View source for Near-Earth object

{{Redirect-distinguish|NEAs|North East Ambulance Service}}
{{short description|Small Solar System body with an orbit that can bring it close to Earth}}
{{Good article}}
{{Infobox astronomical formation
|name=Near-Earth object
|image={{Multiple image
| perrow = 2/1
| total_width = 300
| align = center
| image1 = Eros - PIA02923 (color).jpg
| caption1 = The near-Earth asteroid [[433 Eros]]
| image2 = The VLT images the very faint Near-Earth Object 2009 FD.jpg
| caption2 = Very faint near-Earth asteroid {{mpl|2009 FD}} as seen by the [[Very Large Telescope|VLT]] telescope
| image3 = Comet Hartley 2.jpg
| caption3 = Nucleus of near-Earth comet [[103P/Hartley]] as seen by NASA's ''[[Deep Impact (spacecraft)|Deep Impact]]'' probe 
}}
|where=within 1.3 [[Astronomical unit|AU]] from the [[Sun]]
|thing=[[Small Solar System body]]
|commonscat=Near-Earth objects
|qid=Q265392
|head=
}}
{{Pie chart
| caption = 37,000+ known NEOs, divided into several orbital subgroups<ref name="neo-jpl-stats" />
| label1 = [[Apollo asteroid|Apollos]]: 21,132
| value1 = 56.54
| color1 = #009a39
| label2 = [[Amor asteroid|Amors]]: 13,137
| value2 = 35.15
| color2 = #66CCFF
| label3 = [[Aten asteroid|Atens]]: 2,952
| value3 = 7.90
| color3 = #f7c35a
| label4 = [[Comet]]s: 123
| value4 = 0.33
| color4 = #de2821
| label5 = [[Atira asteroid|Atiras]]: 34
| value5 = 0.09
| color5 = black
}}

A '''near-Earth object''' ('''NEO''') is any [[small Solar System body]] orbiting the [[Sun]] whose closest approach to the Sun ([[Apsis|perihelion]]) is less than 1.3 times the Earth–Sun distance ([[astronomical unit]], AU).<ref name="CNEOS-NEO-groups"/> This definition applies to the object's orbit around the Sun, rather than its current position, thus an object with such an orbit is considered an NEO even at times when it is far from making a close approach of [[Earth]]. If an NEO's orbit crosses the Earth's orbit, and the object is larger than {{convert|140|meter|ft|-1}} across, it is considered a [[potentially hazardous object]] (PHO).<ref name="CHAPMAN04"/> Most known PHOs and NEOs are [[asteroid]]s, but about a third of a percent are [[comet]]s.<ref name="neo-jpl-stats" />

There are over 37,000 known [[#Near-Earth asteroids|near-Earth asteroids]] (NEAs) and over 120 known short-period [[#Near-Earth comets|near-Earth comets]] (NECs).<ref name="neo-jpl-stats" /> A number of solar-orbiting [[meteoroid]]s were large enough to be tracked in space before striking Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of Earth.<ref name="BROWN02">{{cite news |first=Richard |last=Monastersky |title=The Call of Catastrophes |work=Science News Online |date=March 1, 1997  |url=https://www.sciencenews.org/archive/call-catastrophes |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20040313165341/http://www.sciencenews.org/pages/sn_arc97/75th/rm_essay.htm |archive-date=March 13, 2004}}</ref> Asteroids as small as {{convert|20|m|ft}} in diameter can cause significant damage to the local environment and human populations.<ref>{{Cite journal |last1=Rumpf |first1=Clemens M.|last2=Lewis |first2=Hugh G.|last3=Atkinson |first3=Peter M. |date=March 23, 2017 |title=Asteroid impact effects and their immediate hazards for human populations |journal=[[Geophysical Research Letters]] |volume=44 |issue=8 |pages=3433–3440 |doi=10.1002/2017gl073191 |issn=0094-8276 |arxiv=1703.07592 |bibcode=2017GeoRL..44.3433R |s2cid=34867206}}</ref> Larger asteroids penetrate the atmosphere to the surface of the Earth, producing craters if they impact a continent or [[tsunami]]s if they impact the sea. Interest in NEOs has increased since the 1980s because of greater awareness of this risk. [[Asteroid impact avoidance]] by deflection is possible in principle, and methods of mitigation are being researched.<ref name="tsr20120514"/>

Two scales, the simple [[Torino scale]] and the more complex [[Palermo scale]], rate the risk presented by an identified NEO based on the probability of it impacting the Earth and on how severe the consequences of such an impact would be. Some NEOs have had temporarily positive Torino or Palermo scale ratings after their discovery. Since 1998, the United States, the European Union, and other nations have been scanning the sky for NEOs in an effort called [[Spaceguard]].<ref name="spaceguard-2004" /> The initial US Congress mandate to [[NASA]] to catalog at least 90% of NEOs that are at least {{convert|1|km|mi}} in diameter, sufficient to cause a global catastrophe, was met by 2011.<ref name="pia14734" /> In later years, the survey effort was expanded<ref name="law-109-155"/> to include smaller objects<ref name="ETech"/> which have the potential for large-scale, though not global, damage.

NEOs have low surface gravity, and many have Earth-like orbits that make them easy targets for spacecraft.<ref name="USAToday-NEA"/><ref name="wired20130323"/> {{As of|2024|12}}, five near-Earth comets<ref name="TaskForceReport"/><ref name="DeepImpactHartley"/><ref name="newsci20160930"/> and six near-Earth asteroids,<ref name="Eros-NEAR"/><ref name="Toutatis-Change"/><ref name="Spacecom-Hayabusa2-2019"/><ref name="space-osiris-overview"/><ref name="NASA220927"/> one of them with a moon,<ref name="NASA220927"/> have been visited by spacecraft. Samples of three have been returned to Earth,<ref name="BBC-Hayabusa2"/><ref name="space-osiris-sample"/> and one successful deflection test was conducted.<ref name="NASA221215"/> Similar missions are in progress. Preliminary plans for commercial [[asteroid mining]] have been drafted by private startup companies, but few of these plans were pursued.<ref name="Forbes210831"/>

== Definitions ==
[[File:Potentially Hazardous Asteroids 2013.png|thumb|Plot of orbits of known [[Potentially hazardous object|potentially hazardous asteroids]] (size over {{convert|460|ft|m|order=flip|abbr=on}} and passing within {{convert|4.7|e6mi|e6km|order=flip|abbr=on}} of Earth's orbit) as of early 2013 ([[:File:PIA17041-Orbits-PotentiallyHazardousAsteroids-Early2013.jpg|alternate image]])]]

Near-Earth objects (NEOs) are formally defined by the [[International Astronomical Union]] (IAU) as all [[Small Solar System body|small Solar System bodies]] with orbits around the Sun that are at least partially closer than 1.3 [[astronomical unit]]s (AU; Sun–Earth distance) from the Sun.<ref name="IAU-NEOs"/> This definition excludes larger bodies such as [[planet]]s, like [[Venus]]; [[natural satellite]]s which orbit bodies other than the Sun, like Earth's [[Moon]]; and artificial bodies orbiting the Sun. A small Solar System body can be an [[asteroid]] or a [[comet]], thus an NEO is either a near-Earth asteroid (NEA) or a near-Earth comet (NEC). The organisations cataloging NEOs further limit their definition of NEO to objects with an orbital period under 200 years, a restriction that applies to comets in particular,<ref name="CNEOS-NEO-groups">{{cite web |title=NEO Basics. NEO Groups |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/about/neo_groups.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101153312/https://cneos.jpl.nasa.gov/about/neo_groups.html |archive-date=January 1, 2025}}</ref><ref name="NEOCC-DA">{{cite web |title=Definitions & Assumptions |publisher=[[European Space Agency|ESA]] [[Near-Earth Object Coordination Centre|NEOCC]] |url=https://neo.ssa.esa.int/definitions-assumptions |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101040757/https://neo.ssa.esa.int/definitions-assumptions |archive-date=January 1, 2025}}</ref> but this approach is not universal.<ref name="IAU-NEOs"/> Some authors further restrict the definition to orbits that are at least partly further than 0.983 AU away from the Sun.<ref name="MorbidelliAstIII"/><ref>{{Cite journal |last1=Waszczak |first1=Adam |last2=Prince |first2=Thomas A. |last3=Laher |first3=Russ |last4=Masci |first4=Frank |last5=Bue |first5=Brian |last6=Rebbapragada |first6=Umaa |last7=Barlow |first7=Tom |last8=Jason Surace |last9=Helou |first9=George |display-authors=2 |date=2017 |title=Small Near-Earth Asteroids in the Palomar Transient Factory Survey: A Real-Time Streak-detection System |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=129 |issue=973 |at=part 034402 |doi=10.1088/1538-3873/129/973/034402 |issn=1538-3873 |arxiv=1609.08018|bibcode=2017PASP..129c4402W |s2cid=43606524}}</ref> NEOs are thus not necessarily currently near the Earth, but they can potentially approach the Earth relatively closely. Many NEOs have complex orbits due to constant perturbation by the Earth's gravity, and some of them can temporarily change from an orbit around the Sun to one around the Earth, but the term is applied flexibly for these objects, too.<ref name="ST111230"/>

The orbits of some NEOs intersect that of the Earth, so they pose a collision danger.<ref name="CHAPMAN04">{{cite journal |first=Clark R. |last=Chapman |title=The hazard of near-Earth asteroid impacts on earth |journal=[[Earth and Planetary Science Letters]] |volume=222 |issue=1 |pages=1–15 |date=May 2004 |doi=10.1016/j.epsl.2004.03.004 |bibcode=2004E&PSL.222....1C}}</ref> These are considered [[potentially hazardous object]]s (PHOs) if their estimated diameter is above 140 meters. PHOs include potentially hazardous asteroids (PHAs).<ref name="MPC-PHA-list"/><ref>{{cite journal |last1=Perna |first1=D. |last2=Barucci |first2=M. A. |last3=Fulchignoni |first3=M. |title=The near-Earth objects and their potential threat to our planet |journal=[[The Astronomy and Astrophysics Review]] |date=2013 |volume=21 |issue=1 |pages=65 |doi=10.1007/s00159-013-0065-4|bibcode=2013A&ARv..21...65P}}</ref> PHAs are defined based on two parameters relating to respectively their potential to approach the Earth dangerously closely and the estimated consequences that an impact would have if it occurs.<ref name="CNEOS-NEO-groups"/> Objects with both an Earth [[minimum orbit intersection distance]] (MOID) of 0.05&nbsp;AU or less and an [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] of 22.0 or brighter (a rough indicator of large size) are considered PHAs. Objects that either cannot approach closer to the Earth than {{convert |0.05 |AU |km mi |abbr=on |lk=in}}, or which are fainter than H = 22.0 (about {{convert|140|m|ft|abbr=on|lk=off}} in diameter with assumed [[albedo]] of 14%), are not considered PHAs.<ref name="CNEOS-NEO-groups"/>

== History of human awareness of NEOs ==
[[File:PSM V76 D020 Path of halley comet.png|thumb|1910 drawing of the path of [[Halley's Comet]]]]
[[File:Eros - PIA02923 (color).jpg|thumb|The near-Earth asteroid [[433 Eros]] as seen by the probe [[NEAR Shoemaker]]]]
The first near-Earth objects to be observed by humans were comets. Their extraterrestrial nature was recognised and confirmed only after [[Tycho Brahe]] tried to measure the distance of a comet through its [[parallax]] in 1577 and the lower limit he obtained was well above the Earth diameter; the periodicity of some comets was first recognised in 1705, when [[Edmond Halley]] published his orbit calculations for the returning object now known as [[Halley's Comet]].<ref name="Halley-synopsis">{{cite book |last=Halley |first=Edmund |date=1705 |title=A synopsis of the astronomy of comets |location=London |publisher=John Senex |url=https://library.si.edu/digital-library/book/synopsisofastron00hall |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171201055040/https://library.si.edu/digital-library/book/synopsisofastron00hall |archive-date=December 1, 2017}}</ref> The 1758–1759 return of Halley's Comet was the first comet appearance predicted.<ref>{{cite book |last=Stoyan |first=Ronald |title=Atlas of Great Comets |date=2015 |location=Cambridge |publisher=Cambridge University Press |pages=101–103 |isbn=978-1-107-09349-2 |url=https://books.google.com/books?id=WAZEBgAAQBAJ&pg=PA101 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20180301114413/https://books.google.com/books?id=WAZEBgAAQBAJ&pg=PA101&lpg=PA101 |archive-date=March 1, 2018}}</ref>

The extraterrestrial origin of [[Meteoroid|meteors]] (shooting stars) was only recognised on the basis of the analysis of the 1833 [[Leonids|Leonid meteor shower]] by astronomer [[Denison Olmsted]]. The 33-year period of the Leonids led astronomers to suspect that they originate from a comet that would today be classified as an NEO, which was confirmed in 1867, when astronomers found that the newly discovered comet [[55P/Tempel–Tuttle]] has the same orbit as the Leonids.<ref>{{cite journal |first=S. J. |last=Dick |title=Observation and interpretation of the Leonid meteors over the last millennium |journal=[[Journal of Astronomical History and Heritage]] |volume=1 |issue=1 |pages=1–20 |date=June 1998 |doi=10.3724/SP.J.1440-2807.1998.01.01 |bibcode=1998JAHH....1....1D}}</ref>

The first near-Earth asteroid to be discovered was [[433 Eros]] in 1898.<ref name=Scholl>{{Cite journal |last1=Scholl |first1=Hans |author-link=Hans Scholl (astronomer) |last2=Schmadel |first2=Lutz D. |title=Discovery Circumstances of the First Near-Earth Asteroid (433) Eros |journal=Acta Historica Astronomiae |bibcode=2002AcHA...15..210S |volume=15 |pages=210–220 |date=2002}}</ref> The asteroid was subject to several extensive observation campaigns, primarily because measurements of its orbit enabled a precise determination of the then imperfectly known distance of the Earth from the Sun.<ref>{{cite web |title=Eros comes on stage, finally a useful asteroid |publisher=Johns Hopkins University Applied Physics Laboratory |url=http://near.jhuapl.edu/eros/history/eros_useful.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203073123/https://near.jhuapl.edu/eros/history/eros_useful.html |archive-date=December 3, 2024}}</ref>

=== Encounters with Earth ===

If a near-Earth object is near the part of its orbit closest to Earth's at the same time Earth is at the part of its orbit closest to the near-Earth object's orbit, the object has a close approach, or, if the orbits intersect, could even impact the Earth or its atmosphere.

==== Close approaches ====
{{main|List of asteroid close approaches to Earth}}

{{As of|2019|5}}, only 23 comets have been observed to pass within {{convert|0.1|AU|km mi|abbr=on|lk=off}} of Earth, including 10 which are or have been short-period comets.<ref name="closest-NEC"/> Two of these near-Earth comets, Halley's Comet and [[73P/Schwassmann–Wachmann]], have been observed during multiple close approaches.<ref name="closest-NEC"/> The closest observed approach was 0.0151&nbsp;AU (5.88&nbsp;LD) for [[Lexell's Comet]] on July 1, 1770.<ref name="closest-NEC" /> After an orbit change due to a close approach of Jupiter in 1779, this object is no longer an NEC. The closest approach ever observed for a current short-period NEC is 0.0229&nbsp;AU (8.92&nbsp;LD) for [[55P/Tempel–Tuttle|Comet Tempel–Tuttle]] in 1366.<ref name="closest-NEC"/> Orbital calculations show that [[P/1999 J6 (SOHO)]], a faint [[sungrazing comet]] and confirmed short-period NEC observed only during its close approaches to the Sun,<ref>{{cite journal |last1=Sekanina |first1=Zdenek |last2=Chodas |first2=Paul W. |title=Origin of the Marsden and Kracht Groups of Sunskirting Comets. I. Association with Comet 96P/Machholz and Its Interplanetary Complex |journal=The Astrophysical Journal Supplement Series |volume=151 |issue=2 |pages=551–586 |date=December 2005 |doi=10.1086/497374 |bibcode=2005ApJS..161..551S |s2cid=85442034}}</ref> passed Earth undetected at a distance of 0.0120&nbsp;AU (4.65&nbsp;LD) on June 12, 1999.<ref>{{cite web |title=Small-Body Database Lookup. P/1999 J6 (SOHO) |date=April 16, 2021 |publisher=NASA/JPL |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1999%20J6&view=OPC |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175145/https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1999%20J6&view=OPC |archive-date=January 1, 2025}}</ref>

In 1937, {{convert|800|m|ft|abbr=on}} asteroid [[69230 Hermes]] was discovered when it passed the Earth at twice the [[Lunar distance|distance of the Moon]].<ref name="RadarHermes">{{cite web |title=Radar observations of long-lost asteroid 1937 UB (Hermes) |publisher=[[University of California, Los Angeles|UCLA]] |url=http://www2.ess.ucla.edu/~jlm/research/NEAs/Hermes/ |access-date=January 26, 2024 |url-status=dead |archive-url=https://web.archive.org/web/20230123110938/http://www2.ess.ucla.edu/~jlm/research/NEAs/Hermes/ |archive-date=January 23, 2023}}</ref> On June 14, 1968, the {{convert|1.4|km|mi|abbr=on}} diameter asteroid [[1566 Icarus]] passed Earth at a distance of {{convert |0.0425 |AU |km |abbr=on |lk=off}}, or 16.5 times the distance of the Moon.<ref name=jpl-close>{{cite web |title=Small-Body Database Lookup. 1566 Icarus (1949 MA) |publisher=NASA/JPL |date=August 4, 2024 |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1566&view=OPC |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250103085945/https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1566&view=OPC |archive-date=January 3, 2025}}</ref> During this approach, Icarus became the first minor planet to be observed using [[radar]].<ref name="Pettengill-1969">{{Cite journal |display-authors=6 |first1=G. H. |last1=Pettengill |first2=I. I. |last2=Shapiro |first3=M. E. |last3=Ash |first4=R. P. |last4=Ingalls |first5=L. P. |last5=Rainville |first6=W. B. |last6=Smith |first7=M. L. |last7=Stone |date=May 1969 |title=Radar observations of Icarus |journal=[[Icarus (journal)|Icarus]] |volume=10 |issue=3 |pages=432–435 |bibcode=1969Icar...10..432P |doi= 10.1016/0019-1035(69)90101-8 |issn=0019-1035}}</ref><ref name="Goldstein-1968">{{Cite journal |last=Goldstein |first= R. M. |date=November 1968 |title=Radar Observations of Icarus |journal=[[Science (journal)|Science]] |volume=162 |issue=3856 |pages=903–904 |bibcode=1968Sci...162..903G |doi=10.1126/science.162.3856.903 |pmid=17769079|s2cid=129644095}}</ref> This was the first close approach predicted years in advance, since Icarus had been discovered in 1949.<ref name="Marsden1998"/> The first near-Earth asteroid known to have passed Earth closer than the distance of the Moon was {{mpl|1991 BA|}}, a {{convert|5|-|10|m|ft|abbr=on}} body which passed at a distance of {{convert|170,000|km|mi|abbr=on}}.<ref>{{cite journal |first1=J. V. |last1=Scotti |first2=D. L. |last2=Rabinowitz |first3=B. G. |last3=Marsden |title=Near miss of the Earth by a small asteroid |journal=[[Nature (journal)|Nature]] |volume=354 |pages=287–289 |date=November 28, 1991 |issue=6351 |doi=10.1038/354287a0|bibcode=1991Natur.354..287S}}</ref> As NEA surveys were enhanced, at least one such object was observed each year from 2001, at least a dozen from 2005, and over a hundred from 2020.<ref name="closest-NEA"/><ref name="NEO-close"/>

