View source for Hyperion (moon)

{{short description|Moon of Saturn}}
{{Infobox planet
| name       = Hyperion
| mpc_name   = Saturn VII
| pronounced = {{IPAc-en|h|aɪ|ˈ|p|ɪər|i|ə|n}}<ref>{{Cite dictionary |url=http://www.lexico.com/definition/Hyperion |archive-url=https://web.archive.org/web/20200322182521/https://www.lexico.com/definition/hyperion |url-status=dead |archive-date=March 22, 2020 |title=Hyperion |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}<br>{{MW|Hyperion}}</ref><ref name="Latin" group="lower-alpha"/>
| adjectives = Hyperionian {{IPAc-en|ˌ|h|ɪ|p|ər|aɪ|ˈ|oʊ|n|i|ə|n}}<ref>{{Cite web |url=http://saturn.jpl.nasa.gov/science/moons/hyperion/ |title=JPL (ca. 2008) ''Cassini Equinox Mission: Hyperion'' |access-date=2011-01-30 |archive-date=2016-04-10 |archive-url=https://web.archive.org/web/20160410083133/http://saturn.jpl.nasa.gov/science/moons/hyperion/ |url-status=dead }}</ref><ref>Bill Yenne (1987) ''The Atlas of the Solar System'', p. 144</ref>
| named_after= [[Hyperion (mythology)|Ὑπερίων]] ''Hyperīon''<ref name="Latin" group="lower-alpha"/>
| image      = Hyperion true.jpg
| caption    = Hyperion in approximately natural color, as photographed by the ''Cassini'' spacecraft. Bond-Lassell Dorsum arcs across much of Hyperion's face
| discoverer =
  {{plainlist |
* [[William Cranch Bond|William Bond]]
* [[George Phillips Bond|George Bond]]
* [[William Lassell]]
  }}
| discovered = 16 September 1848
| semimajor  = {{convert|1481009|km|mi|abbr=on}}<ref name="nb semimajor" group="lower-alpha" />
| eccentricity = {{val|0.1230061}}<ref>[http://home.gwi.net/~pluto/mpecs/ss07.htm#elements Pluto Project pseudo-MPEC for Saturn VII] {{webarchive|url=https://web.archive.org/web/20060529165828/http://home.gwi.net/~pluto/mpecs/ss07.htm |date=2006-05-29}}</ref>
| period       = {{val|21.276|u=d}}
| inclination  = 0.43° (to Saturn's equator)<ref>[http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Sat_Hyperion&Display=Facts&System=Metric NASA's Solar System Exploration: Saturn: Moons: Hyperion: Facts & Figures] {{webarchive|url=https://web.archive.org/web/20041103232700/http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Sat_Hyperion&Display=Facts&System=Metric |date=2004-11-03 }}</ref><ref>[http://www.mira.org/fts0/planets/100/text/txt002x.htm MIRA's Field Trips to the Stars Internet Education Program: Saturn]</ref><!-- The sse.jpl.nasa.gov pages all say "to the ecliptic" when they mean "to Saturn's equator"; a lot of the quoted masses are also very, very wrong (cut and paste problems, it seems) -->
| satellite_of = [[Saturn]]
| dimensions   = {{convert|360.2 x 266.0 x 205.4|km|mi|abbr=on}}<ref name="Thomas2010" />
| mean_radius  = {{val|135.00|4.00|u=km}}<ref name="Jacobson2022" />
| mass = {{val|5.5510|0.0007|e=18|ul=kg}}<ref name="Jacobson2022">{{cite journal |last1=Jacobson |first1=Robert. A. |title=The Orbits of the Main Saturnian Satellites, the Saturnian System Gravity Field, and the Orientation of Saturn's Pole* |journal=The Astronomical Journal |date=1 November 2022 |volume=164 |issue=5 |pages=199 |doi=10.3847/1538-3881/ac90c9|bibcode=2022AJ....164..199J |s2cid=252992162 |doi-access=free}}</ref>
| density = {{val|0.5386|0.0479|u=g/cm3}}<ref name="Jacobson2022" />
| surface_grav = 0.017–{{val|0.021|ul=m/s2}} depending on location<ref name="Thomas2010" />
| escape_velocity = 45–{{val|99|u=m/s}} depending on location.<ref name="Thomas2007">{{cite journal
  |first1 = P.C. | last1 = Thomas
  |date=2007
  |title=Hyperion's Sponge-like Appearance
  |journal=[[Nature (journal)|Nature]]
  |volume=448 |issue= 7149|pages=50–56
  |doi=10.1038/nature05779
  |pmid=17611535
  |bibcode = 2007Natur.448...50T
  |last2=Armstrong
  |first2=J. W.
  |last3=Asmar
  |first3=S. W.
  |last4=Burns
  |first4=J. A.
  |last5=Denk
  |first5=T.
  |last6=Giese
  |first6=B.
  |last7=Helfenstein
  |first7=P.
  |last8=Iess
  |first8=L.
  |last9=Johnson
  |first9=T. V. | s2cid = 4415537
 | display-authors = 8}}</ref>
| rotation = ~13 d ([[Chaotic rotation|chaotic]])<ref>{{cite web | title= Hyperion In Depth | date=December 2017| url=https://solarsystem.nasa.gov/moons/saturn-moons/hyperion/in-depth/| publisher=NASA | access-date=2019-02-05}}</ref>
| axial_tilt = variable
| albedo = 0.3<ref name=fact>
{{cite web
  |author=D.R. Williams
  |date=18 September 2006
  |title=Saturnian Satellite Fact Sheet
  |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html
  |publisher=[[NASA]]
  |access-date=2007-11-04
}}</ref>
| magnitude = 14.1<ref name="Observatorio ARVAL" />
|single_temperature = 93 [[Kelvin|K]] (−180 C)<ref name="saturn.jpl">{{cite web
  |title=About Saturn & Its Moons: Moons – Hyperion
  |publisher=Cassini @ JPL/NASA
  |url=http://saturn.jpl.nasa.gov/science/moons/hyperion/
  |access-date=2011-01-30
  |archive-url=https://web.archive.org/web/20120604205115/http://saturn.jpl.nasa.gov/science/moons/hyperion/
  |archive-date=2012-06-04
  |url-status=dead
  }}</ref>
}}

