cite web |url=https://fivedeeps.com/wp-content/uploads/2019/05/FDE-Challenger-Release-FINAL-5132019.pdf |title=Deepest Submarine Dive in History, Five Deeps Expedition Conquers Challenger Deep |work=fivedeeps.com |access-date=13 May 2019 |archive-date=3 February 2020 |archive-url=https://web.archive.org/web/20200203210835/https://fivedeeps.com/wp-content/uploads/2019/05/FDE-Challenger-Release-FINAL-5132019.pdf |url-status=live}}</ref><ref name="BBC News"/><ref>{{cite web| url = https://seabed2030.gebco.net/| title = The Nippon Foundation-GEBCO Seabed 2030 Project| access-date = 19 June 2019| archive-date = 16 June 2019| archive-url = https://web.archive.org/web/20190616070107/https://seabed2030.gebco.net/}}</ref><ref>{{cite web|url=https://seabed2030.gebco.net/resources_for_journalists/press_release_2019-03-11.html|title=Major partnership announced between The Nippon Foundation-GEBCO Seabed 2030 Project and The Five Deeps Expedition|date=11 March 2019|website=gebco.net|access-date=19 June 2019|archive-date=19 June 2019|archive-url=https://web.archive.org/web/20190619174227/https://seabed2030.gebco.net/resources_for_journalists/press_release_2019-03-11.html}}</ref><ref>{{cite web |url=https://fivedeeps.com/home/technology/landers/ |title=Science Landers Flere, Skaff & Closp |work=fivedeeps.com |access-date=22 October 2019 |archive-date=19 July 2019 |archive-url=https://web.archive.org/web/20190719171454/https://fivedeeps.com/home/technology/landers/ |url-status=live}}</ref> Later in 2019, following a review of bathymetric data, and multiple sensor recordings taken by the DSV ''Limiting Factor'' and the ultra-deep-sea landers ''Closp'', ''Flere'' and ''Skaff'', the Five Deeps Expedition revised the maximum depth to {{Convert|10925|m|ft|abbr=on}} ±{{Convert|4|m|ft|abbr=on}}.<ref>{{cite web |url=https://fivedeeps.com/home/expedition/ |title=The Five Deeps Expedition Overview |work=fivedeeps.com |access-date=5 November 2019 |archive-date=10 June 2019 |archive-url=https://web.archive.org/web/20190610030231/https://fivedeeps.com/home/expedition/ |url-status=live}}</ref>

====2020 – ''Ring of Fire Expedition / DSV Limiting Factor''====
{{main|DSV Limiting Factor}}
[[File:Limiting Factor floating on the water surface.jpg|thumb|DSV ''Limiting Factor'' floating on the water surface]]

Caladan Oceanic's "Ring of Fire" expedition in the Pacific included six manned descents and twenty-five lander deployments into all three basins of the Challenger Deep all piloted by [[Victor Vescovo]] and further topographical and marine life survey of the entire Challenger Deep.<ref>{{cite web |url=https://caladanoceanic.com/expeditions/ringoffire/ |title=The Ring of Fire Expedition Overview |work=caladanoceanic.com |access-date=9 June 2020 |archive-date=8 June 2020 |archive-url=https://web.archive.org/web/20200608152244/https://caladanoceanic.com/expeditions/ringoffire/ |url-status=live}}</ref> The expedition craft used are the Deep Submersible Support Vessel DSSV ''Pressure Drop'', Deep-Submergence Vehicle DSV ''Limiting Factor'' and the ultra-deep-sea landers ''Closp'', ''Flere'' and ''Skaff''.
During the first manned dive on 7 June 2020 Victor Vescovo and former US astronaut (and former NOAA Administrator) [[Kathryn D. Sullivan]] descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor''.<ref>{{cite web |url=http://www.collectspace.com/news/news-060820a-astronaut-sullivan-challenger-deep.html |title=Former astronaut becomes first person to visit both space and the deepest place in the ocean |work=collectspace.com |access-date=9 June 2020 |archive-date=11 July 2020 |archive-url=https://web.archive.org/web/20200711022902/http://www.collectspace.com/news/news-060820a-astronaut-sullivan-challenger-deep.html |url-status=live}}</ref><ref>{{cite web |url=https://edition.cnn.com/travel/article/astronaut-kathy-sullivan-challenger-deep-dive-scn/index.html |title=Astronaut Kathy Sullivan is first woman to dive to Challenger Deep |work=cnn.com |date=10 June 2020 |access-date=10 June 2020 |archive-date=10 June 2020 |archive-url=https://web.archive.org/web/20200610145606/https://edition.cnn.com/travel/article/astronaut-kathy-sullivan-challenger-deep-dive-scn/index.html |url-status=live}}</ref>