As astronomers became able to discover ever smaller and fainter and ever more numerous near-Earth objects, they began to routinely observe and catalogue close approaches.<ref name="closest-NEA"/><ref name="NEO-close"/> {{As of|2024|12}}, the closest approach without atmospheric or ground impact ever detected was an encounter with {{convert|5|-|11|m|ft|abbr=on}} asteroid {{mpl|2020 VT|4}} on November 14, 2020,<ref name="NEO-close"/> with a minimum distance of about {{convert|6750|km|mi|abbr=on}} from the Earth's centre, or about {{convert|380|km|mi|abbr=on}} above its surface.<ref name="EarthSky">{{cite news |first=Eddie |last=Irizarry |title=This asteroid just skimmed Earth's atmosphere |work=[[Earth & Sky|EarthSky]] |date= November 16, 2020 |url=https://earthsky.org/space/asteroid-2020-vt4-skimmed-atmosphere-fri-nov-13-2020 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241202233126/https://earthsky.org/space/asteroid-2020-vt4-skimmed-atmosphere-fri-nov-13-2020/ |archive-date=December 2, 2024}}</ref> On November 8, 2011, asteroid {{mpl|(308635) 2005 YU|55}}, relatively large at about {{convert|400|m|ft|abbr=on}} in diameter, passed within {{convert|324930|km|mi|abbr=on}} (0.845 [[lunar distance]]s) of Earth.<ref>{{cite web |title=Small-Body Database Lookup. 308635 (2005 YU55) |date=January 7, 2022 |publisher=NASA/JPL |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2005YU55&view=OPC |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175145/https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2005YU55&view=OPC |archive-date=January 1, 2025}}</ref> On February 15, 2013, the {{convert|30|m|ft|abbr=on}} asteroid [[367943 Duende]] ({{mp|2012 DA|14}}) passed approximately {{convert|27700|km|mi|abbr=on}} above the surface of Earth, closer than satellites in geosynchronous orbit.<ref name="Duende-BBC">{{cite news |first=Jason |last=Palmer |title=Asteroid 2012 DA14 in record-breaking Earth pass |work=BBC News |publisher=[[BBC]] |date=February 15, 2013 |url=https://www.bbc.com/news/science-environment-21442863 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20180217085054/http://www.bbc.com/news/science-environment-21442863 |archive-date=February 17, 2018}}</ref> The asteroid was not visible to the unaided eye. This was the first sub-lunar close passage of an object discovered during a previous passage, and was thus the first to be predicted well in advance.<ref name="Duende-predict">{{cite news |first1=Paul |last1=Chodas |first2=Jon |last2=Giorgini |first3=Don |last3=Yeomans |name-list-style=amp |title=Near-Earth Asteroid {{mp|2012 DA|14}} to Miss Earth on February 15, 2013 |date=March 6, 2012 |work=News |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news174.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171222113153/https://cneos.jpl.nasa.gov/news/news174.html |archive-date=December 22, 2017}}</ref> On October 8, 2025, asteroid 2025 TN2, approximately 87 feet (≈27 m) in diameter, passed safely by Earth at a distance of 1.34 million km (≈0.00895 AU). On the same day, three additional small asteroids — 2025 SJ29, 2025 TF1, and 2020 QU5, measuring about 55 ft, 65 ft, and 81 ft respectively — also made close approaches, all without any risk of impact.<ref>{{Cite web |date=2025-10-09 |title=Aeroplane-sized asteroids approaching earth fast. Check details from NASA |url=https://indianexpress.com/article/technology/science/aeroplane-sized-asteroids-approaching-earth-fast-check-details-from-nasa-10294637/ |access-date=2025-10-09 |website=The Indian Express |language=en}}</ref>

{{wide image|File:Objects_between_earth_and_moon.jpg|2250px|Diagram showing spacecraft and asteroids (past and future) between the Earth and the Moon}}

==== Earth-grazers ====

Some small asteroids that enter the upper atmosphere of Earth at a shallow angle remain intact and leave the atmosphere again, continuing on a solar orbit. During the passage through the atmosphere, due to the burning of its surface, such an object can be observed as an [[Earth-grazing fireball]].

On August 10, 1972, a meteor that became known as the [[1972 Great Daylight Fireball]] was witnessed by many people and even filmed as it moved north over the [[Rocky Mountains]] from the U.S. Southwest to Canada.<ref>{{cite web |url=https://www.youtube.com/watch?v=7M8LQ7_hWtE |title=Grand Teton Meteor (video) |work=[[YouTube]] |date=10 November 2007 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170214110154/https://www.youtube.com/watch?v=7M8LQ7_hWtE |archive-date=February 14, 2017}}</ref> It passed within {{convert|58|km|mi|abbr=on}} of the Earth's surface.<ref>{{cite journal |first=Z. |last=Ceplecha |title=Earth-grazing daylight fireball of August 10, 1972 |date=March 1994 |journal=[[Astronomy & Astrophysics]] |volume=283 |issue=1 |pages=287−288 |bibcode=1994A&A...283..287C}}</ref>

On October 13, 1990, [[Earth-grazing meteoroid of 13 October 1990|Earth-grazing meteoroid EN131090]] was observed above Czechoslovakia and Poland, moving at {{convert|41.74|km/s|mph km/h|0|abbr=on}} along a {{convert|409|km|mi|adj=on|abbr=on}} trajectory from south to north. The closest approach to the Earth was {{convert|98.67|km|mi|abbr=on}} above the surface. It was captured by two all-sky cameras of the [[European Fireball Network]], which for the first time enabled geometric calculations of the orbit of such a body.<ref name="AA">{{cite journal |last1=Borovička |first1=J. |last2=Ceplecha |first2=Z. |title=Earth-grazing fireball of October 13, 1990 |journal=Astronomy & Astrophysics |volume=257 |issue=1 |pages=323–328 |date=April 1992 |bibcode=1992A&A...257..323B |issn=0004-6361}}</ref>

==== Impacts ====
{{main|Impact event}}
{{see also|List of predicted asteroid impacts on Earth|List of bolides}}

When a near-Earth object impacts Earth, objects up to a few tens of metres across ordinarily explode in the [[Mesosphere|upper atmosphere]] (most of them harmlessly), with most or all of the solids [[Evaporation|vaporized]] and only small amounts of meteorites arriving to the Earth surface. Larger objects, by contrast, hit the water surface, forming [[tsunami]] waves, or the solid surface, forming [[impact crater]]s.<ref>{{Cite journal |last1=Chapman |first1= Clark R. |last2=Morrison |first2= David |name-list-style=amp |title=Impacts on the Earth by asteroids and comets: Assessing the hazard |journal=Nature |volume=367 |issue=6458 |pages=33–40 |date=January 6, 1994 |bibcode=1994Natur.367...33C |doi=10.1038/367033a0|s2cid=4305299 |url=https://zenodo.org/records/1233151/files/article.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240702165419/https://zenodo.org/records/1233151/files/article.pdf |archive-date=July 2, 2024}}</ref>

The frequency of impacts of objects of various sizes is estimated on the basis of orbit simulations of NEO populations, the frequency of impact craters on the Earth and the Moon, and the frequency of close encounters.<ref name="Collins2005">{{cite journal |last1=Collins |first1=Gareth S. |last2=Melosh |first2=H. Jay |last3=Marcus |first3=Robert A. |title=Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth |journal=[[Meteoritics & Planetary Science]] |volume=40 |number=6 |pages=817–840 |date=June 2005 |doi=10.1111/j.1945-5100.2005.tb00157.x |url=https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/effects.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241217213340/https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/effects.pdf |archive-date=December 17, 2024 |bibcode=2005M&PS...40..817C |hdl=10044/1/11554 |s2cid=13891988 |hdl-access=free}}</ref><ref name="Asher2005">{{cite journal |last1=Asher |first1=D. J. |last2=Bailey |first2=M. |last3=Emelʹyanenko |first3=V. |last4=Napier |first4=W. |title=Earth in the Cosmic Shooting Gallery |journal=[[The Observatory (journal)|The Observatory]] |volume=125 |issue=2 |pages=319–322 |date=October 2005 |bibcode=2005Obs...125..319A}}</ref> The study of impact craters indicates that impact frequency has been more or less steady for the past 3.5&nbsp;billion years, which requires a steady replenishment of the NEO population from the [[asteroid main belt]].<ref name="MorbidelliAstIII"/> One impact model based on widely accepted NEO population models estimates the average time between the impact of two stony asteroids with a diameter of at least {{convert|4|m|ft|abbr=on}} at about one year; for asteroids {{convert|7|m|ft|abbr=on}} across (which impacts with as much energy as the atomic bomb dropped on [[Atomic bombings of Hiroshima and Nagasaki|Hiroshima]], approximately 15 kilotonnes of TNT) at five years, for asteroids {{convert|60|m|ft|abbr=on}} across (an impact energy of 10 [[megatons]], comparable to the [[Tunguska event]] in 1908) at 1,300 years, for asteroids {{convert|1|km|mi|abbr=on}} across at 440 thousand years, and for asteroids {{convert|5|km|mi|abbr=on}} across at 18 million years.<ref name="Earth-impact"/> Some other models estimate similar impact frequencies,<ref name="MorbidelliAstIII"/> while others calculate higher frequencies.<ref name="Asher2005"/> For Tunguska-sized (10 megaton) impacts, the estimates range from one event every 2,000–3,000 years to one event every 300 years.<ref name="Asher2005"/>

{{wide image|SmallAsteroidImpacts-Frequency-Bolide-20141114.jpg|600px|align-cap=center|Location and impact energy of small asteroids impacting Earth's atmosphere}}

The second-largest observed event after the Tunguska meteor was a 1.1 megaton air blast in 1963 near the [[Prince Edward Islands]] between South Africa and Antarctica. However, this event was detected only by [[infrasound]] sensors,<ref name="David_spacecom"/><ref name=silber>{{cite journal |first1=Elizabeth A. |last1=Silber |first2=Douglas O. |last2=Revelle |first3=Peter G. |last3=Brown |first4=Wayne N. |last4=Edwards |title=An estimate of the terrestrial influx of large meteoroids from infrasonic measurements |journal=[[Journal of Geophysical Research]] |volume=114 |issue=E8 |year=2009 |article-number=2009JE003334 |doi=10.1029/2009JE003334 |doi-access=free |bibcode=2009JGRE..114.8006S}}</ref> which led to speculation that this may have been a [[nuclear test]].<ref name=Allen>{{cite journal |last1=Allen |first1=Robert S. |title=Antarctic Explosion Could Have Been Nuclear Detonation |journal=[[The San Bernardino Sun]] |issue=4 December |year=1963 |at=p. 40 col. f |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SBS19631204.1.40&e=-------en--20--1--txt-txIN--------1}}</ref> The third-largest, but by far best-observed impact, was the [[Chelyabinsk meteor]] of 15 February 2013. A previously unknown {{convert|20|m|ft|abbr=on}} asteroid exploded above this Russian city with an equivalent blast yield of 400–500 kilotons.<ref name="David_spacecom">{{cite news |first=Leonard |last=David |title=Russian fireball explosion shows meteor risk greater than thought |date=November 1, 2013 |work=Space.com |url=http://www.space.com/23423-russian-fireball-meteor-airburst-risk.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170819031019/https://www.space.com/23423-russian-fireball-meteor-airburst-risk.html |archive-date=August 19, 2017}}</ref> The calculated orbit of the pre-impact asteroid is similar to that of Apollo asteroid {{mpl|2011 EO|40}}, making the latter the meteor's possible parent body.<ref>{{cite journal |title=Reconstructing the Chelyabinsk event: Pre-impact orbital evolution |first1=C. |last1=de&nbsp;la&nbsp;Fuente Marcos |first2=R. |last2=de&nbsp;la&nbsp;Fuente Marcos |date=September 1, 2014 |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=443 |issue=1 |pages=L39–L43 |arxiv=1405.7202 |bibcode=2014MNRAS.443L..39D |doi=10.1093/mnrasl/slu078 |doi-access=free |s2cid=118417667}}</ref>

[[File:Sar2667 as it entered Earth's atmosphere over the north of France.jpg|thumb|Seven hours after discovery, {{mpl|2023 CX|1}} burns up as a meteor over northern France]]
On October 7, 2008, 20 hours after it was first observed and 11 hours after its trajectory has been calculated and announced, {{convert|4|m|ft|abbr=on}} asteroid {{mpl|2008 TC|3}} blew up {{convert|37|km|sigfig=2|abbr=on}} above the [[Nubian Desert]] in Sudan. It was the first time that an asteroid was observed and its impact was predicted prior to its entry into the atmosphere as a [[meteor]]. {{Convert|10.7|kg|lb|1}} of meteorites were recovered after the impact.<ref>{{cite journal |last1=Shaddad |first1=Muawia H. |display-authors=etal |title=The recovery of asteroid {{mp|2008 TC|3}} |journal=Meteoritics & Planetary Science |volume=45 |issue=10–11 |pages=1557–1589 |date=October 2010 |doi=10.1111/j.1945-5100.2010.01116.x |bibcode=2010M&PS...45.1557S |doi-access=free}}</ref> {{As of|2024|12}}, eleven impacts have been predicted, all of them small bodies that produced meteor explosions,<ref>{{Cite news |first=Brett |last=Tingley |title=Tiny asteroid detected hours before hitting Earth to become 4th 'imminent impactor' of 2024 |date=December 3, 2024 |work=Space.com |url=https://www.space.com/the-universe/asteroids/tiny-asteroid-detected-hours-before-hitting-earth-to-become-4th-imminent-impactor-of-2024 |access-date=December 31, 2024 |url-status=live |archive-url=https://web.archive.org/web/20241220093823/https://www.space.com/the-universe/asteroids/tiny-asteroid-detected-hours-before-hitting-earth-to-become-4th-imminent-impactor-of-2024 |archive-date=December 20, 2024}}</ref> with some impacts in remote areas only detected by the [[Comprehensive Nuclear-Test-Ban Treaty Organization]]'s [[Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization#International Monitoring System (IMS)|International Monitoring System (IMS)]], a network of infrasound sensors designed to detect the detonation of nuclear devices.<ref name="S&T140102">{{cite news |first1=Kelly |last1=Beatty |title=Small asteroid 2014&nbsp;AA hits Earth |magazine=[[Sky & Telescope]] |date=January 2, 2014 |url=http://www.skyandtelescope.com/astronomy-news/small-asteroid-2014-aa-hitsearth/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240725072341/https://skyandtelescope.org/astronomy-news/small-asteroid-2014-aa-hitsearth/ |archive-date=July 25, 2024}}</ref> [[Asteroid impact prediction]] remains in its infancy and successfully predicted asteroid impacts are rare. The vast majority of impacts recorded by IMS are not predicted.<ref>{{cite web |title=Fireballs. Fireball and Bolide Data |date=December 20, 2024 |publisher=NASA/JPL |url=http://cneos.jpl.nasa.gov/fireballs/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175038/http://cneos.jpl.nasa.gov/fireballs/ |archive-date=January 1, 2025}}</ref>

Observed impacts aren't restricted to the surface and atmosphere of Earth. Dust-sized NEOs have impacted man-made spacecraft, including the space probe [[Long Duration Exposure Facility]], which collected [[interplanetary dust cloud|interplanetary dust]] in low Earth orbit for six years from 1984.<ref name="Rubin2010"/> Impacts on the Moon can be observed as flashes of light with a typical duration of a fraction of a second.<ref name="NASA-lunar-impacts"/> The first lunar impacts were recorded during the 1999 Leonid storm.<ref>{{cite encyclopedia |last1=Rubio |first1=Luis R. Bellot |last2=Ortiz |first2=Jose L. |last3=Sada |first3=Pedro V. |title=Observation and Interpretation of Meteoroid Impact Flashes on the Moon |editor1-last=Jenniskens |editor1-first=P. |editor2-last=Rietmeijer |editor2-first=F. |editor3-last=Brosch |editor3-first=N. |editor4-last=Fonda |editor4-first=M. |display-editors=1 |encyclopedia=Leonid Storm Research |publisher=Springer |location=Dordrecht |year=2000 |pages=575–598 |isbn=978-90-481-5624-5 |doi=10.1007/978-94-017-2071-7_42 |bibcode=2000lsr..book..575B |s2cid=118392496}}</ref> Subsequently, several continuous monitoring programs were launched.<ref name="NASA-lunar-impacts">{{cite web |title=Lunar Impact Monitoring Program |publisher=NASA |url=https://www.nasa.gov/meteoroid-environment-office/about-lunar-impact-monitoring/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240127144250/https://www.nasa.gov/meteoroid-environment-office/about-lunar-impact-monitoring/ |archive-date=January 27, 2024}}</ref><ref name="2013-lunar-impact"/><ref name="ESA-lunar-impacts">{{cite web |title=About the NELIOTA project |publisher=ESA |url=https://neliota.astro.noa.gr/About/Project |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240307162344/https://neliota.astro.noa.gr/About/Project?AspxAutoDetectCookieSupport=1 |archive-date=March 7, 2024}}</ref> A lunar impact that was observed on September 11, 2013, lasted 8 seconds, was likely caused by an object {{convert|0.6–1.4|m|ft|abbr=on}} in diameter,<ref name="2013-lunar-impact">{{cite news |first=Michele |last=Catanzaro |title=Largest lunar impact caught by astronomers |date=February 24, 2014 |journal=Nature |url=https://www.nature.com/articles/nature.2014.14773 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20211004133116/https://www.nature.com/articles/nature.2014.14773 |archive-date=October 4, 2021}}</ref> and created a new crater {{convert|40|m|ft|abbr=on}} across, was the largest ever observed {{as of|lc=y|2019|07}}.<ref>{{cite web |title=MIDAS: Moon Impacts Detection and Analysis System. Main Results |work=Meteoroides.NET |url=http://www.meteoroides.net/e_midas_results.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240307162029/http://www.meteoroides.net/e_midas_results.html |archive-date=March 7, 2024}}</ref>