'''Hyperion''' {{IPAc-en|h|aɪ|ˈ|p|ɪər|i|ə|n}} is the eighth-largest [[moons of Saturn|moon of Saturn]]. It is distinguished by its highly irregular shape, chaotic rotation, low [[density]], and its unusual sponge-like appearance. It was the first non-[[hydrostatic equilibrium|rounded]] moon to be discovered.

== Discovery == 
Hyperion was independently discovered by [[William Cranch Bond]] and his son [[George Phillips Bond]] in the United States, and [[William Lassell]] in the United Kingdom in September 1848.

== Name == 
The moon is named after the [[Titan (mythology)|Titan]] [[Hyperion (Titan)|Hyperion]], the god of watchfulness and observation, and the elder brother of [[Cronus]] (the Greek equivalent of the [[Roman mythology|Roman god]] [[Saturn (mythology)|Saturn]]). It is also designated ''Saturn&nbsp;VII''. The adjectival form of the name is ''Hyperionian''.

Hyperion's discovery came shortly after [[John Herschel]] had suggested names for the seven previously known satellites of Saturn in his 1847 publication ''Results of Astronomical Observations made at the Cape of Good Hope''.<ref name="Lassell 1848 Observations" /> [[William Lassell]], who saw Hyperion two days after [[William Cranch Bond|William Bond]], had already endorsed Herschel's naming scheme and suggested the name Hyperion in accordance with it.<ref>
{{cite journal
 |author=W. Lassell
 |date=1848<!--- ADS says 1847, but the contents make it abundantly clear this volume was published in 1848; see for example the observations of Flora reported in the lower half of page 197, dated May 1848 --->
 |title=Discovery of a New Satellite of Saturn
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=8 |issue=9 |pages=195–197
 |doi=10.1093/mnras/8.9.195a
 |bibcode=1848MNRAS...8..195L
|url=https://zenodo.org/record/1431913
 |doi-access=free
 }}</ref> He also beat Bond to publication.<ref>
{{cite journal
 |first = W.C. | last = Bond
 |date=1848
 |title=Discovery of a new satellite of Saturn
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=9 |issue=1 |pages=1–2
 |doi=10.1093/mnras/9.1.1
 |bibcode=1848MNRAS...9....1B
| url = https://zenodo.org/record/1431915
 |doi-access=free
 }}</ref>