On 12 June 2020, Victor Vescovo and mountaineer and explorer [[Vanessa O'Brien]] descended to the "Eastern Pool" of the Challenger Deep spending three hours mapping the bottom. O'Brien said her dive scanned about a mile of desolate bottom terrain, finding that the surface is not flat, as once was thought, but sloping by about {{convert|18|ft|m|1|abbr=on|lk=on}} per mile, subject to verification.<ref>{{cite web |url=https://metro.co.uk/2020/06/16/female-explorer-becomes-first-reach-highest-lowest-points-planet-reveals-what-was-like-journeying-4-hours-ocean-floor-12857647/ |title=Explorer becomes the first woman to reach the highest and lowest points on the planet |work=metro.co.uk |date=16 June 2020 |access-date=23 June 2020 |archive-date=16 June 2020 |archive-url=https://web.archive.org/web/20200616134000/https://metro.co.uk/2020/06/16/female-explorer-becomes-first-reach-highest-lowest-points-planet-reveals-what-was-like-journeying-4-hours-ocean-floor-12857647/ |url-status=live}}</ref><ref>{{cite web |url=https://jedennews.com/second-woman-to-make-challenger-deep-ocean-dive/ |title=Second Woman to Make Challenger Deep Ocean Dive |work=jedennews.com |access-date=13 June 2020 |archive-date=13 June 2020 |archive-url=https://web.archive.org/web/20200613100758/https://jedennews.com/second-woman-to-make-challenger-deep-ocean-dive/}}</ref><ref>{{cite web |url=https://www.forbes.com/sites/jimclash/2020/06/18/voyage-to-the-bottom-of-the-earth/ |title=Voyage to the Bottom of the Earth |work=forbes.com |access-date=21 June 2020 |archive-date=7 July 2020 |archive-url=https://web.archive.org/web/20200707063259/https://www.forbes.com/sites/jimclash/2020/06/18/voyage-to-the-bottom-of-the-earth/ |url-status=live}}</ref><ref>{{Cite web|title=To the Bottom of the Sea: Interview with Vanessa O'Brien|url=https://explorersweb.com/2020/06/23/to-the-bottom-of-the-sea-interview-with-vanessa-obrien/|access-date=2020-06-25|website=Explorersweb|date=23 June 2020 |archive-date=25 June 2020|archive-url=https://web.archive.org/web/20200625162246/https://explorersweb.com/2020/06/23/to-the-bottom-of-the-sea-interview-with-vanessa-obrien/|url-status=live}}</ref>
On 14 June 2020, Victor Vescovo and John Rost descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor'' spending four hours at depth and transiting the bottom for nearly 2 miles.<ref>{{cite tweet|number=1272342697551028230|user=VictorVescovo|title=Yesterday we just completed the deepest, longest dive ever. Mission specialist John Rost and I explored the Eastern…<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=21 June 2020|date=15 June 2020}}</ref>
On 20 June 2020, Victor Vescovo and Kelly Walsh descended to the "Western Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor'' spending four hours at the bottom. They reached a maximum depth of {{Convert|10923|m|ft|abbr=on}}. Kelly Walsh is the son of the ''[[Trieste (bathyscaphe)|Trieste's]]'' captain [[Don Walsh]] who descended there in 1960 with [[Jacques Piccard]].<ref>{{cite news |url=https://www.bbc.com/news/science-environment-53112621 |title=Mariana Trench: Don Walsh's son repeats historic ocean dive |work=bbc.com |date=20 June 2020 |access-date=21 June 2020 |archive-date=23 June 2020 |archive-url=https://web.archive.org/web/20200623122434/https://www.bbc.com/news/science-environment-53112621 |url-status=live}}</ref><ref>{{cite web|url=https://caladanoceanic.com/wp-content/uploads/2020/06/EYOS-Expeditions-Kelly-Walsh-dive-20th-June-2020.pdf |archive-url=https://web.archive.org/web/20201021022307/https://caladanoceanic.com/wp-content/uploads/2020/06/EYOS-Expeditions-Kelly-Walsh-dive-20th-June-2020.pdf |archive-date=2020-10-21 |url-status=live |title=From father to son; the next generation of ocean exploration. Kelly Walsh repeats father's historic dive, 60 years later, on Father's Day weekend |work=caladanoceanic.com |access-date=4 August 2020}}</ref>
On 21 June 2020, Victor Vescovo and Woods Hole Oceanographic Institution researcher Ying-Tsong Lin descended to the "Central Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor''. They reached a maximum depth of {{Convert|10915|m|ft|abbr=on}} ±{{Convert|4|m|ft|abbr=on}}.<ref>{{cite web |url=https://twitter.com/CaladanOceanic |title=On our latest dive, @WHOI research scientist Dr. Ying-Tsong "Y.-T". Lin joined @VictorVescovo to become, not only the first person born in Taiwan to go to the bottom of the Mariana Trench, but also the first from the Asian continent to do so.work=@CaladanOceanic twitter.com |access-date=24 June 2020 |archive-date=24 June 2020 |archive-url=https://web.archive.org/web/20200624123831/https://twitter.com/caladanoceanic |url-status=live}}</ref><ref>{{cite web |url=https://www.whoi.edu/press-room/news-release/whoi-researcher-dives-to-challenger-deep/ |title=WHOI Researcher Dives to Challenger Deep |work=whoi.edu |access-date=27 June 2020 |archive-date=29 June 2020 |archive-url=https://web.archive.org/web/20200629024615/https://www.whoi.edu/press-room/news-release/whoi-researcher-dives-to-challenger-deep/ |url-status=live}}</ref><ref>{{cite web|url=https://caladanoceanic.com/wp-content/uploads/2020/06/PhaseV_YTRelease_FINAL.pdf |archive-url=https://web.archive.org/web/20201021023506/https://caladanoceanic.com/wp-content/uploads/2020/06/PhaseV_YTRelease_FINAL.pdf |archive-date=2020-10-21 |url-status=live |title=First Taiwanese Native Dives to Challenger Deep |work=caladanoceanic.com |access-date=4 August 2020}}</ref>
On 26 June 2020 Victor Vescovo and Jim Wigginton descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle ''Limiting Factor''.<ref>{{cite web |url=https://tritonsubs.com/2020/07/01/8773/ |title=Caladan Oceanic Revisits Challenger Deep in Month-Long Dive Series |work=tritonsubs.com |access-date=29 July 2020 |archive-date=29 July 2020 |archive-url=https://web.archive.org/web/20200729135248/https://tritonsubs.com/2020/07/01/8773/}}</ref>

====2020 – ''Fendouzhe''====
{{main|Striver (bathyscaphe)}}

[[File:The chinese submersible Fendouzhe aboard its mother ship Tan Suo Yi Hao.jpg|thumb|upright|''Fendouzhe'' aboard its mother ship ''Tansuo Yi Hao'']]

''Fendouzhe'' (奋斗者, ''Striver'') is a manned [[China|Chinese]] deep-sea submersible developed by the China Ship Scientific Research Center (CSSRC). Between 10 October and 28 November, 2020, it carried out thirteen dives in the Mariana Trench as part of a test programme. Of these, eight led to depths of more than {{convert|10000|m|ft|0|abbr=on}}. On 10 November 2020, the bottom of the Challenger Deep was reached by ''Fendouzhe'' with three Chinese scientists (Zhāng Wěi 张伟 [pilot], Zhào Yáng 赵洋, and Wáng Zhìqiáng 王治强) onboard whilst live-streaming the descent to a reported depth of {{convert|10909|m|ft|0|abbr=on}}.<ref name="Fendouze3">{{Cite web|title=Chinese submarine reaches the deepest place on Earth|url=https://www.livescience.com/chinese-submarine-record-dive.html|access-date=2021-04-26|website=interestingengineering.com|date=30 November 2020 |language=en-US|archive-date=26 April 2021|archive-url=https://web.archive.org/web/20210426104528/https://www.livescience.com/chinese-submarine-record-dive.html|url-status=live}}</ref><ref name="Fendouze1">{{Cite web|title=Chinese Submersible "Fendouzhe" Descended to Earth's Deepest Oceanic Trench|url=https://www.sciencetimes.com/articles/28350/20201121/chinese-submersible-fendouzhe-descended-earths-deepest-oceanic-trench.htm|access-date=2021-04-26|website=sciencetimes.com|date=21 November 2020 |language=en-US|archive-date=16 September 2021|archive-url=https://web.archive.org/web/20210916190150/https://www.sciencetimes.com/articles/28350/20201121/chinese-submersible-fendouzhe-descended-earths-deepest-oceanic-trench.htm|url-status=live}}</ref> This makes the '' Fendouzhe '' the fourth manned submersible vehicle achieving a successful descent. The pressure hull of ''Fendouzhe'', made from a newly developed titanium alloy, offers space for three people in addition to technical equipment.<ref name="Fendouze2">{{Cite web|title=Chinese Manned Submersible Reaches Deepest Part of Mariana Trench|url=https://interestingengineering.com/chinese-manned-submersible-reaches-deepest-part-of-mariana-trench|access-date=2021-04-26|website=interestingengineering.com|date=26 November 2020 |language=en-US|archive-date=26 April 2021|archive-url=https://web.archive.org/web/20210426104525/https://interestingengineering.com/chinese-manned-submersible-reaches-deepest-part-of-mariana-trench|url-status=live}}</ref> ''Fendouzhe'' is equipped with cameras made by the Norwegian manufacturer Imenco.<ref name="Fendouze8">{{Cite web|title=Imenco in the worlds deepest waters|url=https://imenco.no/imenco-in-the-worlds-deepest-waters|access-date=2021-04-28|website=imenco.no|date=23 November 2020 |language=en-US|archive-date=28 April 2021|archive-url=https://web.archive.org/web/20210428100327/https://imenco.no/imenco-in-the-worlds-deepest-waters|url-status=live}}</ref>
According to Ye Cong 叶聪, the chief designer of the submersible, China's goals for the dive aren't just scientific investigation but also the future use of deep-sea seabed resources.<ref name="Fendouze6">{{Cite web|title=China breaks national record for Mariana Trench manned-dive amid race for deep sea resources|url=https://edition.cnn.com/2020/11/11/asia/china-record-dive-mariana-trench-intl-hnk/index.html|access-date=2021-04-26|website=cnn.com|date=11 November 2020 |language=en-US|archive-date=12 April 2021|archive-url=https://web.archive.org/web/20210412034036/https://edition.cnn.com/2020/11/11/asia/china-record-dive-mariana-trench-intl-hnk/index.html|url-status=live}}</ref><ref name="Fendouze7">{{Cite news|title=Chinese submarine sends first live video back from the bottom of the Mariana Trench|url=https://www.abc.net.au/news/2020-11-29/chinese-sub-reaches-deepest-ocean-trench-mariana-fendouzhe/12932462|access-date=2021-04-27|newspaper=ABC News|date=29 November 2020 |language=en-US|archive-date=24 July 2021|archive-url=https://web.archive.org/web/20210724015107/https://www.abc.net.au/news/2020-11-29/chinese-sub-reaches-deepest-ocean-trench-mariana-fendouzhe/12932462|url-status=live}}</ref>