=== Risk ===
{{see also|Asteroid impact prediction}}
[[File:Toutatis.jpg|thumb|Asteroid [[4179 Toutatis]], a [[potentially hazardous object]] that passed within 4 [[lunar distance (astronomy)|lunar distances]] in September 2004 and currently has a minimum possible distance of 2.5 lunar distances]]

Through human history, the [[risk]] that any near-Earth object poses has been viewed having regard to both the [[culture]] and the [[technology]] of [[human society]]. Through history, humans have associated NEOs with changing risks, based on religious, philosophical or scientific views, as well as humanity's technological or economical capability to deal with such risks.<ref name="tsr20120514">
{{cite journal |first=Luis |last=Fernández Carril |title=The evolution of near Earth objects risk perception |journal=[[The Space Review]] |date=May 14, 2012 |url=http://www.thespacereview.com/article/2080/1 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170629205156/http://www.thespacereview.com/article/2080/1 |archive-date=June 29, 2017}}</ref> Thus, NEOs have been seen as [[omen]]s of natural disasters or wars; harmless spectacles in an unchanging universe; the source of era-changing cataclysms<ref name="tsr20120514"/> or potentially poisonous fumes (during Earth's passage through the tail of Halley's Comet in 1910);<ref>{{cite news |first=Stuart |last=Clark |title=Apocalypse postponed: how Earth survived Halley's comet in 1910 |date=December 20, 2012 |work=[[The Guardian]] |url=https://www.theguardian.com/science/across-the-universe/2012/dec/20/apocalypse-postponed-halley-comet |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171222021944/https://www.theguardian.com/science/across-the-universe/2012/dec/20/apocalypse-postponed-halley-comet |archive-date=December 22, 2017}}</ref> and finally as a possible cause of a crater-forming impact that could even cause [[extinction]] of humans and other life on Earth.<ref name="tsr20120514"/>

The potential of catastrophic impacts by near-Earth comets was recognised as soon as the first orbit calculations provided an understanding of their orbits: in 1694, Edmond Halley presented a theory that [[Genesis flood narrative|Noah's flood]] in the [[Bible]] was caused by a comet impact.<ref>{{cite web |first=Jason |last=Colavito |title=Noah's Comet. Edmond Halley 1694 |work=Jasoncolavito.com |url=http://www.jasoncolavito.com/halley-on-noahs-comet.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171001192755/http://www.jasoncolavito.com/halley-on-noahs-comet.html |archive-date=October 1, 2017}}</ref>

Human [[perception]] of near-Earth asteroids as benign objects of fascination or killer objects with high risk to [[human society]] has ebbed and flowed during the short time that NEAs have been scientifically observed.<ref name="wired20130323">{{cite news |first=David S. |last=Portree |title=Earth-Approaching Asteroids as Targets for Exploration (1978) |magazine=[[Wired (magazine)|Wired]] |date=March 23, 2013 |quote=People in the early 21st century have been encouraged to see asteroids as the interplanetary equivalent of sea monsters. We often hear talk of "killer asteroids," when in fact there exists no conclusive evidence that any asteroid has killed anyone in all of human history. ... In the 1970s, asteroids had yet to gain their present fearsome reputation ... most astronomers and planetary scientists who made a career of studying asteroids rightfully saw them as sources of fascination, not of worry. |url=https://www.wired.com/2013/03/earth-approaching-asteroids-as-targets-for-exploration-1978/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240601020647/https://www.wired.com/2013/03/earth-approaching-asteroids-as-targets-for-exploration-1978/ |archive-date=June 1, 2024}}</ref> The 1937 close approach of Hermes and the 1968 close approach of Icarus first raised impact concerns among scientists. Icarus earned significant public attention due to alarmist news reports, while Hermes was considered a threat because it was lost after its discovery; thus its orbit and potential for collision with Earth were not known precisely.<ref name="Marsden1998"/> Hermes was only re-discovered in 2003, and it is now known to be no threat for at least the next century.<ref name="RadarHermes"/>

Scientists have recognised the threat of impacts that create craters much bigger than the impacting bodies and have indirect effects on an even wider area since the 1980s, with mounting evidence for the theory that the [[Cretaceous–Paleogene extinction event]] (in which the non-avian dinosaurs died out) 65 million years ago was caused by a [[Chicxulub crater|large asteroid impact]].<ref name="tsr20120514"/><ref name="Chapman1998">{{cite web |first=Clark R. |last=Chapman |title=History of The Asteroid/Comet Impact Hazard |date=October 7, 1998 |publisher=Southwest Research Institute |url=http://www.boulder.swri.edu/clark/ncarhist.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203022823/https://www.boulder.swri.edu/clark/ncarhist.html |archive-date=December 3, 2024}}</ref> On March 23, 1989, the {{convert|300|m|ft|abbr=on}} diameter Apollo asteroid [[4581 Asclepius]] (1989 FC) missed the Earth by {{convert|700,000|km|mi|abbr=on}}. If the asteroid had impacted it would have created the largest explosion in recorded history, equivalent to 20,000 [[TNT equivalent|megatons of TNT]]. It attracted widespread attention because it was discovered only after the closest approach.<ref>{{cite news |first=Warren E. |last=Leary |title=Big Asteroid Passes Near Earth Unseen In a Rare Close Call |date=April 20, 1989 |work=[[The New York Times]] |url=https://www.nytimes.com/1989/04/20/us/big-asteroid-passes-near-earth-unseen-in-a-rare-close-call.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171109191344/http://www.nytimes.com/1989/04/20/us/big-asteroid-passes-near-earth-unseen-in-a-rare-close-call.html |archive-date=November 9, 2017}}</ref>

From the 1990s, a typical frame of reference in searches for NEOs has been the scientific concept of [[risk]]. The awareness of the wider public of the impact risk rose after the observation of the impact of the fragments of [[Comet Shoemaker–Levy 9]] into Jupiter in July 1994.<ref name="tsr20120514"/><ref name="Chapman1998"/> In March 1998, early orbit calculations for recently discovered asteroid {{mpl|(35396) 1997 XF|11}} showed a potential 2028 close approach {{convert |0.00031 |AU |km |abbr=on |lk=off}} from the Earth, well within the orbit of the Moon, but with a large error margin allowing for a direct hit. Further data allowed a revision of the 2028 approach distance to {{convert |0.0064 |AU |km |abbr=on |lk=off}}, with no chance of collision. By that time, inaccurate reports of a potential impact had caused a media storm.<ref name="Marsden1998">{{cite news |first=Brian G. |last=Marsden |author-link=Brian G. Marsden |title=How the Asteroid Story Hit: An Astronomer Reveals How a Discovery Spun Out of Control |date=March 29, 1998 |work=[[The Boston Globe]] |url=http://www.minorplanetcenter.net/iau/pressinfo/1997XF11Globe.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20120617210302/http://www.minorplanetcenter.net/iau/pressinfo/1997XF11Globe.html |archive-date=June 17, 2012}}</ref>

In 1998, the movies ''[[Deep Impact (film)|Deep Impact]]'' and ''[[Armageddon (1998 film)|Armageddon]]'' popularised the notion that near-Earth objects could cause catastrophic impacts.<ref name="Chapman1998"/> Also at that time, a [[conspiracy theory]] arose about a supposed 2003 impact of a planet called [[Nibiru cataclysm|Nibiru]] with Earth, which persisted on the internet as the predicted impact date was moved to 2012 and then 2017.<ref name="Molloy2017">{{cite news |first=Mark |last=Molloy |title=Nibiru: How the nonsense Planet X Armageddon and Nasa fake news theories spread globally |date=September 24, 2017 |work=[[The Daily Telegraph]] |url=https://www.telegraph.co.uk/news/2017/09/21/nibiru-nonsense-planet-x-armageddon-nasa-fake-news-theories/ |access-date=January 2, 2025 |url-status=live |url-access=subscription |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/2017/09/21/nibiru-nonsense-planet-x-armageddon-nasa-fake-news-theories/ |archive-date=January 11, 2022}}{{cbignore}}</ref>

==== Risk scales ====

There are two schemes for the scientific classification of impact hazards from NEOs, as a way to communicate the risk of impacts to the general public.
[[Image:Torino scale.svg|right|thumb|300px|The [[Torino scale]]. The scale in metres is the approximate diameter of an asteroid with a typical collision velocity]]
The simple [[Torino scale]] was established at an IAU workshop in [[Turin]] ({{langx|it|Torino}}) in June 1999, in the wake of the public confusion about the impact risk of {{mpl|1997 XF|11}}.<ref name="NEO-IAU">{{cite conference |first=Hans |last=Rickman |date=2001 |title=NEO Research and the IAU |pages=97–102 |conference=International Workshop on Collaboration and Coordination among NEO Observers and Orbital Computers |location=Kurshiki City Art Museum, Japan |publisher=IAU |editor-first1=Syuzo |editor-last1=Isobe |editor-first2=Yoshifusa |editor-last2=Asakuro |bibcode=2001ccno.conf...97R}}</ref> It rates the risks of impacts in the next 100 years according to impact energy and impact probability, using integer numbers between 0 and 10:<ref name="torino">{{cite web |title=Torino Impact Hazard Scale |publisher=NASA/JPL CNEOS |url=http://cneos.jpl.nasa.gov/sentry/torino_scale.html |access-date=February 14, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250214111538/https://cneos.jpl.nasa.gov/sentry/torino_scale.html |archive-date=February 14, 2025}}</ref><ref>{{cite journal |title=Torino Impact Hazard Scale |journal=Planetary and Space Science |volume=48 |issue=4 |pages=297–303 |bibcode=2000P&SS...48..297B |last1=Binzel |first1=Richard P. |year=2000 |doi=10.1016/S0032-0633(00)00006-4}}</ref>
* ratings of 0 and 1 are of no concern to astronomers or the public,
* ratings of 2 to 4 are used for events with increasing magnitude of concern to astronomers trying to make more precise orbit calculations, but not yet a concern for the public,
* ratings of 5 to 7 are meant for impacts of increasing magnitude which are not certain but warrant public concern and governmental contingency planning over an increasing timescale,
* 8 to 10 would be used for certain collisions of increasing severity.

The more complex [[Palermo scale]], established in 2002, compares the likelihood of an impact at a certain date to the probable number of impacts of a similar energy or greater until the possible impact, and takes the [[logarithm]] of this ratio. Thus, a Palermo scale rating can be any positive or negative real number, and risks of any concern are indicated by values above zero. Unlike the Torino scale, the Palermo scale is not sensitive to newly discovered small objects with an orbit known with low confidence.<ref name="palermo">{{cite web |title=Palermo Technical Impact Hazard Scale |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/sentry/palermo_scale.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231001191140/https://cneos.jpl.nasa.gov/sentry/palermo_scale.html |archive-date=October 1, 2023}}</ref>

==== Highly rated risks ====
The National Aeronautics and Space Administration [[NASA]] maintains an automated system to evaluate the threat from known NEOs over the next 100 years, which generates the continuously updated [[Sentry Risk Table]].<ref name="Current_Impact_Risks" /> All or nearly all of the objects are highly likely to drop off the list eventually as more observations come in, reducing the uncertainties and enabling more accurate orbital predictions.<ref name="Current_Impact_Risks"/><ref name="2006HZ51">{{cite news |first=David |last=Chandler |title=Big new asteroid has slim chance of hitting Earth |date=May 2, 2006 |work=New Scientist |url=https://www.newscientist.com/article/dn9095-big-new-asteroid-has-slim-chance-of-hitting-earth |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241226121230/https://www.newscientist.com/article/dn9095-big-new-asteroid-has-slim-chance-of-hitting-earth/ |archive-date=December 26, 2024}}</ref> When the close approach of a newly discovered asteroid is first put on a risk list with a significant risk, it is normal for the risk to first increase, regardless of whether the potential impact will eventually be ruled out or confirmed with the help of additional observations.<ref name="Smithsonian_no-panic">{{Cite news |first=Margherita |last=Bassi |title=Astronomers Raise Odds of Asteroid Impact in 2032 to 2.3 Percent—Here's Why You Shouldn't Panic |date=February 6, 2025 |work=[[Smithsonian (magazine)|Smithsonian]] |url=https://www.smithsonianmag.com/smart-news/astronomers-raise-odds-of-asteroid-impact-in-2032-to-2-3-percent-heres-why-you-shouldnt-panic-180985949/ |access-date=February 8, 2025 |url-status=live |archive-url=https://archive.today/20250208215442/https://www.smithsonianmag.com/smart-news/astronomers-raise-odds-of-asteroid-impact-in-2032-to-2-3-percent-heres-why-you-shouldnt-panic-180985949/ |archive-date=February 8, 2025}}</ref> Similar tables are maintained by the [[Near-Earth Object Coordination Centre]] (NEOCC) of the [[European Space Agency]] (ESA)<ref name="NEOCC-risk-list">{{cite web |title=Risk List |publisher=ESA NEOCC |url=https://neo.ssa.esa.int/risk-list |access-date=February 9, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250207044752/https://neo.ssa.esa.int/risk-list |archive-date=February 7, 2025}}</ref> and on the [[NEODyS]] (Near Earth Objects Dynamic Site) by the [[University of Pisa]] spin-off company SpaceDyS.<ref>{{cite web |title=NEODyS-2 Risk List |website=NEODyS-2 |publisher=ESA |url=https://newton.spacedys.com/neodys/index.php?pc=4.1 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250102113021/https://newton.spacedys.com/neodys/index.php?pc=4.1 |archive-date=January 2, 2025}}</ref>

In March 2002, {{mpl|(163132) 2002 CU|11}} became the first asteroid with a temporarily positive rating on the Torino Scale, with about a 1 in 9,300 chance of an impact in 2049.<ref>{{cite news |first1=Andrea |last1=Milani |first2=Giovanni |last2=Valsecchi |first3=Maria Eugenia |last3=Sansaturio |title=The problem with 2002 CU11 |work=Tumbling Stone |volume=12 |publisher=[[NEODyS]] |date=March 12, 2002 |url=http://spaceguard.rm.iasf.cnr.it/tumblingstone/issues/num12/eng/2002cu11.htm |access-date=January 29, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20160304023838/http://spaceguard.rm.iasf.cnr.it/tumblingstone/issues/num12/eng/2002cu11.htm |archive-date=March 4, 2016}}</ref> Additional observations reduced the estimated risk to zero, and the asteroid was removed from the Sentry Risk Table in April 2002.<ref name="removed">{{cite web |title=Date/Time Removed |date=December 31, 2024 |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/sentry/removed.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175144/https://cneos.jpl.nasa.gov/sentry/removed.html |archive-date=January 1, 2025}}</ref> It is now known that within the next two centuries, {{mp|2002 CU|11}} will pass the Earth at a safe closest distance (perigee) of {{convert|0.00425|AU|km mi|abbr=on|lk=off}} on August 31, 2080.<ref>{{cite web |title=Small-Body Database Lookup. 163132 (2002 CU11) |date=June 6, 2022 |publisher=NASA/JPL |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2002CU11&view=OPC |access-date=January 2, 2025}}</ref>

[[File:1950 DA (color).png|thumb|Radar image of asteroid {{mpl|29075|1950 DA}}]]
Asteroid {{mpl|29075|1950 DA}} has a diameter of about a kilometer (0.6 miles), and an impact would therefore be globally catastrophic. Although this asteroid will not strike for at least 800 years and thus has no Torino scale rating, it was added to the Sentry list in April 2002 as the first object with a Palermo scale value greater than zero.<ref name="IAU-NEOs"/><ref name="NEO-1950DA">{{cite web |title=29075 (1950 DA) Analyses, 2001-2007 |publisher=NASA/JPL CNEOS |url=http://cneos.jpl.nasa.gov/doc/1950da/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241228030108/https://cneos.jpl.nasa.gov/doc/1950da/ |archive-date=December 28, 2024}}</ref> The then-calculated 1 in 300 maximum chance of impact and +0.17 Palermo scale value was roughly 50% greater than the background risk of impact by all similarly large objects until 2880.<ref name="NEO-1950DA"/><ref>{{cite journal |last1=Giorgini |first1=J. D. |last2=Ostro |first2=S. J. |last3=Benner |first3=L. A. M. |last4=Chodas |first4=P. W. |last5=Chesley |first5=S. R. |last6=Hudson |first6=R. S. |last7=Nolan |first7=M. C. |last8=Klemola |first8=A. R. |last9=Standish |first9=E. M. |last10=Jurgens |first10=R. F. |last11=Rose |first11=R |last12=Chamberlin |first12=A. B. |last13=Yeomans |first13=D. K. |last14=Margot |first14=J. L. |display-authors=2 |date=April 5, 2002 |title=Asteroid 1950 DA's Encounter with Earth in 2880: Physical Limits of Collision Probability Prediction |journal=Science |volume=296 |pages=132–136 |url=https://cneos.jpl.nasa.gov/doc/1950da/1950da_published.pdf |access-date=January 26, 2024 |url-status=live |archive-url=https://web.archive.org/web/20241222123826/https://cneos.jpl.nasa.gov/doc/1950da/1950da_published.pdf |archive-date=December 22, 2024 |doi=10.1126/science.1068191 |pmid=11935024 |issue=5565|bibcode = 2002Sci...296..132G |s2cid=8689246}}</ref> After additional radar<ref name=Farnocchia2013>{{Cite journal |last1=Farnocchia |first1=Davide |last2=Chesley |first2=Steven R. |title=Assessment of the 2880 impact threat from asteroid (29075) 1950 DA |date=2013 |journal=Icarus |volume=229 |pages=321–327 |arxiv=1310.0861 |doi=10.1016/j.icarus.2013.09.022 |bibcode=2014Icar..229..321F |s2cid=56453734}}</ref> and optical observations, {{As of|2025|3|lc=y}}, the probability of this impact is assessed at 1 in 2,600.<ref name="Current_Impact_Risks"/> The corresponding Palermo scale value of −0.92 is the second-highest for all objects on the Sentry List Table.<ref name="Current_Impact_Risks"/>