== Physical characteristics ==
[[File:NotSoHyperHyperion.jpg|thumb|Hyperion compared to [[Ceres (dwarf planet)|Ceres]] and the [[Moon]]<ref name="Thomas2010" />]]

=== Shape ===
Hyperion is one of the largest bodies known to be highly irregularly shaped (non-ellipsoidal, and especially not in [[hydrostatic equilibrium]]) in the [[Solar System]].<ref name="nb larger objects" group="lower-alpha"/> The only larger moon known to be irregular in shape is Neptune's moon [[Proteus (moon)|Proteus]]. Hyperion has about 15% of the mass of [[Mimas (moon)|Mimas]], the least massive known ellipsoidal body. The largest [[Impact crater|crater]] on Hyperion is approximately {{convert|121.57|km|mi|abbr=on}} in diameter and {{convert|10.2|km|mi|abbr=on}} deep. A possible explanation for the irregular shape is that Hyperion is a fragment of a larger body that was broken up by a large impact in the distant past.<ref name="Matthews1992">
{{cite journal
 |author=R.A.J. Matthews
 |date=1992
 |title=The Darkening of Iapetus and the Origin of Hyperion
 |journal=[[Quarterly Journal of the Royal Astronomical Society]]
 |volume=33 |pages=253–258
 |bibcode=1992QJRAS..33..253M
}}</ref> A proto-Hyperion could have been {{convert|350|–|1000|km|mi|abbr=on}} in diameter (which ranges from a little below the size of Mimas to a little below the size of [[Tethys (moon)|Tethys]]).<ref name=Farinella1997>{{cite journal
  |last=Farinella |first=P.
  |author2=Marzari, F. |author3=Matteoli, S.
   |title=The Disruption of Hyperion and the Origin of Titan's Atmosphere
  |journal=Astronomical Journal
  |volume=113 |issue=2 |pages=2312–2316 |date=1997
  |doi=10.1086/118441
  |bibcode=1997AJ....113.2312F
  |doi-access=free}}</ref> Over about 1,000&nbsp;years, ejecta from a presumed Hyperion breakup would have impacted [[Titan (moon)|Titan]] at low speeds, building up [[Volatile (astrogeology)|volatiles]] in the [[atmosphere of Titan]].<ref name="Farinella1997" />

=== Composition ===
[[File:Hyperion in natural colours.jpg|195px|thumb|right|True-color image of Hyperion, taken by the [[Cassini spacecraft|''Cassini'' spacecraft]]]]
Like most of [[Saturn's natural satellites|Saturn's moons]], Hyperion's low [[density]] indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted [[Rubble pile|pile of rubble]] in its physical composition. However, unlike most of Saturn's moons, Hyperion has a low [[albedo]] (0.2–0.3), indicating that it is covered by at least a thin layer of dark material. This may be material from [[Phoebe (moon)|Phoebe]] (which is much darker) that got past [[Iapetus (moon)|Iapetus]]. Hyperion is redder than Phoebe and closely matches the color of the dark material on Iapetus.

Hyperion has a [[porosity]] of about 0.46.<ref name="Thomas2007" /> Although Hyperion is the eighth-largest moon of Saturn, it is only the ninth-most massive. [[Phoebe (moon)|Phoebe]] has a smaller radius, but it is more massive than Hyperion and thus denser.<ref name="Thomas2010" />

=== Surface features ===

{{See also|List of geological features on Hyperion}}

''[[Voyager 2]]'' passed through the Saturn system, but photographed Hyperion only from a distance. It discerned individual craters and an enormous ridge, but was not able to make out the texture of Hyperion's surface. Early images from the ''[[Cassini–Huygens|Cassini]]'' orbiter suggested an unusual appearance, but it was not until ''Cassini'''s first targeted flyby of Hyperion on 25 September 2005 that Hyperion's oddness was revealed in full.