====2021 – ''Ring of Fire 2 Expedition / DSV Limiting Factor''====
{{main|DSV Limiting Factor}}
On 28 February 2021 Caladan Oceanic's "Ring of Fire 2" expedition arrived over the Challenger Deep and conducted manned descents and lander deployments into the Challenger Deep.<ref>{{cite web| url = https://twitter.com/VictorVescovo| title = Victor Vescovo @ twitter| access-date = 21 June 2020| archive-date = 20 March 2021| archive-url = https://web.archive.org/web/20210320061916/https://twitter.com/VictorVescovo| url-status = live}}</ref> At the start the (uncrewed) ultra-deep-sea lander ''Skaff'' was deployed to collect water column data by CTD for the expedition. The effects of the Pacific subducting plate crashing into the Philippine Plate was among the things researched onsite.
On 1 March 2021, the first manned descent to the eastern pool was made by Victor Vescovo and [[Richard Garriott]].<ref>{{cite web| url = https://twitter.com/RichardGarriott/status/1366326951372328962| title = Richard Garriott @ twitter| access-date = 2 March 2021| archive-date = 1 March 2021| archive-url = https://web.archive.org/web/20210301095935/https://twitter.com/RichardGarriott/status/1366326951372328962| url-status = live}}</ref> Garriott became the 17th person to descend to the bottom.<ref>{{cite web |url=https://www.mirror.co.uk/news/uk-news/history-making-brit-explorer-dives-23593598 |title=Brit spaceman's incredible pictures from the bottom the Earth – including selfie |work=mirror.co.uk |date=2 March 2021 |access-date=3 March 2021 |archive-date=2 March 2021 |archive-url=https://web.archive.org/web/20210302195003/https://www.mirror.co.uk/news/uk-news/history-making-brit-explorer-dives-23593598 |url-status=live}}</ref><ref name="collectspace.com">{{cite web |url=http://www.collectspace.com/news/news-030321a-astronaut-garriott-dive-challenger-deep.html |title=Astronaut-explorer sets records on dive to deepest point on Earth |work=collectspace.com |access-date=6 March 2021 |archive-date=5 March 2021 |archive-url=https://web.archive.org/web/20210305083455/http://www.collectspace.com/news/news-030321a-astronaut-garriott-dive-challenger-deep.html |url-status=live}}</ref>
On 2 March 2021, a descent to the eastern pool was made by Victor Vescovo and [[Michael Dubno]].<ref name="collectspace.com"/><ref>{{cite web| url = https://twitter.com/hashtag/venturetothedeep?src=hashtag_click| title = VentureToTheDeep @ twitter| access-date = 15 March 2021| archive-date = 24 December 2021| archive-url = https://web.archive.org/web/20211224185749/https://twitter.com/hashtag/venturetothedeep?src=hashtag_click| url-status = live}}</ref>
On 5 March a descent to the eastern pool was made by Victor Vescovo and [[Hamish Harding]].<ref>{{cite web |url=https://www.gulftoday.ae/news/2021/03/05/dubai-resident-hamish-harding-explores-ocean-deepest-point-challenger-deep |title=Dubai resident Hamish Harding explores ocean's deepest point 'Challenger Deep' in record-breaking attempt |work=gulftoday.ae |access-date=6 March 2021 |format=video |archive-date=5 March 2021 |archive-url=https://web.archive.org/web/20210305210749/https://www.gulftoday.ae/news/2021/03/05/dubai-resident-hamish-harding-explores-ocean-deepest-point-challenger-deep |url-status=live}}</ref> They traversed the bottom of Challenger Deep.<ref>{{cite web| url = https://www.facebook.com/ActionAviationChairman/| title = Hamish Harding @ facebook| website = [[Facebook]]}}</ref><ref>{{cite web| url = https://twitter.com/actionaviation0| title = Hamish Harding @ twitter| access-date = 6 March 2021| archive-date = 20 March 2021| archive-url = https://web.archive.org/web/20210320062151/https://twitter.com/ActionAviation0| url-status = live}}</ref>
On 11 March 2021 a descent to the Western Pool was made by Victor Vescovo and marine botanist [[Nicole Yamase]].<ref>{{cite web| url = https://www.facebook.com/BlueProsperityMicronesia/posts/257836152625175 |archive-url=https://ghostarchive.org/iarchive/facebook/113462413729217/257836152625175 |archive-date=2022-02-25 |url-access=limited| title = Blue Prosperity Micronesia @ Facebook|website=[[Facebook]]}}{{cbignore}}</ref>
On 13 April 2021 a descent was made by deep water submersible operations expert [[Rob McCallum]] and Tim Macdonald who piloted the dive.<ref>{{cite web |url=https://www.stuff.co.nz/science/124823189/historymaking-109km-anzac-dive-to-the-bottom-of-the-mariana-trench |title=History-making 10.9km 'Anzac Dive' to the bottom of the Mariana Trench |work=stuff.co.nz |date=13 April 2021 |access-date=17 April 2021 |archive-date=16 April 2021 |archive-url=https://web.archive.org/web/20210416222540/https://www.stuff.co.nz/science/124823189/historymaking-109km-anzac-dive-to-the-bottom-of-the-mariana-trench |url-status=live}}</ref><ref name="ANZAC Dive">{{Cite web|title='The ANZAC Dive': Australian, New Zealander Dive To Challenger Deep – DeeperBlue.com|url=https://www.deeperblue.com/the-anzac-dive-australian-new-zealander-dive-to-challenger-deep/|access-date=2021-04-10|website=www.deeperblue.com|language=en-US|archive-date=10 April 2021|archive-url=https://web.archive.org/web/20210410024556/https://www.deeperblue.com/the-anzac-dive-australian-new-zealander-dive-to-challenger-deep/|url-status=live}}</ref><ref name="challengeranzac">{{Cite web|title=Challenger Deep ANZAC Expedition|url=https://caladanoceanic.com/expeditions/challengeranzac/|access-date=2021-04-18|website=caladanoceanic.com|language=en-US|archive-date=18 April 2021|archive-url=https://web.archive.org/web/20210418130115/https://caladanoceanic.com/expeditions/challengeranzac/|url-status=live}}</ref>
A 2021 descent with a Japanese citizen is planned.<ref name="challengerjapan">{{Cite web|title=Challenger Deep Japanese Expedition|url=https://caladanoceanic.com/expeditions/challengerjapan/|access-date=2021-04-18|website=caladanoceanic.com|language=en-US|archive-date=18 April 2021|archive-url=https://web.archive.org/web/20210418130117/https://caladanoceanic.com/expeditions/challengerjapan/}}</ref>
All manned descents were conducted in the Deep-Submergence Vehicle ''[[Triton Submarines|DSV Limiting Factor]]''.