On December 24, 2004, five days after discovery, {{convert|370|m|ft|abbr=on}} asteroid [[99942 Apophis]] was assigned a 4 on the Torino scale, the highest rating given to date, as the information available at the time translated to a 1.6% chance of Earth impact in April 2029.<ref>{{cite news |first1=D. |last1=Yeomans |first2=S. |last2=Chesley |first3=P. |last3=Chodas |title=Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale |date=December 23, 2004 |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news146.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241231201857/https://cneos.jpl.nasa.gov/news/news146.html |archive-date=December 31, 2024}} <small>(Note: at the time the object was yet unnamed and was known only by its provisional designation {{mp|2004 MN|4}}.)</small></ref> As observations were collected over the next three days, the calculated chance of impact first increased to as high as 2.7%,<ref name="cneosnews164">{{cite news |first1=Dwayne |last1=Brown |first2=DC |last2=Agle |title=NASA Refines Asteroid Apophis' Path Toward Earth |date=October 7, 2009 |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news164.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241218203929/https://cneos.jpl.nasa.gov/news/news164.html |archive-date=December 18, 2024}}</ref> then fell back to zero, as the shrinking uncertainty zone for this close approach no longer included the Earth.<ref>{{cite news |first1=D. |last1=Yeomans |first2=S. |last2=Chesley |first3=P. |last3=Chodas |title=Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4 |date=December 27, 2004 |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news148.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241230120623/https://cneos.jpl.nasa.gov/news/news148.html |archive-date=December 30, 2024}}</ref> There was at that time still some uncertainty about potential impacts during later close approaches. However, as the precision of orbital calculations improved due to additional observations, the risk of impact at any date was eliminated<ref>{{cite news |title=NASA Analysis: Earth Is Safe From Asteroid Apophis for 100-Plus Years |date=March 25, 2021 |work=News |publisher=NASA/JPL |url=https://www.jpl.nasa.gov/news/nasa-analysis-earth-is-safe-from-asteroid-apophis-for-100-plus-years |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241212054436/https://www.jpl.nasa.gov/news/nasa-analysis-earth-is-safe-from-asteroid-apophis-for-100-plus-years/ |archive-date=December 12, 2024}}</ref> and Apophis was removed from the Sentry Risk Table in February 2021.<ref name="removed"/>

{{As of|2025|3}}, {{mpl|2010 RF|12}} was listed on the Sentry List Table with the highest chance of impacting Earth, at 1 in 10 on September 5, 2095.<ref name="Current_Impact_Risks"/> At only {{convert|7|m|ft|abbr=on}} across, the asteroid however is much too small to be considered a [[potentially hazardous asteroid]] and it poses no serious threat: the possible 2095 impact therefore rates only −2.97 on the Palermo Scale.<ref name="Current_Impact_Risks"/>

In January 2025, {{convert|55|m|ft|abbr=on}} asteroid {{mpl|2024 YR|4}} reached a 3 rating on the Torino scale for a possible impact on December 22, 2032, triggering an action plan to schedule observations with more powerful telescopes as the object recedes and gets dimmer, to determine its orbit with more precision and thus refine the impact risk prediction.<ref>{{cite news |first=Ian |last=Sample |title=Asteroid triggers global defence plan amid chance of collision with Earth in 2032 |date=January 30, 2025 |work=The Guardian |url=https://www.theguardian.com/science/2025/jan/30/asteroid-spotted-chance-colliding-with-earth-2032 |access-date=February 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250202133421/https://www.theguardian.com/science/2025/jan/30/asteroid-spotted-chance-colliding-with-earth-2032 |archive-date=February 2, 2025}}</ref> In February 2025, the impact risk peaked at 1 in 32, then dropped below 1 in 1000 and the Torino scale rating was reduced to 0.<ref>{{cite news |first=Robert |last=Lea |title='That's impact probability zero folks!' Earth safe from 'city-killer' asteroid 2024 YR4 |date=February 24, 2025 |work=Space.com |url=https://www.space.com/the-universe/asteroids/earth-safe-from-city-killer-asteroid-2024-yr4-thats-impact-probability-zero-folks |access-date=March 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250302170948/https://www.space.com/the-universe/asteroids/earth-safe-from-city-killer-asteroid-2024-yr4-thats-impact-probability-zero-folks |archive-date=March 2, 2025}}</ref> {{As of|2025|3|2}}, the impact risk for the 2032 encounter was down to 1 in 120,000.<ref name="Current_Impact_Risks"/>  By April, {{mp|2024 YR|4}} was on the other hand estimated to have a 4% chance of impacting a 70% [[Lunar phase#waninggibbous|waning gibbous moon]] on 22 December 2032<ref name="Helsinki"/> around 15:17 to 15:21&nbsp;UTC.<ref name="BillGray"/>

=== Projects to minimize the threat ===
{{main|Asteroid impact avoidance}}

{{multiple image
 |direction = vertical
 |align     = right
 |width1    = 350
 |width2    = 350
 |image1    = NEA by survey.svg<!-- The Wikimedia file, which is from the "neo-jpl-stats" source, should be updated (overwritten) annually, using the end-of-the-year version saved from the source at the start of the next year, simultaneously with the other three files & the stats in this article from the "neo-jpl-stats" source -->
 |image2    = NEA 1 km or more.svg<!-- The Wikimedia file, which is from the "neo-jpl-stats" source, should be updated (overwritten) annually, using the end-of-the-year version saved from the source at the start of the next year, simultaneously with the other three files & the stats in this article from the "neo-jpl-stats" source -->
 |footer    = Annual NEA discoveries by survey: all NEAs (''top'') and NEAs &gt; 1&nbsp;km (''bottom'')
}}
A year before the 1968 close approach of asteroid Icarus, [[Massachusetts Institute of Technology]] students launched Project Icarus, devising a plan to deflect the asteroid with rockets in case it was found to be on a collision course with Earth.<ref>{{cite news |first=Dwayne A. |last=Day |title=Giant bombs on giant rockets: Project Icarus |date=July 5, 2004 |work=The Space Review |url=http://www.thespacereview.com/article/175/1 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20160415041026/http://www.thespacereview.com/article/175/1 |archive-date=April 15, 2016}}</ref> Project Icarus received wide media coverage, and inspired the 1979 disaster movie ''[[Meteor (film)|Meteor]]'', in which the US and the USSR join forces to blow up an Earth-bound fragment of an asteroid hit by a comet.<ref>{{cite news |title=MIT Course precept for movie |date=October 30, 1979 |work=[[The Tech (newspaper)|The Tech]] |publisher=MIT |url=http://tech.mit.edu/V99/PDF/V99-N43.pdf |access-date=November 15, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20140811005933/http://tech.mit.edu/V99/PDF/V99-N43.pdf |archive-date=August 11, 2014}}</ref>

The first astronomical program dedicated to the discovery of near-Earth asteroids was the [[Palomar Planet-Crossing Asteroid Survey]]. The link to impact hazard, the need for dedicated survey telescopes and options to head off an eventual impact were first discussed at a 1981 [[interdisciplinary]] conference in [[Snowmass, Colorado]].<ref name="Chapman1998"/> Plans for a more comprehensive survey, named the Spaceguard Survey, were developed by NASA from 1992, under a mandate from the [[United States Congress]].<ref name="Vulcano1995"/><ref name="spaceguard-1998" /> To promote the survey on an international level, the International Astronomical Union (IAU) organised a workshop at [[Vulcano]], Italy in 1995,<ref name="Vulcano1995">{{cite conference |author=<!--Staff writer(s); no by-line.--> |title=Vulcano Workshop. Beginning the Spaceguard Survey |location=Vulcano, Italy |publisher=IAU |date=September 1995 |url=http://spaceguard.rm.iasf.cnr.it/SGF/Vulcano/booklet.ps |access-date=March 13, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20131031042442/http://spaceguard.rm.iasf.cnr.it/SGF/Vulcano/booklet.ps |archive-date=October 31, 2013}}</ref> and set up [[The Spaceguard Foundation]] also in Italy a year later.<ref name="spaceguard-2004" /> In 1998, the [[United States Congress]] gave NASA a mandate to detect 90% of near-Earth asteroids over {{convert|1|km|mi|abbr=on}} diameter (that threaten global devastation) by 2008.<ref name="spaceguard-1998">{{cite web |first=Clark R. |last=Chapman |title=Statement on The Threat of Impact by Near-Earth Asteroids before the Subcommittee on Space and Aeronautics of the Committee on Science of the U.S. House of Representatives at its hearings on "Asteroids: Perils and Opportunities" |date=May 21, 1998 |publisher=Southwest Research Institute |url=http://www.boulder.swri.edu/clark/hr.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241206153404/https://www.boulder.swri.edu/clark/hr.html |archive-date=December 6, 2024}}</ref><ref name="shigad" />
[[File:PIA22419-Neowise-1stFourYearsDataFromDec2013-20180420.gif|thumb|300px|{{center|Asteroids discovered in the first three years of the [[Wide-field Infrared Survey Explorer#NEOWISE (pre-hibernation)|Near-Earth Object WISE]] program, starting in December 2013, with green dots showing NEAs}}]]
Several [[astronomical surveys|surveys]] have undertaken "[[Spaceguard]]" activities (an umbrella term), including [[Lincoln Near-Earth Asteroid Research]] (LINEAR), [[Spacewatch]], [[Near-Earth Asteroid Tracking]] (NEAT), [[Lowell Observatory Near-Earth-Object Search]] (LONEOS), [[Catalina Sky Survey]] (CSS), [[Campo Imperatore Near-Earth Object Survey]] (CINEOS), [[Japanese Spaceguard Association]], [[Asiago-DLR Asteroid Survey]] (ADAS) and [[Wide-field Infrared Survey Explorer#NEOWISE (pre-hibernation)|Near-Earth Object WISE]] (NEOWISE). As a result, the ratio of the known and the estimated total number of near-Earth asteroids larger than 1&nbsp;km in diameter rose from about 20% in 1998 to 65% in 2004,<ref name="spaceguard-2004">{{cite web |title=NASA on the Prowl for Near-Earth Objects |date=May 26, 2004 |publisher=NASA/JPL |url=https://www.nasa.gov/vision/universe/watchtheskies/near_earth052104.html |access-date=March 6, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20220813164957/https://www.nasa.gov/vision/universe/watchtheskies/near_earth052104.html |archive-date=August 13, 2022}}</ref> 80% in 2006,<ref name="shigad">{{cite news |last=Shiga |first=David |title=New telescope will hunt dangerous asteroids |date=June 27, 2006 |work=New Scientist |url=https://www.newscientist.com/article/dn9403-new-telescope-will-hunt-dangerous-asteroids/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203030816/https://www.newscientist.com/article/dn9403-new-telescope-will-hunt-dangerous-asteroids/ |archive-date=December 3, 2024}}</ref> and 93% in 2011. The original Spaceguard goal has thus been met, only three years late.<ref name="pia14734"/><ref name="WISE-asteroid-census"/> {{As of|2024|12}}, 867 NEAs larger than 1&nbsp;km have been discovered, of which one was discovered in 2024 and two in 2023.<ref name="neo-jpl-stats" />

In 2005, the original USA Spaceguard mandate was extended by the [[George E. Brown, Jr.]] Near-Earth Object Survey Act, which calls for NASA to detect 90% of NEOs with diameters of {{convert|140|m|ft|abbr=on}} or greater, by 2020.<ref name="law-109-155">{{cite web |title=Public Law 109–155–DEC.30, 2005 |url=http://www.govinfo.gov/content/pkg/PLAW-109publ155/pdf/PLAW-109publ155.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241206182016/https://www.govinfo.gov/content/pkg/PLAW-109publ155/pdf/PLAW-109publ155.pdf |archive-date=December 6, 2024}}</ref> In January 2016, NASA announced the creation of the [[Planetary Defense Coordination Office]] (PDCO) to coordinate an effective threat assessment, response and mitigation effort, which reinforced the goal to detect 90% of NEOs {{convert|140|m|ft|abbr=on}} or greater, but without a deadline.<ref name="ETech">{{cite news |first=Graham |last=Templeton |title=NASA is opening a new office for planetary defense |date=January 12, 2016 |work=[[ExtremeTech]] |url=http://www.extremetech.com/extreme/220745-nasa-is-opening-a-new-office-for-planetary-defense |access-date=March 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170706223602/https://www.extremetech.com/extreme/220745-nasa-is-opening-a-new-office-for-planetary-defense |archive-date=July 6, 2017}}</ref><ref>{{cite web |title=Planetary Defense Coordination Office. Overview |date=8 September 2023 |publisher=NASA |url=https://science.nasa.gov/planetary-defense-overview |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241226012441/https://science.nasa.gov/planetary-defense-overview/ |archive-date=December 26, 2024}}</ref> In September 2020, it was estimated that about half of these have been found, but objects of this size hit the Earth only about once in 30,000 years.<ref name="HarrisChodas2021">{{cite journal |first1=Alan W. |last1=Harris |first2=Paul W. |last2=Chodas |title=The population of near-earth asteroids revisited and updated |journal=Icarus |date=September 1, 2021 |volume=365 |at=section 114452 |article-number=114452 |doi=10.1016/j.icarus.2021.114452 |bibcode=2021Icar..36514452H|doi-access=free }}</ref><!-- 30,000 impact interval for d=140 m = H=22 can be read from Figure 15 in the article.--> In December 2023, using a lower absolute brightness estimate for smaller asteroids, the ratio of discovered NEOs with diameters of {{convert|140|m|ft|abbr=on}} or greater was estimated at 38%.<ref name="Grav2023"/><!-- This article uses a H=23 cutoff for d>140, but states that in H terms, the estimate is consistent withe the earlier one--> The Chile-based [[Vera C. Rubin Observatory]], which will survey the southern sky for transient events from 2025, is expected to increase the number of known asteroids by a factor of 10 to 100 and increase the ratio of known NEOs with diameters of {{convert|140|m|ft|abbr=on}} or greater to at least 60%,<ref>{{cite web |title=Science Goals. What's in our Solar System? |publisher=Vera C. Rubin Observatory |url=https://rubinobservatory.org/explore/science-goals/solar-system |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241219033206/https://rubinobservatory.org/explore/science-goals/solar-system |archive-date=December 19, 2024}}</ref> while the [[NEO Surveyor]] satellite, to be launched in 2027, is expected to push the ratio to 76% during its 5-year mission.<ref name="Grav2023">{{cite journal |last1=Grav |first1=Tommy |last2=Mainzer |first2=Amy K. |title=The NEO Surveyor Near-Earth Asteroid Known Object Model |journal=[[The Planetary Science Journal]] |volume=4 |issue=12 |at=part 228 |date=December 5, 2023 |doi=10.3847/PSJ/ad072e|doi-access=free |arxiv=2310.20149 |bibcode=2023PSJ.....4..228G}}</ref>

Survey programs aim to identify threats years in advance, giving humanity time to prepare a space mission to avert the threat.

{{blockquote|REP. STEWART: ... are we technologically capable of launching something that could intercept [an asteroid]? ...<br /> DR. A'HEARN: No. If we had spacecraft plans on the books already, that would take a year ... I mean a typical small mission ... takes four years from approval to start to launch ...|author=[[Chris Stewart (politician)|Rep. Chris Stewart (R, UT)]] and [[Michael A'Hearn|Dr. Michael F. A'Hearn]], April 10, 2013 |source=[[United States Congress]]<ref name="US-Congress-20130410">{{cite web |author=U.S.Congress |title=Threats From Space: a Review of U.S. Government Efforts to Track and mitigate Asteroids and Meteors (Part I and Part II) – Hearing Before the Committee on Science, Space, and Technology House of Representatives One Hundred Thirteenth Congress First Session |url=https://www.govinfo.gov/content/pkg/CHRG-113hhrg80552/pdf/CHRG-113hhrg80552.pdf |date=March 19, 2013 |page=147 |publisher=United States Congress |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241206150309/https://www.govinfo.gov/content/pkg/CHRG-113hhrg80552/pdf/CHRG-113hhrg80552.pdf |archive-date=December 6, 2024}}</ref>}}

The [[Asteroid Terrestrial-impact Last Alert System|ATLAS]] project, by contrast, aims to find impacting asteroids shortly before impact, much too late for deflection maneuvers but still in time to evacuate and otherwise prepare the affected Earth region.<ref>{{cite news |title=ATLAS: The Asteroid Terrestrial-impact Last Alert System |date=February 18, 2013 |work=[[Astronomy (magazine)|Astronomy]] |publisher=University of Hawaii at Mānoa Institute for Astronomy |url=https://www.astronomy.com/science/atlas-the-asteroid-terrestrial-impact-last-alert-system/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20230604015435/https://www.astronomy.com/science/atlas-the-asteroid-terrestrial-impact-last-alert-system/ |archive-date=June 4, 2023}}</ref> Another project, the [[Zwicky Transient Facility]] (ZTF), which surveys for objects that change their brightness rapidly,<ref name="AT-20180207">{{cite news |last=Kulkarni |first= S.R. |display-authors=etal |title=The Zwicky Transient Facility (ZTF) begins |url=http://www.astronomerstelegram.org/?read=11266 |date=February 7, 2018 |work=[[The Astronomer's Telegram]] |number=11266 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20180209062936/http://www.astronomerstelegram.org/?read=11266 |archive-date=February 9, 2018}}</ref> also detects asteroids passing close to Earth.<ref name="AT-20180208">{{cite news |last=Ye |first= Quan-Zhi|display-authors=etal|title=First Discovery of a Small Near Earth Asteroid with ZTF (2018 CL) |url=http://www.astronomerstelegram.org/?read=11274 |date=February 8, 2018 |work=The Astronomer's Telegram |number=11274 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20180209002703/http://www.astronomerstelegram.org/?read=11274 |archive-date=February 9, 2018}}</ref>

{{further|List of near-Earth object observation projects}}

Scientists involved in NEO research have also considered options for actively averting the threat if an object is found to be on a collision course with Earth.<ref name="Chapman1998"/> All viable methods aim to deflect rather than destroy the threatening NEO, because the fragments would still cause widespread destruction.<ref name="TaskForceReport"/> Deflection, which means a change in the object's orbit months to years prior to the [[Asteroid impact prediction|predicted impact]], also requires orders of magnitude less energy.<ref name="TaskForceReport"/>