Hyperion's surface is covered with deep, sharp-edged [[impact crater|crater]]s that give it the appearance of a giant sponge. Dark material fills the bottom of each crater. The reddish substance contains long chains of [[carbon]] and [[hydrogen]] and appears very similar to material found on other Saturnian satellites, most notably [[Iapetus (moon)|Iapetus]]. Scientists attribute Hyperion's unusual, sponge-like appearance to the fact that it has an unusually low density for such a large object. Its low density makes Hyperion quite porous, with a weak surface gravity. These characteristics mean impactors tend to compress the surface, rather than excavating it, and most material that is blown off the surface never returns.<ref name="next2015"/>

The latest analyses of data obtained by ''Cassini'' during its flybys of Hyperion in 2005 and 2006 show that about 40 percent of it is empty space. It was suggested in July 2007 that this [[porosity]] allows craters to remain nearly unchanged over the eons. The new analyses also confirmed that Hyperion is composed mostly of water ice with very little rock.<ref>
{{cite web
 |title=Key to Giant Space Sponge Revealed
 |url=http://www.space.com/scienceastronomy/070704_sponge_moon.html
 |work=[[Space.com]]
 |date=4 July 2007
 |access-date=October 26, 2007
}}</ref>

=== Static charge ===
Hyperion's surface is electrically charged and was the first discovered to be so other than the [[Moon]]'s surface.<ref>{{Cite web |last= |title=Cassini Caught in Hyperion's Particle Beam |url=https://www.jpl.nasa.gov/news/cassini-caught-in-hyperions-particle-beam |access-date=2024-02-19 |website=www.jpl.nasa.gov |publisher=NASA Jet Propulsion Laboratory (JPL) |language=en-US}}</ref>

== Orbit and rotation ==
[[File:Animation of Hyperion orbit around Saturn.gif|thumb|right|Animation of Hyperion's orbit.<br />{{legend2|RoyalBlue| Saturn}}{{·}}{{legend2| Magenta | Hyperion}}{{·}}{{legend2|Cyan|Titan}}]]
[[File:Hyperion_false_color.jpg|right|thumb|190x190px|Image of Hyperion processed to bring out details. It was taken by the [[Cassini–Huygens|''Cassini'']] space probe.]]
The ''[[Voyager 2]]'' images and subsequent ground-based [[Photometry (astronomy)|photometry]] indicated that Hyperion's rotation is [[Chaotic rotation|chaotic]], that is, its axis of rotation wobbles so much that its orientation in space is unpredictable. Its [[Lyapunov time]] is around 30 days.<ref>{{cite journal|title=Nonlinear time-series analysis of Hyperion's lightcurves|author=M. Tarnopolski|s2cid=56311141|journal=Astrophysics and Space Science|volume=357|issue = 2|pages=160|doi=10.1007/s10509-015-2379-3|date=May 2015|bibcode=2015Ap&SS.357..160T|arxiv = 1412.2423}}</ref><ref>{{cite journal|title=Influence of a second satellite on the rotational dynamics of an oblate moon|author=M. Tarnopolski|s2cid=118512400|journal=Celestial Mechanics and Dynamical Astronomy|volume=127|issue = 2|pages=121–138|doi=10.1007/s10569-016-9719-7|date=Feb 2017|bibcode=2017CeMDA.127..121T|arxiv=1607.07333}}</ref><ref>{{cite journal|title=Rotation of an oblate satellite: Chaos control|author=M. Tarnopolski|s2cid=119360690|journal=Astronomy & Astrophysics|volume=606|pages=A43|doi=10.1051/0004-6361/201731167|date=Oct 2017|bibcode=2017A&A...606A..43T|arxiv=1704.02015}}</ref> Hyperion, together with [[moons of Pluto|Pluto's moons]] [[Nix (moon)|Nix]] and [[Hydra (moon)|Hydra]],<ref>{{cite journal|title=Resonant interactions and chaotic rotation of Pluto's small moons|author=M. R. Showalter, D. P. Hamilton|s2cid=205243819|journal=Nature|volume=522|issue=7554|pages=45–49|doi=10.1038/nature14469|pmid=26040889|date=Jun 2015|bibcode = 2015Natur.522...45S }}</ref><ref>{{cite news|url=https://www.nytimes.com/2015/06/04/science/space/pluto-moons-orbits-described-in-nature-article.html|title=Astronomers Describe Chaotic Dance of Pluto's Moons|newspaper=New York Times|date=2015-06-03|author=Kenneth Chang}}</ref> is among only a few moons in the Solar System known to rotate chaotically, although it is expected to be common in [[binary asteroid]]s.<ref>{{cite journal |last1=Nadoushan |first1=M. J. |last2=Assadian |first2=N. |date=2015 |title=Widespread chaos in rotation of the secondary asteroid in a binary system |journal=Nonlinear Dynamics |volume= 81|issue= 4|pages=2031 |doi=10.1007/s11071-015-2123-0|bibcode = 2015NonLD..81.2031J |s2cid=124747289 }}</ref> It is also the only [[regular moon|regular planetary natural satellite]] in the Solar System known to not be [[Tidal locking|tidally locked]].