====2022 - ''Ring of Fire 3 Expedition / DSV Limiting Factor''====
{{main|DSV Limiting Factor}}
{{multiple image
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 | image1    = Dr Dawn Wright and CDR Victor Vescovo Challenger Deep Dive 071222 Western Pool-1.jpg
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 | caption1  = <small>Dawn Wright and Victor Vescovo aboard DSV ''Limiting Factor'' during their July 2022 dive into the Western Pool</small>
 | image2    = Challenger Deep Dive 071222 by V Vescovo in DSV Limiting Factor - Southern Wall of Western Pool.jpg
 | alt2      =
 | caption2  = <small>Southern wall of the Western Pool</small>
}}

In July 2022 for the fourth consecutive year, Caladan Oceanic's deep submergence system, consisting of the deep submersible DSV ''Limiting Factor'' supported by the mother ship DSSV ''Pressure Drop'', returned to the Challenger Deep for dives into the Challenger Deep.<ref>[https://www.facebook.com/pg/Dssvpressuredrop/posts/ @Dssvpressuredrop on Twitter]</ref>
In early July 2022, Victor Vescovo was joined by Aaron Newman as a mission specialist for a dive into the Central pool.<ref>{{cite tweet|number=1544086485556658179|user=VictorVescovo|title=Completed a dive into the Challenger Deep, Central Pool with Aaron Newman...<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=22 July 2022|date=5 July 2022}}</ref> On 5 July 2022, Tim Macdonald as pilot and Jim Kitchen as mission specialist for a dive into the Eastern pool.<ref>{{cite tweet|number=1545243188692193281|user=VictorVescovo|title=A dive at Challenger Deep (CD) was completed on July 5th with Tim Macdonald as pilot and Jim Kitchen as mission specialist...<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=22 July 2022|date=8 July 2022}}</ref> On 8 July 2022 Victor Vescovo was joined by [[Dylan Taylor (executive)|Dylan Taylor]] as mission specialist for a dive into the Eastern pool.<ref>{{cite tweet|number=1545244724612694017|user=VictorVescovo|title=Completed another dive into the western, unvisited, area of the Eastern Pool of CD with Dylan Taylor...<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=22 July 2022|date=8 July 2022}}</ref>
Victor Vescovo (for his 15th dive into the Challenger Deep) was joined by geographer and oceanographer [[Dawn Wright]] as mission specialist on the 12 July 2022 dive to {{convert|10919|m|ft|0|abbr=on}} in the Western Pool.<ref>{{Cite web |url=https://divernet.com/world-dives/deep-sea-mapper-cant-get-much-deeper/ |title=Deep-sea mapper can't get much deeper! divernet.com 15 July 2022 |date=15 July 2022 |access-date=16 July 2022 |archive-date=15 July 2022 |archive-url=https://web.archive.org/web/20220715101107/https://divernet.com/world-dives/deep-sea-mapper-cant-get-much-deeper/ |url-status=live}}</ref><ref>{{cite tweet|number=1547122307646341122|user=VictorVescovo|title=Dr. Dawn Wright and I completed a dive to 10,919m +/- 6m at the bottom of Challenger Deep (my 15th visit), Western Pool.<!-- full text of tweet that Twitter returned to the bot (excluding links) added by TweetCiteBot. This may be better truncated or may need expanding (TW limits responses to 140 characters) or case changes. --> |accessdate=22 July 2022|date=13 July 2022}}</ref> Wright operated the world's first sidescan sonar to ever operate at full-ocean depth to capture detailed imagery along short transects of the southern wall of the Western Pool.<ref>{{cite web |last1=EYOS Expeditions Blog |title=Dawn Wright Successfully Dives Challenger Deep |url=https://www.eyos-expeditions.com/dawn-wright-successfully-dives-challenger-deep/ |website=EYOS Expeditions |date=13 July 2022 |access-date=28 July 2022 |archive-date=14 July 2022 |archive-url=https://web.archive.org/web/20220714010910/https://www.eyos-expeditions.com/dawn-wright-successfully-dives-challenger-deep/ |url-status=live}}</ref><ref>{{cite web |last1=Deep Ocean Search |title=DOS to integrate the world's first 'Full Ocean Depth' side scan sonar |url=http://www.deepoceansearch.com/2021/12/01/dos-to-integrate-the-first-full-ocean-depth-side-scan-sonar-for-caladan-oceanic/ |website=Deep Ocean Search News |date=December 2021 |publisher=Deep Ocean Search |access-date=28 July 2022 |archive-date=18 August 2022 |archive-url=https://web.archive.org/web/20220818041209/http://www.deepoceansearch.com/2021/12/01/dos-to-integrate-the-first-full-ocean-depth-side-scan-sonar-for-caladan-oceanic/ |url-status=live}}</ref>

===Uncrewed descents by ROVs===
====1996 and 1998 – ''Kaikō''====
{{Main|Kaikō ROV}}