== Number and classification ==
[[File:Known NEAs.svg|thumb|Cumulative discoveries of near-Earth asteroids known by size, 1980–{{#time:Y|-1 year}}|400px]]<!-- The Wikimedia file, which is from the "neo-jpl-stats" source, should be updated (overwritten) annually, using the end-of-the-year version saved from the source at the start of the next year, simultaneously with the other three files & the stats in this article from the "neo-jpl-stats" source -->

When an NEO is detected, like all other small Solar System bodies, its positions and brightness are submitted to the (IAU's) [[Minor Planet Center]] (MPC) for cataloging. The MPC maintains separate lists of confirmed NEOs and potential NEOs.<ref name="MPC-NEO-confirm">{{cite web |title=The NEO Confirmation Page |date=January 1, 2025 |publisher=IAU/MPC |url=http://www.minorplanetcenter.net/iau/NEO/toconfirm_tabular.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175114/http://www.minorplanetcenter.net/iau/NEO/toconfirm_tabular.html |archive-date=January 1, 2025}}</ref><ref>{{cite journal |last1=Marsden |first1=B. G. |last2=Williams |first2=G. V. |title=The NEO Confirmation Page |journal=[[Planetary and Space Science]] |volume=46 |issue=2 |pages=299 |bibcode=1998P&SS...46..299M |year=1998 |doi=10.1016/S0032-0633(96)00153-5}}</ref> The MPC maintains a separate list for the potentially hazardous asteroids (PHAs).<ref name="MPC-PHA-list">{{cite web |title=List Of Potentially Hazardous Minor Planets (by designation) |publisher=IAU/MPC |url=https://www.minorplanetcenter.net/iau/lists/t_phas.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250102134144/https://www.minorplanetcenter.net/iau/lists/t_phas.html |archive-date=January 2, 2025}}</ref> NEOs are also catalogued by two separate units of the [[Jet Propulsion Laboratory]] (JPL) of [[NASA]]: the [[Center for Near-Earth Object Studies]] (CNEOS)<ref name="neo-jpl-intro" /> and the Solar System Dynamics Group.<ref name="JPL-SSD-NEA"/> CNEOS's catalog of near-Earth objects includes the approach distances of asteroids and comets.<ref name="NEO-close">{{cite web |url=https://cneos.jpl.nasa.gov/ca/ |title=NEO Earth Close Approaches |date=January 2, 2025 |publisher=NASA/JPL CNEOS |access-date=January 1, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101175106/https://cneos.jpl.nasa.gov/ca/ |archive-date=January 1, 2025}}</ref> NEOs are also catalogued by a unit of [[European Space Agency|ESA]], the [[Near-Earth Object Coordination Centre]] (NEOCC).<ref name="NEOCC-about">{{cite web |title=About NEOCC |publisher=ESA NEOCC |url=https://neo.ssa.esa.int/about-neocc |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101040814/https://neo.ssa.esa.int/about-neocc |archive-date=January 1, 2025}}</ref>

Near-Earth objects are classified as [[meteoroid]]s, [[asteroid]]s, or [[comet]]s depending on size, composition, and orbit. Those which are asteroids can additionally be members of an [[asteroid family]], and comets create meteoroid streams that can generate [[meteor shower]]s.

{{As of|2024|12|30|df=US}} and according to statistics maintained by CNEOS, 37,378 NEOs have been discovered. Only 123 (0.33%) of them are comets, whilst 37,255 (99.67%) are asteroids. 2,465 of those NEOs are classified as potentially hazardous asteroids (PHAs).<ref name="neo-jpl-stats" />

{{As of|2025|2|2|df=US}}, 1,886 NEAs appear on the [[Sentry (monitoring system)|Sentry impact risk page]] at the [[NASA]] website.<ref name="Current_Impact_Risks"/> All but 106 of these NEAs are less than 50 meters in diameter, only one recently discovered object has an impact risk meriting a Torino Scale rating higher than zero, while none have a Palermo scale rating higher than zero.<ref name="torino"/>

=== Observational biases ===
The main problem with estimating the number of NEOs is that the probability of detecting one is influenced by a number of  aspects of the NEO, starting naturally with its size but also including the characteristics of its orbit and the reflectivity of its surface.<ref name="science.sciencemag.org">{{Cite journal |last1=Bottke |first1=W. F. Jr. |title=Understanding the Distribution of Near-Earth Asteroids |journal=Science |volume=288 |issue=5474 |pages=2190–2194 |year=2000 |pmid=10864864 |doi=10.1126/science.288.5474.2190 |bibcode=2000Sci...288.2190B}}</ref>  What is easily detected will be more counted, and these [[observational bias]]es need to be compensated when trying to calculate the number of bodies in a population from the list of its detected members.<ref name="science.sciencemag.org"/>
[[File:Artist%E2%80%99s_impression_of_an_asteroid_that_orbits_closer_to_the_Sun_than_Earth%E2%80%99s_orbit.jpg|thumb|right|Artist's impression of an asteroid that orbits closer to the Sun than Earth's orbit, showing its dark side]]

Bigger asteroids reflect more light, and the two biggest near-Earth objects, [[433 Eros]] and [[1036 Ganymed]], were naturally also among the first to be detected.<ref name="Browne">{{Cite news |first=Malcolm W. |last=Browne |title=Mathematicians Say Asteroid May Hit Earth in a Million Years |date=April 25, 1996 |work=The New York Times |url=https://www.nytimes.com/1996/04/25/us/mathematicians-say-asteroid-may-hit-earth-in-a-million-years.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241204111320/https://www.nytimes.com/1996/04/25/us/mathematicians-say-asteroid-may-hit-earth-in-a-million-years.html |archive-date=December 4, 2024}}</ref> 1036 Ganymed is about {{convert|35|km|mi|abbr=on}} in diameter and 433 Eros is about {{convert|17|km|mi|abbr=on}} in diameter.<ref name="Browne"/> Meanwhile, the apparent brightness of objects that are closer is higher, introducing a bias that favours the discovery of NEOs of a given size that get closer to Earth.<ref name="LuuJewitt1989"/>

Earth-based astronomy requires dark skies and hence nighttime observations, and even space-based telescopes avoid looking into directions close to the Sun, thus most NEO surveys are blind towards objects passing Earth on the side of the Sun.<ref name="LuuJewitt1989"/><ref name="NEOS-orbit"/> This bias is further enhanced by the effect of [[planetary phase|phase]]: the narrower the angle of the asteroid and the Sun from the observer, the lesser part of the observed side of the asteroid will be illuminated.<ref name="LuuJewitt1989"/> Another bias results from the different surface brightness or albedo of the objects, which can make a large but low-albedo object as bright as a small but high-albedo object.<ref name="LuuJewitt1989"/><ref name="NEOS-why-infrared"/> In addition, the reflexivity of asteroid surfaces is not uniform but increases towards the direction opposite of illumination, resulting in the phenomenon of phase darkening, which makes asteroids even brighter when the Earth is close to the axis of sunlight.<ref name="LuuJewitt1989"/> An asteroid's observed albedo usually has a strong peak or [[opposition surge]] very close to the direction opposite of the Sun.<ref name="LuuJewitt1989"/> Different surfaces display different levels of phase darkening, and research showed that, on top of albedo bias, this favours the discovery of silicon-rich [[S-type asteroid]]s over carbon-rich [[C-type asteroid|C types]], for example.<ref name="LuuJewitt1989">{{cite journal |first1=Jane |last1=Luu |first2=David |last2=Jewitt |title=On the Relative Numbers of C Types and S Types among Near-Earth Asteroids |journal=[[The Astronomical Journal]] |volume=98 |issue=5 |pages=1905–1911 |date=November 1989 |doi=10.1086/115267 |bibcode=1989AJ.....98.1905L}}</ref> As a result of these observational biases, in Earth-based surveys, NEOs tended to be discovered when they were in opposition, that is, opposite from the Sun when viewed from the Earth.<ref name="Grav2023"/>

The most practical way around many of these biases is to use [[thermal infrared]] telescopes in space that observe their thermal emissions instead of the visible light they reflect, with a sensitivity that is almost independent of the illumination.<ref name="Grav2023"/><ref name="NEOS-why-infrared">{{cite web |title=Why Infrared? |date=13 May 2024 |url=https://neos.epss.ucla.edu/index.php/2024/05/13/why-infared/ |publisher=UCLA |access-date=January 2, 2025}}</ref> In addition, space-based telescopes in an orbit around the Sun in the shadow of the Earth can make observations as close as 45 degrees to the direction of the Sun.<ref name="NEOS-orbit">{{cite web |title=Mission Orbit and Timeline |date=13 May 2024 |url=https://neos.epss.ucla.edu/index.php/2024/05/13/mission-orbit-and-timeline/ |publisher=UCLA |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250102153424/https://neos.epss.ucla.edu/index.php/2024/05/13/mission-orbit-and-timeline/ |archive-date=January 2, 2025}}</ref>

Further observational biases favour objects that have more frequent encounters with the Earth, which makes the detection of [[Aten asteroid|Atens]] more likely than that of [[Apollo asteroid|Apollos]]; and objects that move slower when encountering the Earth, which makes the detection of NEAs with low eccentricities more likely.<ref>{{cite journal |first1=William F. Jr. |last1=Bottke |first2=Michael C. |last2=Nolan |first3=H. Jay |last3=Melosh |first4=Ann M. |last4=Vickery |first5=Richard |last5=Greenberg |title=Origin of the Spacewatch Small Earth-Approaching Asteroids |journal=Icarus |date=August 1996 |volume=122 |issue=2 |pages=406–427 |url=https://www.boulder.swri.edu/~bottke/Reprints/Bottke_1996_Icarus_122_406_Origin_Spacewatch_NEOs.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241208013553/https://www.boulder.swri.edu/~bottke/Reprints/Bottke_1996_Icarus_122_406_Origin_Spacewatch_NEOs.pdf |archive-date=December 8, 2024 |doi=10.1006/icar.1996.0133 |bibcode=1996Icar..122..406B}}</ref>

Such observational biases must be identified and quantified to determine NEO populations, as studies of asteroid populations then take those known observational selection biases into account to make a more accurate assessment.<ref>{{cite journal |first1=B. |last1=Zellner |first2=E. |last2=Bowell |title=2. Asteroid Compositional Types and their Distributions |journal=International Astronomical Union Colloquium |year=1977 |volume=39 |pages=185–197 |doi=10.1017/S0252921100070093 |s2cid=128650102 |doi-access=free}}</ref> In the year 2000 and taking into account all known observational biases, it was estimated that there are approximately 900 near-Earth asteroids of at least kilometer size, or technically and more accurately, with an [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] brighter than 17.75.<ref name="science.sciencemag.org"/>

=== Near-Earth asteroids{{anchor|Near-Earth_asteroids}}<!--'Near-Earth asteroid' and 'Near-Earth asteroids' redirect here--> ===
[[File:ESO-Asteroid Toutatis-phot-28c-04-normal.jpg|thumb|One-minute path of asteroid [[4179 Toutatis]] in the sky during its September 2004 close approach ([[Paranal Observatory]])]]

These are asteroids in a near-Earth orbit without the tail or coma of a comet. {{As of|2024|12}}, 37,255 '''near-Earth asteroids'''<!--boldface per WP:R#PLA--> (NEAs) are known, 2,465 of which are both sufficiently large and may come sufficiently close to Earth to be classified as potentially hazardous.<ref name="neo-jpl-stats" />

NEAs survive in their orbits for just a few million years.<ref name="MorbidelliAstIII">{{cite book |first1=Alessandro |last1=Morbidelli |first2=William F. Jr. |last2=Bottke |first3=Christiane |last3=Froeschlé |first4=Patrick |last4=Michel |chapter=Origin and Evolution of Near-Earth Objects |editor-first1=W. F. |editor-last1=Bottke Jr. |editor-first2=A. |editor-last2=Cellino |editor-first3=P. |editor-last3=Paolicchi |editor-first4=R. P. |editor-last4=Binzel |display-editors=1 |title=Asteroids III |pages=409–422 |date=January 2002 |doi=10.2307/j.ctv1v7zdn4.33 |bibcode=2002aste.book..409M |url=http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |access-date=December 31, 2024 |url-status=live |archive-url=https://web.archive.org/web/20170809014123/http://www.boulder.swri.edu/%7Ebottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |archive-date=August 9, 2017}}</ref> They are eventually eliminated by planetary [[Perturbation (astronomy)|perturbations]], causing ejection from the Solar System or a [[Impact event|collision]] with the Sun, a planet, or other celestial body.<ref name="MorbidelliAstIII"/> With orbital lifetimes short compared to the age of the Solar System, new asteroids must be constantly moved into near-Earth orbits to explain the observed asteroids. The accepted origin of these asteroids is that [[Asteroid belt|main-belt asteroids]] are moved into the inner Solar System through [[orbital resonance]]s with [[Jupiter]].<ref name="MorbidelliAstIII"/> The interaction with Jupiter through the resonance [[Perturbation (astronomy)|perturb]]s the asteroid's orbit and it comes into the inner Solar System. The asteroid belt has gaps, known as [[Kirkwood gap]]s, where these resonances occur as the asteroids in these resonances have been moved onto other orbits. New asteroids migrate into these resonances, due to the [[Yarkovsky effect]] that provides a continuing supply of near-Earth asteroids.<ref>{{cite journal |title=The Yarkovsky-driven origin of near-Earth asteroids |first1=A. |last1=Morbidelli |first2=D. |last2=Vokrouhlický |journal=Icarus |volume=163 |issue=1 |pages=120–134 |date=May 2003 |doi=10.1016/S0019-1035(03)00047-2 |bibcode=2003Icar..163..120M |citeseerx=10.1.1.603.7624}}</ref> Compared to the entire mass of the asteroid belt, the mass loss necessary to sustain the NEA population is relatively small; totalling less than 6% over the past 3.5 billion years.<ref name="MorbidelliAstIII"/> The composition of near-Earth asteroids is comparable to that of asteroids from the asteroid belt, reflecting a variety of [[asteroid spectral types]].<ref>{{cite journal |title=On the Origins of Earth-Approaching Asteroids |first1=D.F. |last1=Lupishko |first2=T.A. |last2=Lupishko |name-list-style=amp |journal=[[Solar System Research]] |volume=35 |issue=3 |pages=227–233 |date=May 2001 |doi=10.1023/A:1010431023010 |bibcode = 2001SoSyR..35..227L|s2cid=117912062}}</ref>

A small number of NEAs are [[extinct comets]] that have lost their volatile surface materials, although having a faint or intermittent comet-like tail does not necessarily result in a classification as a near-Earth comet, making the boundaries somewhat fuzzy. The rest of the near-Earth asteroids are driven out of the asteroid belt by gravitational interactions with [[Jupiter]].<ref name = "MorbidelliAstIII" /><ref>{{cite journal |title=What the physical properties of near-Earth asteroids tell us about sources of their origin? |first1=D.F. |last1=Lupishko |first22=M. |last2=di Martino |first3=T.A. |last3=Lupishko |name-list-style=amp |journal=Kinematika I Fizika Nebesnykh Tel Supplimen |volume=3 |issue=3 |pages=213–216 |date=September 2000 |bibcode=2000KFNTS...3..213L}}</ref>

Many asteroids have [[natural satellite]]s ([[minor-planet moon]]s). {{As of|2024|12|df=US}}, 104 NEAs were known to have at least one moon, including five known to have two moons.<ref>{{cite web |title=Asteroids with Satellites |publisher=Johnston's Archive |date=December 28, 2024 |url=http://www.johnstonsarchive.net/astro/asteroidmoons.html |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250103104505/https://www.johnstonsarchive.net/astro/asteroidmoons.html |archive-date=January 3, 2025}}</ref> The asteroid [[3122 Florence]], one of the largest PHAs<ref name="MPC-PHA-list"/> with a diameter of {{convert|4.5|km|mi|abbr=on}}, has two moons measuring {{convert|100–300|m|ft|abbr=on}} across, which were discovered by radar imaging during the asteroid's 2017 approach to Earth.<ref name="Florence-moons">{{cite news |first1=Lance |last1=Benner |first2=Shantanu |last2=Naidu |first3=Marina |last3=Brozovic |first4=Paul |last4=Chodas |title=Radar Reveals Two Moons Orbiting Asteroid Florence |date=September 1, 2017 |work=News |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news199.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170903060914/https://cneos.jpl.nasa.gov/news/news199.html |archive-date=September 3, 2017}}</ref>

In May 2022, an algorithm known as Tracklet-less Heliocentric Orbit Recovery or THOR and developed by University of Washington researchers to discover asteroids in the solar system was announced as a success.<ref>{{Cite news |title=UW-developed, cloud-based astrodynamics platform to discover and track asteroids |date=May 31, 2022 |publisher=University of Washington |work=UW News |url=https://www.washington.edu/news/2022/05/31/asteroid-discovery/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203203327/https://www.washington.edu/news/2022/05/31/asteroid-discovery/ |archive-date=December 3, 2024}}</ref> The International Astronomical Union's Minor Planet Center confirmed a series of first candidate asteroids identified by the algorithm.<ref>{{Cite press release |title=Asteroid Institute Uses Revolutionary Cloud-Based Astrodynamics Platform to Discover and Track Asteroids |date=May 31, 2022 |publisher=B612 Foundation |work=PR Newswire |url=https://www.prnewswire.com/news-releases/asteroid-institute-uses-revolutionary-cloud-based-astrodynamics-platform-to-discover-and-track-asteroids-301557487.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241219010657/https://www.prnewswire.com/news-releases/asteroid-institute-uses-revolutionary-cloud-based-astrodynamics-platform-to-discover-and-track-asteroids-301557487.html |archive-date=December 19, 2024}}</ref>

==== Size distribution ====
[[File:NEA by size.svg|400px|thumb|Known near-Earth asteroids by size]]<!-- The Wikimedia file, which is from the "neo-jpl-stats" source, should be updated (overwritten) annually, using the end-of-the-year version saved from the source at the start of the next year, simultaneously with the other three files & the stats in this article from the "neo-jpl-stats" source -->