Hyperion is unique among the large moons in that it is very irregularly shaped, has a fairly eccentric orbit, and is near a much larger moon, [[Titan (moon)|Titan]]. These factors combine to restrict the set of conditions under which a stable rotation is possible. The 3:4 [[orbital resonance]] between Titan and Hyperion may also make a chaotic rotation more likely. The fact that its rotation is not locked probably accounts for the relative uniformity of Hyperion's surface, in contrast to many of [[Saturn's natural satellites|Saturn's other moons]], which have contrasting trailing and leading hemispheres.<ref>
{{cite journal
 |first1 = J. | last1 = Wisdom | first2 = S.J. | last2 = Peale | first3 = F. | last3 = Mignard
 |date=1984
 |title=The chaotic rotation of Hyperion
 |journal=[[Icarus (journal)|Icarus]]
 |volume=58 |issue= 2|pages=137–152
 |bibcode=1984Icar...58..137W
 |doi=10.1016/0019-1035(84)90032-0
| citeseerx = 10.1.1.394.2728 }}</ref>

== Exploration ==

Hyperion has been imaged several times from moderate distances by the [[Cassini–Huygens|''Cassini'' orbiter]]. The first close targeted flyby occurred at a distance of {{convert|500|km|abbr=on}} on 26 September 2005.<ref name="next2015" /> ''Cassini'' made another close approach to Hyperion on 25 August 2011 when it passed {{convert|25000|km|abbr=on}} from Hyperion, and third close approach was on 16 September 2011, with closest approach of {{convert|58000|km|abbr=on}}.<ref>{{cite web|title=Saturn's Odd Pockmarked Moon Revealed in New Photos|date=30 August 2011 |url=http://www.space.com/12774-saturn-moon-hyperion-cassini-flyby-photos.html|publisher=Space.com|access-date=31 August 2011}}</ref> ''Cassini'''s last flyby was on 31 May 2015 at a distance of about {{convert|34000|km|abbr=on}}.<ref name="next2015">{{cite news |url=http://www.jpl.nasa.gov/news/news.php?feature=4606 |title=Cassini Prepares for Last Up-close Look at Hyperion |work=Jet Propulsion Laboratory |date=28 May 2015 |access-date=2015-05-29}}</ref>

== See also ==
* [[Chaotic rotation]]
* [[Saturn in fiction#Moons|Hyperion in fiction]]
* [[Moons of Saturn]]
* [[List of geological features on Hyperion]]