The remotely operated vehicle (ROV) ''Kaikō'' made many uncrewed descents to the Mariana Trench from its support ship RV ''Yokosuka'' during two expeditions in 1996 and 1998.<ref>{{cite web|url=https://www.mbari.org/wp-content/uploads/2016/01/Barry-and-Hashimoto-Challenger-deep-2009.pdf |archive-url=https://web.archive.org/web/20161220205139/https://www.mbari.org/wp-content/uploads/2016/01/Barry-and-Hashimoto-Challenger-deep-2009.pdf |archive-date=2016-12-20 |url-status=live |title=Revisiting the Challenger Deep using the ROV Kaiko |publisher=Winter 2009 Volume 43, Number 5 |access-date=15 December 2016}}</ref>
From 29 February to 4 March the ROV ''Kaiko'' made three dives into the ''central'' basin, ''Kaiko'' #21 – ''Kaiko'' #23, . Depths ranged from {{convert|10898|m|ft}} at {{Coord|11|22.536|N|142|26.418|E}}, to {{convert|10896|m|ft}} at {{Coord|11|22.59|N|142|25.848|E}}; dives #22 & #23 to the north, and dive #21 northeast of the deepest waters of the ''central'' basin.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/dive/kaiko/21/e| title = Partial suspension of access to the data and services on our website < About JAMSTEC < JAMSTEC| access-date = 17 November 2019| archive-date = 17 November 2019| archive-url = https://web.archive.org/web/20191117232748/http://www.godac.jamstec.go.jp/darwin/dive/kaiko/21/e| url-status = live}}</ref> During the 1996 measurements the temperature (water temperature increases at great depth due to adiabatic compression), [[salinity]] and water pressure at the sampling station was {{convert|2.6|°C|°F}}, 34.7‰ and {{convert|1113|bar|MPa psi|abbr=on}}, respectively at {{convert|10897|m|0|abbr=on}} depth.<ref name="Akimoto">{{Cite journal| author=Akimoto | title=The deepest living foraminifera, Challenger Deep, Mariana Trench | journal=Marine Micropaleontology | volume=42 | issue=1–2 | year=2001 | page=95 | doi=10.1016/S0377-8398(01)00012-3|display-authors=etal| bibcode=2001MarMP..42...95A}}</ref> The Japanese robotic deep-sea probe ''Kaikō'' broke the depth record for uncrewed probes when it reached close to the surveyed bottom of the Challenger Deep. Created by the [[Japan Agency for Marine-Earth Science and Technology|Japan Agency for Marine-Earth Science and Technology (JAMSTEC)]], it was one of the few uncrewed deep-sea probes in operation that could dive deeper than {{convert|6000|m}}. The manometer measured depth of {{convert|10911.4|m|0|abbr=on}} ±{{convert|3|m|ft|0|abbr=on}} at {{Coord|11|22.39|N|142|35.54|E}} for the Challenger Deep is believed to be the most accurate measurement taken up to then.<ref>{{cite web |url=http://www.jamstec.go.jp/e/about/equipment/ships/kaiko7000.html |title=Kaiko 7000II |publisher=Japan Agency for Marine-Earth Science and Technology – note: this ref. contains a date error |access-date=26 March 2012 |archive-date=10 April 2020 |archive-url=https://web.archive.org/web/20200410211118/http://www.jamstec.go.jp/e/about/equipment/ships/kaiko7000.html |url-status=live}}</ref><ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/>
Another source states the greatest depth measured by ''Kaikō'' in 1996 was {{convert|10898|m|0|abbr=on}} at {{Coord|11|22.10|N|142|25.85|E}} and {{convert|10907|m|0|abbr=on}} at {{Coord|11|22.95|N|142|12.42|E}} in 1998.<ref name="Bathymetric mapping of the world's deepest seafloor, Challenger Deep"/>
The ROV ''Kaiko'' was the first vehicle to visit to the bottom of the Challenger Deep since the bathyscaph ''Trieste'''s dive in 1960, and the first success in sampling the trench bottom sediment/mud, from which ''Kaiko'' obtained over 360 samples.<ref>Nakanishi, M., "A Precise Bathymetric map of the World's deepest seafloor, Challenger Deep in the Mariana Trench," Marine Geophysical Research, Table 2, 2011, page 1</ref> Approximately 3,000 different microbes were identified in the samples.<ref>Cruise Summary, YK09-08, Taishi Tsubouchi "Challenger Area" page 11</ref><ref name="ngnews">[http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html "Life Is Found Thriving at Ocean's Deepest Point"] {{Webarchive|url=https://web.archive.org/web/20120822121902/http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html |date=22 August 2012}}, National Geographic News, 3 February 2005</ref><ref name="Akimoto"/>
''Kaikō'' was lost at sea off [[Shikoku|Shikoku Island]] during [[2003 Pacific typhoon season#Typhoon Chan-hom|Typhoon Chan-Hom]] on 29 May 2003.

====2009 – ''Nereus''====
[[File:Nereus (underwater vehicle) hydro20100720-full.jpg|thumb|HROV Nereus]]

{{Main|Nereus (underwater vehicle)}}
From 2 May to 5 June 2009, the RV ''Kilo Moana'' hosted the [[Woods Hole Oceanographic Institution]] ([[Woods Hole Oceanographic Institution|WHOI]]) hybrid remotely operated vehicle (HROV) ''[[Nereus (underwater vehicle)|Nereus]]'' team for the first operational test of the ''{{ship||Nereus|underwater vehicle|2}}'' in its 3-ton tethered ROV mode. The ''Nereus'' team was headed by the Expedition Leader Andy Bowen of WHOI, Louis Whitcomb of [[Johns Hopkins University]], and Dana Yoerger, also of WHOI. The expedition had co-chief scientists: biologist Tim Shank of WHOI, and geologist Patricia Fryer of the University of Hawaiʻi, to head the science team exploiting the ship's [[bathymetry]] and organizing the science experiments deployed by the ''Nereus''.<ref>{{cite web| url = https://www.whoi.edu/press-room/news-release/hybrid-remotely-operated-vehicle-nereus-reaches-deepest-part-of-the-ocean/| title = Hybrid Remotely Operated Vehicle Nereus Reaches Deepest Part of the Ocean| access-date = 28 November 2019| archive-date = 12 April 2019| archive-url = https://web.archive.org/web/20190412164352/https://www.whoi.edu/press-room/news-release/hybrid-remotely-operated-vehicle-nereus-reaches-deepest-part-of-the-ocean/| url-status = live}}</ref> From ''Nereus'' dive #007ROV to {{convert|880|m|0|abbr=on}} just south of Guam, to dive #010ROV into the [[Mariana Trench|Nero Deep]] at {{convert|9050|m|0|abbr=on}}, the testing gradually increased depths and complexities of activities at the bottom.