While the size of a very small fraction of these asteroids is known to better than 1%, from [[radar]] observations, from images of the asteroid surface, or from [[Occultation#Occultations by asteroids|stellar occultations]], the diameter of the vast majority of near-Earth asteroids has only been estimated on the basis of their brightness and a representative asteroid surface reflectivity or [[albedo]], which is commonly assumed to be 14%.<ref name="neo-jpl-intro">{{cite web |title=Discovery Statistics. Introduction |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/stats/ |date=2012 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240126214444/https://cneos.jpl.nasa.gov/stats/ |archive-date=January 26, 2024}}</ref> Such indirect size estimates are uncertain by over a factor of 2 for individual asteroids, since asteroid albedos can range at least as low as 5% and as high as 30%. This makes the volume of those asteroids uncertain by a factor of 8, and their mass by at least as much, since their assumed density also has its own uncertainty. Using this crude method, an [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] of 17.75 roughly corresponds to a diameter of {{convert|1|km|mi|abbr=on|lk=off}}<ref name="neo-jpl-intro"/> and an absolute magnitude of 22.0 to a diameter of {{convert|140|m|ft|abbr=on|lk=off}}.<ref name="CNEOS-NEO-groups"/>  Diameters of intermediate precision, better than from an assumed albedo but not nearly as precise as good direct measurements, can be obtained from the combination of reflected light and thermal infrared emission, using a thermal model of the asteroid to estimate both its diameter and its albedo. The reliability of this method, as applied by the [[Wide-field Infrared Survey Explorer]] and NEOWISE missions, has been the subject of a dispute between experts, with the 2018 publication of two independent analyses, one criticising and another giving results consistent with the WISE method.<ref name="NYT-20180614">{{cite news |last=Chang |first=Kenneth |title=Asteroids and Adversaries: Challenging What NASA Knows About Space Rocks |date=June 14, 2018 |work=The New York Times |url=https://www.nytimes.com/2018/06/14/science/asteroids-nasa-nathan-myhrvold.html |access-date=January 2, 2025 |url-access=subscription  |url-status=live |archive-url=https://web.archive.org/web/20241001084248/https://www.nytimes.com/2018/06/14/science/asteroids-nasa-nathan-myhrvold.html |archive-date=October 1, 2024}}{{cbignore}}</ref> A 2023 study re-evaluated the relationship of brightness, albedo and diameter. For many objects with a diameter larger than 1&nbsp;km, brightness estimates were reduced slightly. Meanwhile, based on new albedo estimates of smaller objects, the study found that {{nowrap|H {{=}} 23}} best corresponds to a diameter of 140&nbsp;m.<ref name="Grav2023"/>

In 2000, NASA reduced from 1,000–2,000 to 500–1,000 its estimate of the number of existing near-Earth asteroids over one kilometer in diameter, or more exactly brighter than an absolute magnitude of 17.75.<ref>{{cite news |first=Jane |last=Platt |title=Asteroid Population Count Slashed |date=January 12, 2000 |work=Press Releases |publisher=NASA/JPL |url=https://www.jpl.nasa.gov/news/asteroid-population-count-slashed |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240127123244/https://www.jpl.nasa.gov/news/asteroid-population-count-slashed |archive-date=January 27, 2024}}</ref><ref name="Rabinowitzetal00">{{cite journal |title=A reduced estimate of the number of kilometer-sized near-Earth asteroids |journal=Nature |first1=David |last1=Rabinowitz |first2=Eleanor |last2=Helin |first3=Kenneth |last3=Lawrence |first4=Steven |last4=Pravdo |name-list-style=amp |date=January 13, 2000 |volume=403 |pages=165–166 |doi=10.1038/35003128 |pmid=10646594 |issue= 6766 |bibcode=2000Natur.403..165R |s2cid=4303533}}</ref> Shortly thereafter,  the [[LINEAR]] survey provided an alternative estimate  of {{val|1227|+170|-90|fmt=commas}}.<ref name="LINEAR-asteroid-census">{{cite journal |title=A Near-Earth Asteroid Population Estimate from the LINEAR Survey |journal=Science |first=J. S. |last=Stuart |date=November 23, 2001 |volume=294 |issue=5547 |pages=1691–1693 |doi=10.1126/science.1065318 |pmid=11721048 |bibcode=2001Sci...294.1691S |s2cid=37849062}}</ref> In 2011, on the basis of NEOWISE observations, the estimated number of one-kilometer NEAs was narrowed to {{val|981|19}} (of which 93% had been discovered at the time), while the number of NEAs larger than 140 meters across was estimated at {{val|13200|1900|fmt=commas}}.<ref name="pia14734"/><ref name="WISE-asteroid-census">{{cite journal |title=NEOWISE Observations of Near-Earth Objects: Preliminary Results |display-authors=3|journal=[[The Astrophysical Journal]] |first1=A. |last1=Mainzer |first2=T. |last2=Grav |first3=J. |last3=Bauer |first4=J. |last4=Masiero |first5=R. S. |last5=McMillan |first6=R. M. |last6=Cutri |first7=R. |last7=Walker |first8=E. |last8=Wright |first9=P. |last9=Eisenhardt |first10=D. J. |last10=Tholen |first11=T. |last11=Spahr |first12=R. |last12=Jedicke |first13=L. |last13=Denneau |first14=E. |last14=DeBaun |first15=D. |last15=Elsbury |first16=T. |last16=Gautier |first17=S. |last17=Gomillion |first18=E. |last18=Hand |first19=W. |last19=Mo |first20=J. |last20=Watkins |first21=A. |last21=Wilkins |first22=G. L. |last22=Bryngelson |first23=A. |last23=Del Pino Molina |first24=S. |last24=Desai |first25=M. |last25=Go'mez Camus |first26=S. L. |last26=Hidalgo |first27=I. |last27=Konstantopoulos |first28=J. A. |last28=Larsen |first29=C. |last29=Maleszewski |first30=M. A. |last30=Malkan |first31=J.-C. |last31=Mauduit |first32=B. L. |last32=Mullan |first33=E. W. |last33=Olszewski |first34=J. |last34=Pforr |first35=A. |last35=Saro |first36=J. V. |last36=Scotti |first37=L. H. |last37=Wasserman |date=December 20, 2011 |volume=743 |issue=2 |page=156 |arxiv = 1109.6400 |bibcode = 2011ApJ...743..156M |doi = 10.1088/0004-637X/743/2/156 |s2cid=239991}}</ref> The NEOWISE estimate differed from other estimates primarily in assuming a slightly lower average asteroid albedo, which produces larger estimated diameters for the same asteroid brightness. This resulted in 911 then known asteroids at least 1&nbsp;km across, as opposed to the 830 then listed by CNEOS from the same inputs but assuming a slightly higher albedo.<ref>{{cite news |first=Kelly |last=Beatty |title=WISE's Survey of Near-Earth Asteroids |date=September 30, 2011 |work=Sky & Telescope |url=http://www.skyandtelescope.com/astronomy-news/wises-survey-of-near-earth-asteroids/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231024233026/https://skyandtelescope.org/astronomy-news/wises-survey-of-near-earth-asteroids/ |archive-date=October 24, 2023}}</ref> In 2017, two studies using an improved statistical method reduced the estimated number of NEAs brighter than absolute magnitude 17.75 (approximately over one kilometer in diameter) slightly to {{val|921|20}}.<ref name="NEA1km-est-2017">{{cite news |first=Matt |last=Williams |title=Good News Everyone! There are Fewer Deadly Undiscovered Asteroids than we Thought |date=October 20, 2017 |work=[[Universe Today]] |url=https://www.universetoday.com/137583/good-news-everyone-less-deadly-undiscovered-asteroids-thought/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171104064609/https://www.universetoday.com/137583/good-news-everyone-less-deadly-undiscovered-asteroids-thought/ |archive-date=November 4, 2017}}</ref><ref name="Tricario"/> The estimated number of near-Earth asteroids brighter than absolute magnitude of 22.0 (approximately over 140&nbsp;m across) rose to {{val|27100|2200|fmt=commas}}, double the WISE estimate, of which about a fourth were known at the time.<ref name="Tricario">{{cite journal |first=Pasquale |last=Tricarico |title=The near-Earth asteroid population from two decades of observations |journal=Icarus |volume=284 |pages=416–423 |date=March 1, 2017 |url=http://orbit.psi.edu/~tricaric/pdf/Tricarico_NEA_population_Icarus_2017.pdf |access-date=March 10, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20180310073945/http://orbit.psi.edu/~tricaric/pdf/Tricarico_NEA_population_Icarus_2017.pdf |archive-date=March 10, 2018 |doi=10.1016/j.icarus.2016.12.008 |arxiv=1604.06328 |bibcode=2017Icar..284..416T |s2cid=85440139}}</ref> The number of asteroids brighter than {{nowrap|H {{=}} 25}}, which corresponds to about {{convert|40|m|ft|abbr=on}} in diameter, is estimated at {{val|840000|23000|fmt=commas}}—of which about 1.3 percent had been discovered by February 2016; the number of asteroids brighter than {{nowrap|H {{=}} 30}} (larger than {{convert|3.5|m|ft|abbr=on}}) is estimated at {{val|400|100}} million—of which about 0.003 percent had been discovered by February 2016.<ref name="Tricario"/>

A September 2021 study revised the estimated number of NEAs with a diameter larger than 1&nbsp;km (using both WISE data and the absolute brightness lower than 17.75 as proxy) slightly upwards to {{val|981|19}}, of which 911 were discovered at the time, but reduced the estimated number of asteroids brighter than absolute magnitude of 22.0 (as proxy for a diameter of 140&nbsp;m) to under 20,000, of which about half were discovered at the time.<ref name="HarrisChodas2021"/><!-- The 140 m numbers can only be read from Figure 15 in the article, the completion ratio is explicitly "~50%" in the text--> The 2023 study that re-evaluated the relationship of average absolute brightness, albedo and diameter confirmed the ratios of the number of discovered and estimated total asteroids of different sizes in the 2021 study<!-- See pages 11 & 12 of the 2023 study. Based solely on brightness-diameter modelling, their completeness ratios are 88% for H <= 17.75 and 38% for H <= 23, but state that NEOWISE data outside of their model adds 6% 1 km objects and the competeness is 44% for 140 m objects.-->, but by changing the proxy for a diameter of 140&nbsp;m to {{nowrap|H {{=}} 23}}, it estimated that only about 44% of the estimated 35,000 total larger than that have been discovered by the end of 2022.<ref name="Grav2023"/> {{As of|2024|1|df=US}}, NEO catalogues still use {{nowrap|H {{=}} 22}} as proxy for a diameter of 140&nbsp;m.<ref name="CNEOS-NEO-groups"/>

{{As of|2024|12|30|df=US}}, and using diameters mostly estimated crudely from a measured absolute magnitude and an assumed albedo, 867 NEAs listed by CNEOS, including 152 PHAs, measure at least 1&nbsp;km in diameter, and 11,167 known NEAs, including 2,465 PHAs, are larger than 140&nbsp;m in diameter.<ref name="neo-jpl-stats"/>

The smallest known near-Earth asteroid is {{mp|2015 FF|415}} with an absolute magnitude of 34.34,<ref name="JPL-SSD-NEA"/> corresponding to an estimated diameter of about {{convert|0.5|m|ft|abbr=on}}.<ref name="h" /> The largest such object is [[1036 Ganymed]],<ref name="JPL-SSD-NEA"/> with an absolute magnitude of 9.18 and directly measured irregular dimensions which are equivalent to a diameter of about {{convert|38|km|mi|abbr=on}}.<ref>{{cite web |title=1036 Ganymed (A924 UB) |date=January 2, 2024 |publisher=NASA/JPL |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1036 |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250103105326/https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1036 |archive-date=January 3, 2025}}</ref>

==== Orbital classification ====
[[File:Neo orbit types.jpg|thumb|upright=1.4|NEA orbital groups (NASA/JPL)]]
Near-Earth asteroids are divided into groups based on their [[semi-major axis]] (a), [[Apsis|perihelion]] distance (q), and [[Apsis|aphelion]] distance (Q):<ref name="CNEOS-NEO-groups"/><ref name="NEOCC-DA"/>
* The ''[[Atira asteroid|Atiras]]'' or ''Apoheles'' have orbits strictly inside Earth's orbit: an Atira asteroid's aphelion distance (Q) is smaller than Earth's perihelion distance (0.983&nbsp;AU). That is, {{nowrap|Q < 0.983 AU}}, which implies that the asteroid's semi-major axis is also less than 0.983 AU.<ref name="atiras">{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=August 1, 2019 |title=Understanding the evolution of Atira-class asteroid 2019 AQ<sub>3</sub>, a major step towards the future discovery of the Vatira population |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume= 487 |issue= 2 |pages= 2742–2752 |arxiv=1905.08695 |bibcode=2019MNRAS.487.2742D |doi=10.1093/mnras/stz1437 |doi-access=free |s2cid=160009327}}</ref> This group includes asteroids on orbits that never get close to Earth, including the sub-group of [[Atira asteroid#ꞌAylóꞌchaxnim asteroids|ꞌAylóꞌchaxnims]], which orbit the Sun entirely within the orbit of [[Venus (planet)|Venus]]<ref>{{cite journal |last1=Bolin |first1=Bryce T. |display-authors=et al |date=November 2022 |title=The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=517 |issue=1 |pages=L49–L54 |doi=10.1093/mnrasl/slac089 |doi-access=free |arxiv=2208.07253}}</ref> and which include the hypothetical sub-group of [[Vulcanoid]]s, which have orbits entirely within the orbit of [[Mercury (planet)|Mercury]].<ref>{{cite news |first=David |last=Dickinson |title=Astronomers Discover Asteroid that Flies Close to the Sun |date=August 25, 2021 |work=Sky & Telescope |url=https://skyandtelescope.org/astronomy-blogs/astronomy-space-david-dickinson/astronomers-discover-asteroid-that-flies-close-to-the-sun/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241130073024/https://skyandtelescope.org/astronomy-blogs/astronomy-space-david-dickinson/astronomers-discover-asteroid-that-flies-close-to-the-sun/ |archive-date=November 30, 2024}}</ref>
* The ''[[Aten asteroid|Atens]]'' have a semi-major axis of less than 1&nbsp;AU and cross Earth's orbit. Mathematically, {{nowrap|a < 1.0 AU}} and {{nowrap|Q > 0.983 AU}}. (0.983 AU is Earth's perihelion distance.)
* The ''[[Apollo asteroid|Apollos]]'' have a semi-major axis of more than 1&nbsp;AU and cross Earth's orbit. Mathematically, {{nowrap|a > 1.0 AU}} and {{nowrap|q < 1.017 AU}}. (1.017&nbsp;AU is Earth's aphelion distance.)
* The ''[[Amor asteroid|Amors]]'' have orbits strictly outside Earth's orbit: an Amor asteroid's perihelion distance (q) is greater than Earth's aphelion distance (1.017&nbsp;AU). Amor asteroids are also near-Earth objects so {{nowrap|q < 1.3 AU}}. In summary, {{nowrap|1.017 AU < q < 1.3 AU}}. (This implies that the asteroid's semi-major axis (a) is also larger than 1.017&nbsp;AU.) Some Amor asteroid orbits cross the orbit of Mars.

Some authors define Atens differently: they define it as being all the asteroids with a semi-major axis of less than 1&nbsp;AU.<ref>{{cite web |title=Unusual Minor Planets |publisher=IAU/MPC |url=https://minorplanetcenter.net/iau/Unusual.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241130124156/https://minorplanetcenter.net/iau/Unusual.html |archive-date=November 30, 2024}}</ref><ref name="galache"/> That is, they consider the Atiras to be part of the Atens.<ref name="galache">{{cite web |first=J. L. |last=Galache |title=Asteroid Classification I – Dynamics |publisher=IAU/MPC |date=March 5, 2011 |url=http://minorplanetcenter.net/blog/asteroid-classification-i-dynamics/ |access-date=March 9, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20160303235814/http://minorplanetcenter.net/blog/asteroid-classification-i-dynamics/ |archive-date=March 3, 2016}}</ref> Historically, until 1998, there were no known or suspected Atiras, so the distinction wasn't necessary.

Atiras and Amors do not cross the Earth's orbit and are not immediate impact threats, but their orbits may change to become Earth-crossing orbits in the future.<ref name="MorbidelliAstIII"/><ref>{{Cite journal |last1=Ribeiro |first1=A. O. |last2=Roig |first2=F.|last3=De Prá |first3=M. N. |last4=Carvano |first4=J. M. |last5=DeSouza |first5=S. R. |title=Dynamical study of the Atira group of asteroids |date=March 17, 2016 |journal=Monthly Notices of the Royal Astronomical Society |volume=458 |issue=4 |pages=4471–4476 |doi=10.1093/mnras/stw642 |issn=0035-8711 |doi-access=free}}</ref>

{{As of|2024|12|30|df=US}}, 34 Atiras, 2,952 Atens, 21,132 Apollos and 13,137 Amors have been discovered and cataloged.<ref name="neo-jpl-stats" />

==== Co-orbital asteroids ====
[[File:Lagrange Horseshoe Orbit.jpg|thumb|The five Lagrangian points relative to the Sun and Earth and possible orbits along gravitational contours]]