== Notes ==

{{Reflist
| group = lower-alpha
| refs =

<ref name="Latin">
From the long 'i' in Latin ''Hyperīon'', one might expect the name to be stressed on the 'i' in English, {{IPAc-en|ˌ|h|ɪ|p|ə|ˈ|r|aɪ|ə|n}}, and indeed that pronunciation is recommended in Noah Webster (1884) ''A Practical Dictionary of the English Language'', but recent sources universally stress the name of the 'e', as indeed do many older sources, such as [[Hyperion (poem)|Keats' poem]].
</ref>
<ref name="nb semimajor">
Computed from period, using the [https://archive.today/20110520031937/http://www.minorplanetcenter.org/iau/NatSats/NaturalSatellites.html IAU-MPC NSES] μ value.
</ref>
<ref name="nb larger objects">
There are [[List of notable asteroids#Largest by diameter|about ten asteroids]] and an unknown number of irregular [[Trans-Neptunian object]]s larger than Hyperion.
</ref>

}}

== References ==

{{Reflist
| colwidth = 30em
| refs =

<ref name="Thomas2010">{{cite journal |doi=10.1016/j.icarus.2010.01.025 |last1=Thomas |first1=P. C. |date=July 2010 |title=Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission |journal=Icarus |volume=208 |issue=1 |pages=395–401 |url=http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf |bibcode=2010Icar..208..395T |access-date=2015-09-04 |archive-date=2011-09-27 |archive-url=https://web.archive.org/web/20110927185355/http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf |url-status=dead}}</ref>

<ref name="Observatorio ARVAL">{{cite web
| author = Observatorio ARVAL
| title = Classic Satellites of the Solar System
| publisher = Observatorio ARVAL
| date = April 15, 2007
| url = http://www.oarval.org/ClasSaten.htm
| access-date = 2011-12-17
| ref = {{sfnRef|Observatorio ARVAL}}
| archive-url = https://web.archive.org/web/20110920010842/http://www.oarval.org/ClasSaten.htm
| archive-date = September 20, 2011
| url-status = dead
}}</ref>

<ref name="Lassell 1848 Observations">
{{cite journal
| last = Lassell
| first = W.
| author-link = William Lassell
| date = 14 January 1848
| title = Observations of satellites of Saturn
| journal = [[Monthly Notices of the Royal Astronomical Society]]
| volume = 8
| issue = 3
| pages = 42–43
| url = http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html
| access-date = 2011-12-18
| bibcode = 1848MNRAS...8...42L
| doi = 10.1093/mnras/8.3.42
| doi-access = free
}}
</ref>

}}

== External links ==

{{Commons category|Hyperion}}
{{Spoken Wikipedia|Hyperion_(moon).ogg|date=2010-01-09}}
* [https://web.archive.org/web/20120604205115/http://saturn.jpl.nasa.gov/science/moons/hyperion/ ''Cassini'' mission Hyperion page]
* [https://web.archive.org/web/20190713072219/https://solarsystem.nasa.gov/moons/saturn-moons/hyperion/in-depth/] at [http://solarsystem.nasa.gov NASA's Solar System Exploration site]
* [http://www.planetary.org/multimedia/space-images/saturn/photos-of-hyperion-with-place-names.html The Planetary Society: Hyperion]
* [http://www.nasa.gov/multimedia/imagegallery/image_feature_749.html NASA: Saturn's Hyperion, A Moon With Odd Craters]
* [http://ciclops.org/search.php?x=20&y=7&search=Hyperion ''Cassini'' images of Hyperion] {{Webarchive|url=https://web.archive.org/web/20110813151202/http://ciclops.org/search.php?x=20&y=7&search=Hyperion |date=2011-08-13 }}
* [http://photojournal.jpl.nasa.gov/target/Hyperion Images of Hyperion at JPL's Planetary Photojournal]
* [https://planetarynames.wr.usgs.gov/Page/HYPERION/target Hyperion nomenclature] from the [http://planetarynames.wr.usgs.gov USGS planetary nomenclature page]

{{Moons of Saturn|state=uncollapsed}}
{{Solar System moons (compact)}}
{{Saturn}}
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[[Category:Hyperion (moon)| ]]
[[Category:Moons of Saturn]]
[[Category:Discoveries by William Cranch Bond]]
[[Category:Astronomical objects discovered in 1848|18480916]]
[[Category:Chaotic maps]]
[[Category:Moons with a prograde orbit]]