Dive #011ROV, on 31 May 2009, saw the ''Nereus'' piloted on a 27.8-hour underwater mission, with about ten hours transversing the ''eastern'' basin of the Challenger Deep – from the south wall, northwest to the north wall – streaming live video and data back to its mothership. A maximum depth of {{convert|10902|m|0|abbr=on}} was registered at {{Coord|11|22.10|N|142|35.48|E}}. The ''{{ship|RV|Kilo Moana}}'' then relocated to the ''western'' basin, where a 19.3-hour underwater dive found a maximum depth of {{convert|10899|m|0|abbr=on}} on dive #012ROV, and on dive #014ROV in the same area (11°19.59 N, 142°12.99 E) encountered a maximum depth of {{convert|10176|m|0|abbr=on}}. The ''Nereus'' was successful in recovering both sediment and rock samples from the ''eastern'' and the ''western'' basins with its manipulator arm for further scientific analysis. The HROV's final dive was about {{convert|80|nmi|km|1|abbr=on}} to the north of the Challenger Deep, in the [[backarc]], where they dived {{convert|2963|m|0|abbr=on}} at the TOTO Caldera (12°42.00 N, 143°31.5 E).<ref name="unols.org">{{cite web| url = https://www.unols.org/sites/default/files/200912desap15.pdf| title = Operations of the Nereus Underwater Robotic Vehicle, DESSC, 13 December 2009| access-date = 28 November 2019| archive-date = 28 November 2019| archive-url = https://web.archive.org/web/20191128055501/https://www.unols.org/sites/default/files/200912desap15.pdf| url-status = live}}</ref><ref name="Robot sub reaches deepest ocean">{{cite news|url=https://news.bbc.co.uk/2/hi/science/nature/8080324.stm|title=Robot sub reaches deepest ocean|date=3 June 2009|access-date=3 June 2009|work=BBC News|archive-date=30 October 2019|archive-url=https://web.archive.org/web/20191030165503/http://news.bbc.co.uk/2/hi/science/nature/8080324.stm|url-status=live}}</ref> Nereus thus became the first vehicle to reach the Mariana Trench since 1998 and the deepest-diving vehicle then in operation.<ref name="Robot sub reaches deepest ocean"/> Project manager and developer Andy Bowen heralded the achievement as "the start of a new era in ocean exploration".<ref name="Robot sub reaches deepest ocean"/> ''Nereus'', unlike ''Kaikō'', did not need to be powered or controlled by a cable connected to a ship on the ocean surface.<ref name="Nereus">{{cite web|url=http://www.physorg.com/news163167519.html|title='Nereus' reaches deepest part of the ocean|date=2 June 2009|access-date=2 June 2009|publisher=physorg.com|archive-date=6 June 2011|archive-url=https://web.archive.org/web/20110606085530/http://www.physorg.com/news163167519.html|url-status=live}}</ref><ref name="Daily Reports for R/V KILO MOANA" /><ref name="Robot sub reaches deepest ocean"/><ref name="Daily Reports for R/V KILO MOANA April and May 2009">{{Cite news|url=http://www.soest.hawaii.edu/UMC/cms/ship-daily-reports/|title=Daily Reports for R/V KILO MOANA April and May 2009|date=31 May 2009|publisher=University of Hawaiʻi Marine Center|access-date=31 May 2009|archive-date=31 December 2013|archive-url=https://web.archive.org/web/20131231001444/http://www.soest.hawaii.edu/UMC/cms/ship-daily-reports/}}</ref><ref name="Nereus Mission">{{Cite news|url=http://www.whoi.edu/page.do?pid=7545&tid=282&cid=57586&ct=162|title=Hybrid Remotely Operated Vehicle "Nereus" Reaches Deepest Part of the Ocean|date=2 June 2009|publisher=Woods Hole Oceanographic Institution|access-date=2 June 2009|archive-date=13 July 2009|archive-url=https://web.archive.org/web/20090713052319/http://www.whoi.edu/page.do?pid=7545&tid=282&cid=57586&ct=162|url-status=live}}</ref><ref name="unols.org"/>
The HROV ''Nereus'' was lost on 10 May 2014 while conducting a dive at {{convert|9900|m|ft}} in depth in the [[Kermadec Trench]].<ref>{{cite news|url=https://www.bbc.com/news/science-environment-27374326|title=Deep-sea sub 'implodes' 10&nbsp;km-down|first=Jonathan|last=Amos|work=BBC News|date=12 May 2014|access-date=21 July 2018|archive-date=7 July 2018|archive-url=https://web.archive.org/web/20180707183011/https://www.bbc.com/news/science-environment-27374326|url-status=live}}</ref>

===Uncrewed descents near the Challenger Deep===
====2008 – ''ABISMO''====
{{Main|ABISMO}}

In June 2008, the [[Japan Agency for Marine-Earth Science and Technology]] (JAMSTEC) deployed the research vessel ''Kairei'' to the area of [[Guam]] for cruise KR08-05 Leg 1 and Leg 2.
On 1–3 June 2008, during Leg 1, the Japanese robotic deep-sea probe ''[[ABISMO]]'' (Automatic Bottom Inspection and Sampling Mobile) on dives 11–13 almost reached the bottom about {{convert|150|km|mi|0|abbr=on}} east of the Challenger Deep: "Unfortunately, we were unable to dive to the sea floor because the legacy primary cable of the Kaiko system was a little bit short. The 2-m long gravity core sampler was dropped in free fall, and sediment samples of 1.6m length were obtained. Twelve bottles of water samples were also obtained at various depths..." ABISMO's dive #14 was into the TOTO caldera (12°42.7777 N, 143°32.4055 E), about 60 nmi northeast of the deepest waters of the ''central'' basin of the Challenger Deep, where they obtained videos of the hydrothermal plume.<ref>{{cite web| url = https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf| title = Yoshida, H. et.al., The ABISMO Mud and Water Sampling ROV for Surveys at 11,000 m Depth, Marine Technology Society Journal, Winter 2009, Volume 43, Number 5, pages 87–96.| access-date = 15 December 2019| archive-date = 5 May 2019| archive-url = https://web.archive.org/web/20190505025229/https://www.globaloceandesign.com/uploads/3/0/7/4/30747513/2009_into_the_trench_part_1.pdf| url-status = live}}</ref> Upon successful testing to {{convert|10000|m|0|abbr=on}}, JAMSTEC' ROV ''ABISMO'' became, briefly, the only full-ocean-depth rated ROV in existence. On 31 May 2009, the ABISMO was joined by the Woods Hole Oceanographic Institution's HROV ''Nereus'' as the only two operational full ocean depth capable [[remotely operated vehicle]]s in existence. During the ROV ''ABISMO's'' deepest sea trails dive its [[manometer]] measured a depth of {{convert|10257|m|0|abbr=on}} ±{{convert|3|m|0|abbr=on}} in "Area 1" (vicinity of 12°43' N, 143°33' E).<ref>{{cite web| url = http://www.godac.jamstec.go.jp/catalog/data/doc_catalog/media/KR08-05_leg1-2_all.pdf| title = KAIREI Cruise Report KR08-05 Leg1: Sea Trials of the Deep Ocean ROV ABISMO 2008/05/26 – 2008/06/06 Leg2: 11,000 m class Free Fall Mooring System 2008/06/07 – 2008/06/14| access-date = 3 December 2019| archive-date = 3 December 2019| archive-url = https://web.archive.org/web/20191203065524/http://www.godac.jamstec.go.jp/catalog/data/doc_catalog/media/KR08-05_leg1-2_all.pdf| url-status = live}}</ref><ref>{{cite web| url = http://www.jamstec.go.jp/e/about/press_release/20080616/| title = "ABISMO", Automatic Bottom Inspection and Sampling Mobile, Succeeds in World's First Multiple Vertical Sampling from Mid-ocean, Sea Floor and Sub-seafloor over Depth of 10,000 m in Mariana Trench 16 June 2008 Japan Agency for Marine-Earth Science and Technology| access-date = 4 June 2015| archive-date = 19 January 2015| archive-url = https://web.archive.org/web/20150119201616/http://www.jamstec.go.jp/e/about/press_release/20080616/| url-status = live}}</ref>