Most NEAs have orbits that are significantly more [[Orbital eccentricity|eccentric]] than that of the Earth and the other major planets and their orbital planes can [[Orbital inclination|tilt]] several degrees relative to that of the Earth. NEAs which have orbits that do resemble the Earth's in eccentricity, inclination and semi-major axis are grouped as [[Arjuna asteroid]]s.<ref name="2023FY3_2024"/> Within this group are NEAs that have the same orbital period as the Earth, or a [[co-orbital configuration]], which corresponds to an [[orbital resonance]] at a ratio of 1:1. All co-orbital asteroids have special orbits that are relatively stable and, paradoxically, can prevent them from getting close to Earth:
* ''[[Trojan (astronomy)|Trojans]]'': Near the orbit of a planet, there are five gravitational equilibrium points, the [[Lagrangian point]]s, in which an asteroid would orbit the Sun in fixed formation with the planet. Two of these, 60 degrees ahead and behind the planet along its orbit (designated L4 and L5 respectively) are stable; that is, an asteroid near these points would stay there for thousands or even millions of years in spite of light perturbations by other planets and by non-gravitational forces. Trojans circle around L4 or L5 on paths resembling a [[tadpole]].<ref name="Fuentes-horseshoe"/> {{As of|2023|10}}, Earth has two confirmed Trojans:<ref name="CastroCisneros2023"/> {{mpl|(706765) 2010 TK|7}} and {{mpl|(614689) 2020 XL|5}}, both circling Earth's L4 point.<ref name="WISE">{{cite press release |title=NASA's WISE mission finds first Trojan asteroid sharing Earth's orbit |date=July 27, 2011 |work=PR Newswire |publisher=[[NASA]] |url=https://www.prnewswire.com/news-releases/nasas-wise-mission-finds-first-trojan-asteroid-sharing-earths-orbit-126277963.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240127131203/https://www.prnewswire.com/news-releases/nasas-wise-mission-finds-first-trojan-asteroid-sharing-earths-orbit-126277963.html |archive-date=January 27, 2024}}</ref><ref name="Trojan2">{{cite news |first=Chelsea |last=Gohd |title=Earth has an extra companion, a Trojan asteroid that will hang around for 4,000 years |date=February 1, 2022 |work=Space.com |url=https://www.space.com/earth-extra-moon-trojan-asteroid-2020-xl5-discovery |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241208100907/https://www.space.com/earth-extra-moon-trojan-asteroid-2020-xl5-discovery |archive-date=December 8, 2024}}</ref>
* ''[[Horseshoe orbit|Horseshoe librators]]'': The region of stability around L4 and L5 also includes orbits for co-orbital asteroids that run around both L4 and L5. Relative to the Earth and Sun, the orbit can resemble the circumference of a horseshoe, or may consist of annual loops that wander back and forth ([[Libration|librate]]) in a horseshoe-shaped area. In both cases, the Sun is at the horseshoe's center of gravity, Earth is in the gap of the horseshoe, and L4 and L5 are inside the ends of the horseshoe. Among Earth's known co-orbitals, those with the most stable orbits as well as those with the least stable orbits are horseshoe librators.<ref name="Fuentes-horseshoe">{{cite journal |last1=de&nbsp;la&nbsp;Fuente Marcos |first1=C. |last2=de&nbsp;la&nbsp;Fuente Marcos |first2=R. |title=A trio of horseshoes: Past, present, and future dynamical evolution of Earth co-orbital asteroids {{mp|2015 XX|169}}, {{mp|2015 YA}} and {{mp|2015 YQ|1}} |journal=[[Astrophysics and Space Science]] |volume=361 |issue=4 |pages=121–133 |date=April 2016 |doi=10.1007/s10509-016-2711-6 |arxiv=1603.02415 |bibcode=2016Ap&SS.361..121D |s2cid=119222384}}</ref> {{As of|2023|10}}, at least 13 horseshoe librators of Earth have been discovered.<ref name="CastroCisneros2023"/> The most-studied and, at about {{convert|5|km|mi|abbr=on}}, largest is [[3753 Cruithne]], which travels along bean-shaped annual loops and completes its horseshoe libration cycle every 770–780 years.<ref>{{cite journal |title=An asteroidal companion to the Earth |type=letter |last1=Wiegert |first1=Paul A. |last2=Innanen |first2=Kimmo A. |last3=Mikkola |first3=Seppo |journal=Nature |date=June 12, 1997 |volume=387 |issue=6634 |pages=685–686 |doi=10.1038/42662 |bibcode=1997Natur.387..685W |s2cid=4305272 |url=http://www.astro.uwo.ca/~pwiegert/papers/1997Nature.387.685.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203022402/https://physics.uwo.ca/~pwiegert/papers/1997Nature.387.685.pdf |archive-date=December 3, 2024}}</ref><ref>{{cite web |first=Brad |last=Snowder |title=Cruithne |publisher=Western Washington University Planetarium |url=https://astro101.wwu.edu/a101_cruithne.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240101150817/https://astro101.wwu.edu/a101_cruithne.html |archive-date=January 1, 2024}}</ref> {{mpl|419624|2010 SO|16}} is an asteroid on a relatively stable circumference-of-a-horseshoe orbit, with a horseshoe [[libration]] period of about 350 years.<ref>{{cite journal |last1=Christou |first1=A.A. |last2=Asher |first2=D.J. |title=A long-lived horseshoe companion to the Earth |date=July 11, 2011 |journal=Monthly Notices of the Royal Astronomical Society |volume=414 |issue=4 |pages=2965–2969 |doi=10.1111/j.1365-2966.2011.18595.x |doi-access=free |arxiv=1104.0036 |bibcode=2011MNRAS.414.2965C |s2cid=13832179}}</ref>
* ''[[Quasi-satellite]]s'': Quasi-satellites are co-orbital asteroids on a normal elliptic orbit with a higher eccentricity than Earth's, which they travel in a way synchronised with Earth's motion. Since the asteroid orbits the Sun slower than Earth when further away and faster than Earth when closer to the Sun, when observed in a rotating frame of reference fixed to the Sun and the Earth, the quasi-satellite appears to orbit Earth in a [[retrograde motion|retrograde]] direction in one year, even though it is not bound gravitationally. {{As of|2023|10}}, six asteroids were known to be a quasi-satellite of Earth.<ref name="CastroCisneros2023"/> [[469219 Kamoʻoalewa]] is Earth's closest quasi-satellite, in an orbit that has been stable for almost a century.<ref name="Fuentes-2016HO3">{{cite journal |last1=de&nbsp;la&nbsp;Fuente Marcos |first1=C. |last2=de&nbsp;la&nbsp;Fuente Marcos |first2=R. |title=Asteroid {{mp|469219|2016 HO|3}}, the smallest and closest Earth quasi-satellite |journal=Monthly Notices of the Royal Astronomical Society |volume=462 |issue=4 |pages=3441–3456 |date=November 11, 2016 |doi=10.1093/mnras/stw1972 |doi-access=free |arxiv=1608.01518 |bibcode=2016MNRAS.462.3441D |s2cid=118580771}}</ref> This asteroid is thought to be a piece of the Moon ejected during an impact.<ref name="CastroCisneros2023">{{cite journal |first1=Jose Daniel |last1=Castro-Cisneros |first2=Renu |last2=Malhotra |first3=Aaron J. |last3=Rosengren |title=Lunar ejecta origin of near-Earth asteroid Kamo'oalewa is compatible with rare orbital pathways |date=October 23, 2023 |journal=[[Communications Earth & Environment]] |volume=4 |issue=1 |at=section 372 |doi=10.1038/s43247-023-01031-w |pmid=39524985 |pmc=11549049 |arxiv=2304.14136 |bibcode=2023ComEE...4..372C}}</ref><ref>{{cite news |first=Robert |last=Lea |title=Earth's weird 'quasi-moon' Kamo'oalewa is a fragment blasted out of big moon crater |date=April 23, 2024 |work=Space.com |url=https://www.space.com/quasi-moon-kamooalewa-giant-lunar-impact |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241224181137/https://www.space.com/quasi-moon-kamooalewa-giant-lunar-impact |archive-date=December 24, 2024}}</ref> Orbit calculations show that almost all quasi-satellites and many horseshoe librators repeatedly transfer between horseshoe and quasi-satellite orbits.<ref name="Fuentes-2016HO3"/><ref name="DiRuzza2023">{{cite journal |first1=Sara |last1=Di Ruzza |first2=Alexandre |last2=Pousse |first3=Elisa Maria |last3=Alessi |title=On the co-orbital asteroids in the solar system: medium-term timescale analysis of the quasi-coplanar objects |date=January 15, 2023 |journal=Icarus |volume=390 |at=section 115330 |article-number=115330 |doi=10.1016/j.icarus.2022.115330 |arxiv=2209.05219 |bibcode=2023Icar..39015330D}}</ref> One of these objects, {{mpl|2003 YN|107}}, was observed during its transition from a quasi-satellite orbit to a horseshoe orbit in 2006; it is expected to transfer back to a quasi-satellite orbit sometime around year 2066.<ref>{{cite news |first=Tony |last=Phillips |title=Corkscrew asteroid |date=June 9, 2006 |work=Science@NASA |publisher=[[NASA]] |url=http://science.nasa.gov/headlines/y2006/09jun_moonlets.htm |access-date=November 13, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20060929155325/http://science.nasa.gov/headlines/y2006/09jun_moonlets.htm |archive-date=September 29, 2006}}</ref> A quasi-satellite discovered in 2023 but then found in old photographs back to 2012, {{mpl|2023 FW|13}}, was found to have an orbit that is stable for about 4,000 years, from 100 BC to AD 3700.<ref>{{cite news |first=David L. |last=Chandler |title=Astronomers have discovered an asteroid that orbits the Sun with Earth, earning it the moniker "quasi-moon." |date=April 7, 2023 |work=Sky & Telescope |url=https://skyandtelescope.org/astronomy-news/does-earth-have-new-quasi-moon/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240721235051/https://skyandtelescope.org/astronomy-news/does-earth-have-new-quasi-moon/ |archive-date=July 21, 2024}}</ref>
* Asteroids on ''compound orbits'': orbital calculations show that some co-orbital asteroids transit between horseshoe and quasi-satellite orbits during every horseshoe resp. quasi-satellite cycle. Theoretically, similar continuous transitions between Trojan and horseshoe orbits are possible, too. {{As of|2023|1}}, at least 20 Earth co-orbital NEAs are thought to be in the horseshoe-like phase of compound orbits.<ref name="DiRuzza2023"/>
[[File:Animation of 2020 CD3's orbit around Earth.gif|thumb|Animation of {{mpl|2020 CD|3}}'s orbit around Earth<br />{{legend2|Magenta|{{mp|2020 CD|3}}}}{{·}}{{legend2|DarkKhaki|Moon}}{{·}}{{legend2|RoyalBlue|Earth}}]]
* ''[[Temporary satellite]]s'': NEAs can also transfer between solar orbits and distant Earth orbits, becoming gravitationally bound temporary satellites. According to simulations, temporary satellites are typically caught when they pass Earth's L1 or L2 Lagrangian points at the time Earth is either at the point in its orbit closest or farthest from the Sun, complete a couple of orbits around Earth, and then return to a heliocentric orbit due to perturbations from the Moon.<ref name="ST111230">{{cite news |first=Camille M. |last=Carlisle |title=Pseudo-moons orbit Earth |date=December 30, 2011 |work=Sky & Telescope |url=https://skyandtelescope.org/astronomy-news/pseudo-moons-orbit-earth/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240530185354/https://skyandtelescope.org/astronomy-news/pseudo-moons-orbit-earth/ |archive-date=May 30, 2024}}</ref> Strictly speaking, temporary satellites aren't co-orbital asteroids, and they can have orbits of the broader Arjuna type before and after capture by Earth, but simulations show that they can be captured from, or transfer to, horseshoe orbits.<ref name="2023FY3_2024"/> The simulations also indicate that Earth typically has at least one temporary satellite {{convert|1|m|ft|abbr=on}} across at any given time, but they are too faint to be detected by current surveys.<ref name="ST111230"/> {{As of|2024|12}}, five temporary satellites have been observed:<ref name="2023FY3_2024"/> {{mpl|1991 VG|}},<ref name="Fuente-Marcos-2018">{{Cite journal |first1=Carlos |last1=de la Fuente Marcos |first2=Raúl |last2=de la Fuente Marcos |date= January 2018 |title=Dynamical evolution of near-Earth asteroid 1991 VG |journal=Monthly Notices of the Royal Astronomical Society |volume=473 |issue=3 |pages=2939–2948 |bibcode=2018MNRAS.473.2939D |doi=10.1093/mnras/stx2545  |doi-access=free |arxiv=1709.09533}}</ref> {{mpl|2006 RH|120}}, {{mpl|2020 CD|3}},<ref>{{cite news |first=Roger W. |last=Sinnott |title=Earth's "other moon" |date=April 17, 2007 |work=Sky & Telescope |url=https://skyandtelescope.org/astronomy-news/earths-other-moon/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241130072820/https://skyandtelescope.org/astronomy-news/earths-other-moon/ |archive-date=November 30, 2024}}</ref><ref name="Naidu2020">{{cite news |first1=Shantanu |last1=Naidu |last2=Farnocchia |first2=Davide |title=Tiny Object Discovered in Distant Orbit Around the Earth |date=February 27, 2020 |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/news/news205.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241219113203/https://cneos.jpl.nasa.gov/news/news205.html |archive-date=December 19, 2024}}</ref> {{mpl|2022 NX|1}}<ref name="2023FY3_2024"/> and {{mpl|2024 PT|5}}.<ref>{{cite news |first=Robert |last=Lea |title=Earth's mini-moon has finally departed. Will it ever return as a 'second moon?' |date=November 26, 2024 |work=Space.com |url=https://www.space.com/goodnight-second-moon-asteroid-2024PT5 |access-date=January 1, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101183548/https://www.space.com/goodnight-second-moon-asteroid-2024PT5 |archive-date=January 1, 2025}}</ref> Calculations for the {{convert|5|m|ft|abbr=on}} asteroid {{mpl|2023 FY|3}} showed repeated transitions into temporary satellite orbits both in the past and the future 10,000 years.<ref name="2023FY3_2024">{{cite journal |first1=R. |last1=de&nbsp;la&nbsp;Fuente Marcos |first2=C. |last2=de&nbsp;la&nbsp;Fuente Marcos |display-authors=etal |title=When the horseshoe fits: Characterizing {{mp|2023 FY|3}} with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope |date=January 2024 |journal=Astronomy & Astrophysics |volume=681 |at=section A4 |doi=10.1051/0004-6361/202347663 |arxiv=2310.08724 |bibcode=2024A&A...681A...4D}}</ref>

Near-Earth asteroids also include the co-orbitals of Venus. {{As of|2023|1}}, all known co-orbitals of Venus have orbits with high eccentricity, also crossing Earth's orbit.<ref name="DiRuzza2023"/><ref>{{cite journal |first1=Petr |last1=Pokorý |first2=Marc |last2=Kuchner |title=Threat from Within: Excitation of Venus's Co-orbital Asteroids to Earth-crossing Orbits |date=October 2021 |journal=The Planetary Science Journal |volume=2 |issue=5 |at=part 193 |doi=10.3847/PSJ/ac1e9b |doi-access=free |bibcode=2021PSJ.....2..193P}}</ref>

=== Meteoroids ===

In 1961, the IAU defined [[meteoroid]]s as a class of solid interplanetary objects distinct from asteroids by their considerably smaller size.<ref name="Rubin2010"/> This definition was useful at the time because, with the exception of the [[Tunguska event]], all historically observed meteors were produced by objects significantly smaller than the smallest asteroids then observable by telescopes.<ref name="Rubin2010"/> As the distinction began to blur with the discovery of ever smaller asteroids and a greater variety of observed NEO impacts, revised definitions with size limits have been proposed from the 1990s.<ref name="Rubin2010">{{cite journal |last1=Rubin |first1=Alan E. |last2=Grossman |first2=Jeffrey N. |title=Meteorite and meteoroid: New comprehensive definitions |journal=Meteoritics & Planetary Science |volume=45 |issue=1 |pages=114–122 |date=January 2010 |doi=10.1111/j.1945-5100.2009.01009.x |bibcode=2010M&PS...45..114R |s2cid=129972426}}</ref> In April 2017, the IAU adopted a revised definition that generally limits meteoroids to a size between 30&nbsp;μm and 1&nbsp;m in diameter, but permits the use of the term for any object of any size that caused a meteor, thus leaving the distinction between asteroid and meteoroid blurred.<ref name="met-def-2017">{{cite news |first=Vincent |last=Perlerin |title=Definitions of terms in meteor astronomy (IAU) |date=September 26, 2017 |work=News |publisher=[[International Meteor Organization]] |url=https://www.imo.net/definitions-of-terms-in-meteor-astronomy-iau/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20180123072313/https://www.imo.net/definitions-of-terms-in-meteor-astronomy-iau/ |archive-date=January 23, 2018}}</ref>

=== Near-Earth comets<!--'Near-Earth comet' and 'Near-Earth comets' redirect here--> ===

[[File:Halley's Comet - May 29 1910.jpg|thumb|[[Halley's Comet]] during its 0.10&nbsp;AU<ref>{{cite web |first=Donald K. |last=Yeomans |title=Great Comets in History |date=April 2007 |publisher=NASA/JPL |url=https://ssd.jpl.nasa.gov/sb/great_comets.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240126111145/https://ssd.jpl.nasa.gov/sb/great_comets.html |archive-date=January 26, 2024}}</ref> approach of Earth in May 1910]]

'''Near-Earth comets'''<!--boldface per WP:R#PLA--> (NECs) are objects in a near-Earth orbit with a tail or coma made up of dust, gas or ionized particles emitted by a solid nucleus. Comet nuclei are typically less dense than asteroids but they pass Earth at higher relative speeds, thus the impact energy of a comet nucleus is slightly larger than that of a similar-sized asteroid.<ref name="NEOSDT2003"/> NECs may pose an additional hazard due to fragmentation: the meteoroid streams which produce meteor showers may include large inactive fragments, effectively NEAs.<ref name="Jenniksens2005">{{Cite conference |last=Jenniksens |first=Peter |title=Meteor Showers from Broken Comets |date=September 2005 |conference=Workshop on Dust in Planetary Systems (ESA SP-643) |volume=643 |pages=3–6 |bibcode=2007ESASP.643....3J}}</ref> Although no impact of a comet in Earth's history has been conclusively confirmed, the [[Tunguska event]] may have been caused by a fragment of [[Comet Encke]].<ref>{{cite journal |last=Kresak| first=L'.l |title=The Tunguska object – A fragment of Comet Encke |bibcode=1978BAICz..29..129K |volume=29 |date=1978 |pages=129 |journal=Bulletin of the Astronomical Institutes of Czechoslovakia}}</ref>

Comets are commonly divided between short-period and long-period comets. Short-period comets, with an orbital period of less than 200 years, originate in the [[Kuiper belt]], beyond the orbit of [[Neptune]]; while long-period comets originate in the [[Oort Cloud]], in the outer reaches of the Solar System.<ref name="TaskForceReport"/> The orbital period distinction is of importance in the evaluation of the risk from near-Earth comets because short-period NECs are likely to have been observed during multiple apparitions and thus their orbits can be determined with some precision, while long-period NECs can be assumed to have been seen for the first and last time when they appeared since the start of precise observations, thus their approaches cannot be predicted well in advance.<ref name="TaskForceReport">{{cite book |author=<!--Staff writer(s); no by-line.--> |title=Report of the Task Force on potentially hazardous Near Earth Objects |location=London |publisher=British National Space Centre |date=September 2000 |url=https://spaceguardcentre.com/wp-content/uploads/2014/04/full_report.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241208153948/https://spaceguardcentre.com/wp-content/uploads/2014/04/full_report.pdf |archive-date=December 8, 2024}}</ref> Since the threat from long-period NECs is estimated to be at most 1% of the threat from NEAs, and long-period comets are very faint and thus difficult to detect at large distances from the Sun, Spaceguard efforts have consistently focused on asteroids and short-period comets.<ref name="Vulcano1995"/><ref name="NEOSDT2003">{{cite book |author=<!--Staff writer(s); no by-line.--> |title=Study to Determine the Feasibility of Extending the Search for Near-Earth Objects to Smaller Limiting Diameters |date=August 22, 2003 |publisher=NASA |url=https://cneos.jpl.nasa.gov/doc/neoreport030825.pdf |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241212090955/https://cneos.jpl.nasa.gov/doc/neoreport030825.pdf |archive-date=December 12, 2024}}</ref> Both NASA's CNEOS<ref name="CNEOS-NEO-groups"/> and ESA's NEOCC<ref name="NEOCC-DA"/> restrict their definition of NECs to short-period comets. {{As of|2024|12|30|df=US}}, 123 such objects have been discovered.<ref name="neo-jpl-stats" />