Leg 2, under chief scientist Takashi Murashima, operated at the Challenger Deep 8–9 June 2008, testing JAMSTEC's new full ocean depth "Free Fall Mooring System," i.e. a [[Benthic lander|lander]]. The lander was successfully tested twice to {{convert|10895|m|0|abbr=on}} depth, taking video images and sediment samplings at {{Coord|11|22.14|N|142|25.76|E}}, in the ''central'' basin of the Challenger Deep.<ref>{{cite web| url = http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr08-05_leg2/e| title = KAIREI KR08-05 Leg2 Cruise Data| access-date = 3 December 2019| archive-date = 3 December 2019| archive-url = https://web.archive.org/web/20191203065448/http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr08-05_leg2/e| url-status = live}}</ref>

====2016 – ''Haidou-1''====
On 23 May 2016, the Chinese submersible ''Haidou-1'' dived to a depth of {{convert|10767|m|0|abbr=on}} at an undisclosed position in the Mariana Trench, making China the third country after Japan [[Kaikō ROV|(ROV ''Kaikō'']]), and the US [[Nereus (underwater vehicle)|(HROV ''Nereus'')]], to deploy a full-ocean-depth ROV. This autonomous and remotely operated vehicle has a design depth of {{convert|11000|m|0|abbr=on}}.<ref>{{cite web|url=https://www.chinadailyasia.com/nation/2016-08/23/content_15483551.html|title=Nitrogen experiment among breakthroughs|last=Xinying|first=Zhao|date=23 August 2016|website=[[China Daily]]|url-status=live|archive-url=https://web.archive.org/web/20181013133010/https://www.chinadailyasia.com/nation/2016-08/23/content_15483551.html|archive-date=13 October 2018}}</ref>

====2020 – ''Vityaz-D''====
On 8 May 2020, the Russian submersible ''Vityaz-D'' dived to a depth of {{convert|10028|m|0|abbr=on}} at an undisclosed position in the Mariana Trench.<ref>[https://www.rgo.ru/en/article/russian-submarine-vityaz-reached-bottom-mariana-trench RUSSIAN SUBMARINE "VITYAZ" REACHED THE BOTTOM OF THE MARIANA TRENCH] {{Webarchive|url=https://web.archive.org/web/20200609145725/https://www.rgo.ru/en/article/russian-submarine-vityaz-reached-bottom-mariana-trench |date=9 June 2020}}, Russian geographical society, 13 May 2020</ref>

==Lifeforms==
The summary report of the {{HMS|Challenger|1858|6}} expedition lists unicellular life forms from the two dredged samples taken when the Challenger Deep was first discovered.<ref>[http://www.19thcenturyscience.org/HMSC/HMSC-Reports/1895-Summary/htm/doc878.html] {{Webarchive|url=https://web.archive.org/web/20110310200116/http://www.19thcenturyscience.org/HMSC/HMSC-Reports/1895-Summary/htm/doc878.html|date=10 March 2011}}, entry on 23 March 1875.</ref> These (''[[Nassellaria]]'' and ''[[Spumellaria]]'') were reported in the Report on Radiolaria (1887)<ref>[http://www.19thcenturyscience.org/HMSC/HMSC-Reports/Zool-40/README.htm] {{Webarchive|url=https://web.archive.org/web/20100729070107/http://www.19thcenturyscience.org/HMSC/HMSC-Reports/Zool-40/README.htm|date=29 July 2010}}, Report on the Radiolaria collected by H.M.S. Challenger
by Ernst Haeckel.</ref> written by [[Ernst Haeckel]].

On their 1960 descent, the crew of the ''Trieste'' noted that the floor consisted of [[diatom]]aceous ooze and reported observing "some type of flatfish" lying on the seabed.<ref>[http://www.americanheritage.com/articles/magazine/it/1992/1/1992_1_28.shtml "To the bottom of the sea"] {{webarchive|url=https://web.archive.org/web/20081203173230/http://www.americanheritage.com/articles/magazine/it/1992/1/1992_1_28.shtml |date=3 December 2008}}, T. A. Heppenheimer, AmericanHeritage.com</ref>

{{blockquote |And as we were settling this final fathom, I saw a wonderful thing. Lying on the bottom just beneath us was some type of [[flatfish]], resembling a [[sole (fish)|sole]], about {{convert|1|ft|cm|disp=sqbr||}} long and {{convert|6|in|cm|disp=sqbr||}} across. Even as I saw him, his two round eyes on top of his head spied us{{spnd}}a monster of steel{{spnd}}invading his silent realm. Eyes? Why should he have eyes? Merely to see phosphorescence? The floodlight that bathed him was the first real light ever to enter this hadal realm. Here, in an instant, was the answer that biologists had asked for the decades. Could life exist in the greatest depths of the ocean? It could! And not only that, here apparently, was a true, bony [[teleost]] fish, not a primitive ray or [[elasmobranch]]. Yes, a highly evolved vertebrate, in time's arrow very close to man himself. Slowly, extremely slowly, this flatfish swam away. Moving along the bottom, partly in the ooze and partly in the water, he disappeared into his night. Slowly too{{spnd}}perhaps everything is slow at the bottom of the sea{{spnd}}Walsh and I shook hands.<ref>''Seven Miles Down: The Story of the Bathyscaph Trieste'' (1961) by J. Piccard and R. S. Dietz. pages 172–74. Published by Putnam, New York.</ref>}}

Many marine biologists are now skeptical of this supposed sighting, and it is suggested that the creature may instead have been a [[sea cucumber]].<ref>[https://www.theguardian.com/environment/2011/jan/18/james-cameron-dives-deep-avatar "James Cameron dives deep for Avatar"] {{Webarchive|url=https://web.archive.org/web/20170118064643/https://www.theguardian.com/environment/2011/jan/18/james-cameron-dives-deep-avatar |date=18 January 2017}}, ''Guardian'', 18 January 2011</ref><ref>[http://www.nature.com/news/james-cameron-heads-into-the-abyss-1.10246 "James Cameron heads into the abyss"] {{Webarchive|url=https://web.archive.org/web/20120901025830/http://www.nature.com/news/james-cameron-heads-into-the-abyss-1.10246 |date=1 September 2012}}, ''Nature'', 19 March 2012</ref> The video camera on board the ''Kaiko'' probe spotted a sea cucumber, a [[Polynoidae|scale worm]] and a [[shrimp]] at the bottom.<ref>Hadfield, Peter (2 November 1996). [https://www.newscientist.com/article/mg15220548.100-mission-to-marianas--if-mount-everest-was-dropped-into-the-worlds-deepest-trench-it-woulddrown-kaiko-hit-bottom----and-came-back-to-tell-the-tale.html "Mission to Marianas"] {{Webarchive|url=https://web.archive.org/web/20150426053914/http://www.newscientist.com/article/mg15220548.100-mission-to-marianas--if-mount-everest-was-dropped-into-the-worlds-deepest-trench-it-woulddrown-kaiko-hit-bottom----and-came-back-to-tell-the-tale.html |date=26 April 2015}}, ''[[New Scientist]]''.</ref><ref>[https://web.archive.org/web/20081203143936/http://www.time.com/time/magazine/article/0,9171,983295-6,00.html "The last frontier"], ''Time'', 14 August 1995</ref> At the bottom of the Challenger Deep, the ''Nereus'' probe spotted one [[polychaete]] worm (a multi-legged predator) about an inch long.<ref>[http://ns.gov.gu/geography.html Accessed 8 October 2009] {{webarchive|url=https://web.archive.org/web/19961027163532/http://ns.gov.gu/geography.html |date=27 October 1996}} Geography of the ocean floor near Guam with some notes on exploration of the Challenger Deep.</ref>

An analysis of the sediment samples collected by ''Kaiko'' found large numbers of simple organisms at {{convert|10900|m|ft|abbr=on}}.<ref>{{Cite journal|last=Todo |first=Yuko |year=2005 |title=Simple Foraminifera Flourish at the Ocean's Deepest Point |journal=[[Science (journal)|Science]] |volume=307 |issue=5710 |page=689 |doi=10.1126/science.1105407 |pmid=15692042 |s2cid=20003334 |display-authors=etal}}</ref> While similar lifeforms have been known to exist in shallower ocean trenches (> 7,000 m) and on the [[abyssal plain]], the lifeforms discovered in the Challenger Deep possibly represent [[taxon|taxa]] distinct from those in shallower ecosystems.

Most of the organisms collected were simple, soft-shelled [[foraminifera]] (432 species according to National Geographic<ref>{{Cite news |first=John |last=Roach |title=Life Is Found Thriving at Ocean's Deepest Point |url=http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html |work=National Geographic News |date=3 February 2005 |access-date=13 July 2007 |archive-date=22 August 2012 |archive-url=https://web.archive.org/web/20120822121902/http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html}}</ref>), with four of the others representing species of the complex, multi-chambered genera ''[[Leptohalysis]]'' and ''[[Reophax]]''. Eighty-five per cent of the specimens were organic, soft-shelled [[allogromiid]]s, which is unusual compared to samples of [[sediment-dwelling organisms]] from other deep-sea environments, where the percentage of [[Foraminifera#Organic-walled|organic-walled foraminifera]] ranges from 5% to 20%. As small organisms with hard, calcareous shells have trouble growing at extreme depths because of the high solubility of [[calcium carbonate]] in the pressurized water, scientists theorize that the preponderance of soft-shelled organisms in the Challenger Deep may have resulted from the typical [[biosphere]] present when the Challenger Deep was shallower than it is now. Over the course of six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment died out or were unable to adapt to the increasing water pressure and changing environment.<ref>{{cite web|last1=Roach|first1=John|title=Life If Found Thriving at Ocean's Deepest Point|url=http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html|website=National Geographic|publisher=National Geographic Society|access-date=17 February 2015|archive-date=22 August 2012|archive-url=https://web.archive.org/web/20120822121902/http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html}}</ref>

On 17 March 2013, researchers reported data that suggested [[Piezophile|piezophilic]] microorganisms thrive in the Challenger Deep.<ref name="LS-20130317">{{cite web |last=Choi |first=Charles Q. |title=Microbes Thrive in Deepest Spot on Earth |url=http://www.livescience.com/27954-microbes-mariana-trench.html |date=17 March 2013 |publisher=[[LiveScience]] |access-date=17 March 2013 |archive-date=16 April 2020 |archive-url=https://web.archive.org/web/20200416081339/https://www.livescience.com/27954-microbes-mariana-trench.html |url-status=live}}</ref><ref name="NG-20130317">{{cite journal |last1=Glud |first1=Ronnie |last2=Wenzhöfer |first2=Frank |last3=Middleboe |first3=Mathias |last4=Oguri |first4=Kazumasa |last5=Turnewitsch |first5=Robert |last6=Canfield |first6=Donald E. |last7=Kitazato |first7=Hiroshi |title=High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth |doi=10.1038/ngeo1773 |date=17 March 2013 |journal=[[Nature Geoscience]] |volume=6 |issue=4 |page=284 |bibcode = 2013NatGe...6..284G}}</ref> Other researchers reported related studies that microbes thrive inside rocks up to {{convert|1900|ft|m|0|abbr=on|order=flip}} below the sea floor under {{convert|8500|ft|m|0|abbr=on|order=flip}} of ocean off the coast of the northwestern United States.<ref name="LS-20130317" /><ref name="LS-20130314">{{cite web |last=Oskin |first=Becky |title=Intraterrestrials: Life Thrives in Ocean Floor |url=http://www.livescience.com/27899-ocean-subsurface-ecosystem-found.html |date=14 March 2013 |publisher=[[LiveScience]] |access-date=17 March 2013 |archive-date=16 April 2020 |archive-url=https://web.archive.org/web/20200416081350/https://www.livescience.com/27899-ocean-subsurface-ecosystem-found.html |url-status=live}}</ref> According to one of the researchers, "You can find microbes everywhere{{spnd}}they're extremely adaptable to conditions, and survive wherever they are."<ref name="LS-20130317" />

==See also==
{{portal|Oceans}}
*[[Emden Deep]]
*[[Horizon Deep]]
*[[Litke Deep]], closest point to Earth's center
*[[Sirena Deep]] (formerly HMRG Deep)
*[[List of people who descended to Challenger Deep]]

==References==
{{Reflist}}

==External links==
{{commons}}
*{{cite press release |title=Navy Bathyscaph Trieste Makes 37,800-foot Dive |url=http://www.onr.navy.mil/focus/ocean/vessels/submersibles11.htm |archive-url=https://web.archive.org/web/20020418105908/http://www.onr.navy.mil/focus/ocean/vessels/submersibles11.htm |archive-date=18 April 2002 |date=23 January 1960 |publisher=[[U.S. Department of the Navy]]}}
*[https://web.archive.org/web/20090403201531/http://www.marianatrench.com/default.htm Mariana Trench]
*[http://oregonstate.edu/ua/ncs/archives/2016/mar/mariana-trench-seven-miles-deep-ocean-still-noisy-place Mariana Trench: Seven miles deep, the ocean is still a noisy place] {{Webarchive|url=https://web.archive.org/web/20180115175424/http://oregonstate.edu/ua/ncs/archives/2016/mar/mariana-trench-seven-miles-deep-ocean-still-noisy-place |date=15 January 2018 }}

{{Regions of the world}}
{{Coord|11|22.4|N|142|35.5|E|type:waterbody_region:XP|display=title}}

[[Category:Geology of the Pacific Ocean]]
[[Category:Lowest points of the World Ocean]]
[[Category:Landforms of Oceania]]