[[Comet Swift-Tuttle|Comet 109P/Swift–Tuttle]], which is also the source of the [[Perseids|Perseid meteor shower]] every year in August, has a roughly 130-year orbit that passes close to the Earth. During the comet's September 1992 recovery, when only the two previous returns in 1862 and 1737 had been identified, calculations showed that the comet would pass close to Earth during its next return in 2126, with an impact within the range of uncertainty. By 1993, even earlier returns (back to at least 188 AD) had been identified, and the longer observation arc eliminated the impact risk. The comet will pass Earth in 2126 at a distance of 23 million kilometers. In 3044, the comet is expected to pass Earth at less than 1.6 million kilometers.<ref>{{cite web |first=Sally | last=Stephens |title=What about the comet that's supposed to hit the Earth in 130 years? |date=1993 |work=Cosmic Collisions |publisher=[[Astronomical Society of the Pacific]] |url=https://astrosociety.org/file_download/inline/245c66de-59dd-49e9-8773-16ef08de09ff |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231003194758/https://www.astrosociety.org/file_download/inline/245c66de-59dd-49e9-8773-16ef08de09ff |archive-date=October 3, 2023}}</ref>

=== Artificial near-Earth objects ===
[[Image:J002e3 animated.gif|thumb|[[J002E3]] discovery images taken on September 3, 2002. J002E3 is in the circle]]
Defunct [[Uncrewed spacecraft|space probes]] and [[Multistage rocket|final stages of rockets]] can end up in near-Earth orbits around the Sun. Examples of such artificial near-Earth objects include a [[Elon Musk's Tesla Roadster|Tesla Roadster]] used as [[Boilerplate (spaceflight)|dummy payload]] in a 2018 rocket test<ref>{{cite web |title=Tesla Roadster (spacecraft) (solution #10) |date=March 27, 2018 |work=[[JPL Horizons On-Line Ephemeris System]] |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=-143205&CENTER='500@10'&MAKE_EPHEM=YES&TABLE_TYPE=ELEMENTS&START_TIME=2018-05-01&STOP_TIME='2018-05-01+00:00:01'&OUT_UNITS=AU-D&REF_PLANE=ECLIPTIC&REF_SYSTEM=J2000&TP_TYPE=ABSOLUTE&ELEM_LABELS=YES&CSV_FORMAT=NO&OBJ_DATA=YES |access-date=December 31, 2024 |url-status=live |archive-date=June 30, 2019 |archive-url=https://web.archive.org/web/20190630211314/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=-143205&CENTER=%27500@10%27&MAKE_EPHEM=YES&TABLE_TYPE=ELEMENTS&START_TIME=2018-05-01&STOP_TIME=%272018-05-01+00:00:01%27&OUT_UNITS=AU-D&REF_PLANE=ECLIPTIC&REF_SYSTEM=J2000&TP_TYPE=ABSOLUTE&ELEM_LABELS=YES&CSV_FORMAT=NO&OBJ_DATA=YES}}</ref> and the [[Kepler space telescope]].<ref>{{cite web |first1=David |last1=Koch |first2=Alan |last2=Gould |title=Kepler Mission: Launch Vehicle and Orbit |date=February 12, 2007 |publisher=NASA |url=http://kepler.nasa.gov/sci/design/orbit.html |access-date=March 14, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20070622161529/http://kepler.nasa.gov/sci/design/orbit.html |archive-date=June 22, 2007}}</ref> Some of these objects have been re-discovered by NEO surveys when they returned to Earth's vicinity and classified as asteroids before their artificial origin was recognised.

An object classified as asteroid [[1991 VG]] was discovered during its transition from a temporary satellite orbit around Earth to a solar orbit in November 1991, and could only be observed until April 1992. Some scientists suspected it to be a returning piece of man-made space debris. After new observations in 2017 provided better data on its orbit and surface characteristics, a new study found the artificial origin unlikely.<ref name="Fuente-Marcos-2018"/>

In September 2002, astronomers found an object designated [[J002E3]]. The object was on a temporary satellite orbit around Earth, leaving for a solar orbit in June 2003. Calculations showed that it was also on a solar orbit before 2002, but was close to Earth in 1971. J002E3 was identified as the third stage of the [[Saturn V]] rocket that carried [[Apollo 12]] to the Moon.<ref>{{cite news |first1=Steve |last1=Chesley |first2=Paul |last2=Chodas |title=J002E3: An Update |date=October 9, 2002 |work=News |publisher=NASA/JPL |url=http://neo.jpl.nasa.gov/news/news136.html |access-date=November 14, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20030503111617/http://neo.jpl.nasa.gov/news/news136.html |archive-date=May 3, 2003}}</ref><ref name="rocket-or-rock"/> In 2006, two more apparent temporary satellites were discovered which were suspected of being artificial.<ref name="rocket-or-rock"/> One of them was eventually confirmed as an asteroid and classified as the temporary satellite {{mp|2006 RH|120}}.<ref name="rocket-or-rock"/> The other, [[6Q0B44E]], was confirmed as an artificial object, but its identity is unknown.<ref name="rocket-or-rock"/> Another temporary satellite was discovered in 2013, and was designated {{mp|2013 QW|1}} as a suspected asteroid. It was later found to be an artificial object of unknown origin. {{mp|2013 QW|1}} is no longer listed as an asteroid by the Minor Planet Center.<ref name="rocket-or-rock">{{cite news |last=Azriel |first=Merryl |title=Rocket or Rock? NEO Confusion Abounds |date=September 25, 2013 |work=[[International Association for the Advancement of Space Safety#Space Safety Magazine|Space Safety Magazine]] |url=http://www.spacesafetymagazine.com/space-debris/satellite-tracking/rocket-or-rock/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171115143536/http://www.spacesafetymagazine.com/space-debris/satellite-tracking/rocket-or-rock/ |archive-date=November 15, 2017}}</ref><ref name="MPC_QW1">{{Cite web |title=MPC Database Search. Unknown object: 2013 QW1 |publisher=IAU/MPC |url=https://minorplanetcenter.net/db_search/show_object?object_id=2013+QW1 |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250103123618/https://minorplanetcenter.net/db_search |archive-date=January 3, 2025}}</ref> In September 2020, an object detected on an orbit very similar to that of the Earth was temporarily designated {{mpl|2020 SO|}}. However, orbital calculations and spectral observations confirmed that the object was the [[Centaur (rocket stage)|Centaur rocket booster]] of the 1966 [[Surveyor 2]] uncrewed lunar lander.<ref>{{cite news |title=Earth May Have Captured a 1960s-Era Rocket Booster |date=November 12, 2020 |work=News |publisher=NASA/JPL |url=https://www.jpl.nasa.gov/news/earth-may-have-captured-a-1960s-era-rocket-booster |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241220135930/https://www.jpl.nasa.gov/news/earth-may-have-captured-a-1960s-era-rocket-booster/ |archive-date=December 20, 2024}}</ref><ref>{{cite news |title=New Data Confirm 2020 SO to Be the Upper Centaur Rocket Booster From the 1960's |date=December 2, 2020 |work=News |publisher=NASA/JPL |url=https://www.jpl.nasa.gov/news/new-data-confirm-2020-so-to-be-the-upper-centaur-rocket-booster-from-the-1960s |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241220224200/https://www.jpl.nasa.gov/news/new-data-confirm-2020-so-to-be-the-upper-centaur-rocket-booster-from-the-1960s/ |archive-date=December 20, 2024}}</ref>

In some cases, active space probes on solar orbits have been observed by NEO surveys and erroneously catalogued as asteroids before identification. During its 2007 flyby of Earth on its route to a comet, ESA's space probe ''[[Rosetta (spacecraft)|Rosetta]]'' was detected unidentified and classified as asteroid {{mp|2007 VN|84}}, with an alert issued due to its close approach.<ref>{{cite news |first=Justin |last= Mullins |title=Astronomers defend asteroid warning mix-up |date=November 13, 2007 |work=New Scientist |url=https://www.newscientist.com/article/dn12914-astronomers-defend-asteroid-warning-mix-up/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20170307062102/https://www.newscientist.com/article/dn12914-astronomers-defend-asteroid-warning-mix-up/ |archive-date=March 7, 2017}}</ref> The designation {{mp|2015 HP|116}} was similarly removed from asteroid catalogues when the observed object was identified with ''[[Gaia (spacecraft)|Gaia]]'', ESA's [[space observatory]] for [[astrometry]].<ref>{{cite web |title=MPEC 2015-H125: Deletion Of 2015 HP116 |date=April 27, 2015 |work=Minor Planet Electronic Circular |publisher=IAU/MPC |url=http://www.minorplanetcenter.net/mpec/K15/K15HC5.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241127001828/https://minorplanetcenter.net/mpec/K15/K15HC5.html |archive-date=November 27, 2024}}</ref>

== Exploratory missions ==
{{Further|List of minor planets and comets visited by spacecraft}}

Some NEOs are of special interest because the [[Delta-v budget|sum total of changes in orbital speed]] required to send a spacecraft on a mission to physically explore an NEO – and thus the amount of rocket fuel required for the mission – is lower than what is necessary for even lunar missions, due to their combination of low velocity with respect to Earth and weak gravity. They may present interesting scientific opportunities both for direct geochemical and astronomical investigation, and as potentially economical sources of extraterrestrial materials for human exploitation.<ref name="USAToday-NEA">{{cite news |first=Dan |last=Vergano |title=Near-Earth asteroids could be 'steppingstones to Mars' |date=February 2, 2007 |work=[[USA Today]] |url=https://www.usatoday.com/tech/science/space/2007-02-12-asteroid_x.htm |access-date=November 18, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20120417034648/http://www.usatoday.com/tech/science/space/2007-02-12-asteroid_x.htm |archive-date=April 17, 2012}}</ref> This makes them an attractive target for exploration.<ref>{{cite journal |title=Design and optimization of trajectory to Near-Earth asteroid for sample return mission using gravity assists |first1=Rui |last1=Xu |first2=Pingyuan |last2=Cui |first3=Dong |last3=Qiao |first4=Enjie |last4=Luan |name-list-style=amp |journal=Advances in Space Research |volume=40 |issue=2 |pages=200–225 |date=March 18, 2007 |doi=10.1016/j.asr.2007.03.025 |bibcode=2007AdSpR..40..220X}}</ref>

=== Missions to NEAs ===
[[File:PIA02475 Eros' Bland Butterscotch Colors.jpg|thumb|Different views of [[433 Eros]] as seen by NASA's ''[[NEAR Shoemaker]]'' probe]]
[[File:Bennu mosaic OSIRIS-REx (square).png|thumb|Image mosaic of asteroid [[101955 Bennu]], target of NASA's ''[[OSIRIS-REx]]'' probe]]

The IAU held a minor planets workshop in [[Tucson, Arizona]], in March 1971. At that point, launching a spacecraft to asteroids was considered premature; the workshop only inspired the first astronomical survey specifically aiming for NEAs.<ref name="wired20130323"/> Missions to asteroids were considered again during a workshop at the [[University of Chicago]] held by NASA's Office of Space Science in January 1978. Of all of the near-Earth asteroids (NEA) that had been discovered by mid-1977, it was estimated that spacecraft could [[Space rendezvous|rendezvous]] with and return from only about 1 in 10 using less [[Spacecraft propulsion|propulsive energy]] than is necessary to reach [[Mars]]. It was recognised that due to the low surface gravity of all NEAs, moving around on the surface of an NEA would cost very little energy, and thus space probes could gather multiple samples.<ref name="wired20130323"/> Overall, it was estimated that about one percent of all NEAs might provide opportunities for [[human spaceflight|human-crewed]] missions, or no more than about ten NEAs known at the time. A five-fold increase in the NEA discovery rate was deemed necessary to make a crewed mission within ten years worthwhile.<ref name="wired20130323"/>

The first near-Earth asteroid to be visited by a spacecraft was [[433 Eros]] when [[NASA]]'s ''[[NEAR Shoemaker]]'' probe orbited it from February 2000, landing on the surface of the {{convert|17|km|mi|abbr=on}} asteroid in February 2001.<ref name="Eros-NEAR">{{cite news |first1=Donald |last1=Savage |first2=Michael |last2=Buckley |name-list-style=amp |title=NEAR Mission Completes Main Task, Now Will Go Where No Spacecraft Has Gone Before |date=January 31, 2001 |work=Press Releases |publisher=NASA |url=http://nssdc.gsfc.nasa.gov/planetary/news/near_descent_pr_20010131.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20160617001709/http://nssdc.gsfc.nasa.gov/planetary/news/near_descent_pr_20010131.html |archive-date=June 17, 2016}}</ref> A second NEA, the {{convert|535|m|ft|abbr=on}} long peanut-shaped [[25143 Itokawa]], was explored from September 2005 to April 2007 by [[JAXA]]'s ''[[Hayabusa (spacecraft)|Hayabusa]]'' mission, which succeeded in taking material samples back to Earth.<ref name="Itokawa-hayabusa">{{cite web |title=Hayabusa. The Final Approach. Overview |publisher=JAXA |url=https://hayabusa.jaxa.jp/e/index.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20230602050007/https://hayabusa.jaxa.jp/e/index.html |archive-date=June 2, 2023}}</ref> A third NEA, the {{convert|2.26|km|mi|abbr=on}} long elongated [[4179 Toutatis]], was explored by [[China National Space Administration|CNSA]]'s ''[[Chang'e 2]]'' spacecraft during a flyby in December 2012.<ref name="Toutatis-Change">{{cite news |first=Emily |last=Lakdawalla |title=Chang'e 2 imaging of Toutatis |date=December 14, 2012 |publisher=[[The Planetary Society]] |url=https://www.planetary.org/articles/12141551-change-2-imaging-of-toutatis |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203034955/https://www.planetary.org/articles/12141551-change-2-imaging-of-toutatis |archive-date=December 3, 2024}}</ref><ref name="IAU-NEOs"/>

The {{convert|980|m|ft|abbr=on}} Apollo asteroid [[162173 Ryugu]] was explored from June 2018<ref name="arrival">{{Cite news |first=Stephen |last=Clark |title=Japanese spacecraft reaches asteroid after three-and-a-half-year journey |date=June 28, 2018 |work=Spaceflight Now |url=https://spaceflightnow.com/2018/06/28/japanese-spacecraft-reaches-asteroid-after-three-and-a-half-year-journey/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231024060128/https://spaceflightnow.com/2018/06/28/japanese-spacecraft-reaches-asteroid-after-three-and-a-half-year-journey/ |archive-date=October 24, 2023}}</ref> until November 2019<ref name="Spacecom-Hayabusa2-2019">{{Cite news |first=Meghan |last=Bartels |title=Farewell, Ryugu! Japan's Hayabusa2 Probe Leaves Asteroid for Journey Home |date=November 13, 2019 |work=Space.com |url=https://www.space.com/hayabusa2-spacecraft-leaves-asteroid-ryugu.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231024064540/https://www.space.com/hayabusa2-spacecraft-leaves-asteroid-ryugu.html |archive-date=October 24, 2023}}</ref> by JAXA's ''[[Hayabusa2]]'' space probe, which returned a sample to Earth.<ref name="BBC-Hayabusa2">{{Cite news |first=Paul |last=Rincon |title=Hayabusa-2: Capsule with asteroid samples in 'perfect' shape |date=December 6, 2020 |work=BBC News |publisher=BBC |url=https://www.bbc.com/news/science-environment-55201662 |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231024064457/https://www.bbc.com/news/science-environment-55201662 |archive-date=October 24, 2023}}</ref> A second sample-return mission, NASA's ''[[OSIRIS-REx]]'' probe, targeted the {{convert|500|m|ft|abbr=on}} Apollo asteroid [[101955 Bennu]],<ref name="space-osiris-launch">{{cite news |first=Mike |last=Wall |title='Exactly Perfect'! NASA Hails Asteroid Sample-Return Mission's Launch |date=September 9, 2016 |work=Space.com |url=https://www.space.com/34020-nasa-hails-osiris-rex-asteroid-mission-launch.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231006005439/https://www.space.com/34020-nasa-hails-osiris-rex-asteroid-mission-launch.html |archive-date=October 6, 2023}}</ref> which, {{As of|2025|1|lc=y}}, has the third-highest cumulative Palermo scale rating (−1.40 for several close encounters between 2178 and 2290).<ref name="Current_Impact_Risks"/> On its journey to Bennu, the probe had searched unsuccessfully for Earth's Trojan asteroids,<ref>{{cite news |first1=Erin |last1=Morton |first2=Nancy |last2=Neal-Jones |title=NASA's OSIRIS-REx Begins Earth-Trojan Asteroid Search |date=February 9, 2017 |work=News |publisher=NASA |url=https://www.nasa.gov/centers-and-facilities/goddard/nasas-osiris-rex-begins-earth-trojan-asteroid-search/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203115428/https://www.nasa.gov/centers-and-facilities/goddard/nasas-osiris-rex-begins-earth-trojan-asteroid-search/ |archive-date=December 3, 2024}}</ref> entered into orbit around Bennu in December 2018, touched down on its surface in October 2020,<ref name="space-osiris-overview">{{cite news |first=Nola |last=Taylor Tillman |title=OSIRIS-REx: A complete guide to the asteroid-sampling mission |date=September 25, 2023 |work=[[Space.com]] |url=https://www.space.com/33776-osiris-rex.html |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240125154614/https://www.space.com/33776-osiris-rex.html |archive-date=January 25, 2024}}</ref> and was successful in returning samples to Earth three years later.<ref name="space-osiris-sample">{{cite news |first=John |last=Loeffer |title=NASA finally opens OSIRIS-REx asteroid sample canister after freeing stuck lid |date=January 23, 2024 |work=Space.com |url=https://www.space.com/nasa-osiris-rex-asteroid-sample-canister-open |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240125183741/https://www.space.com/nasa-osiris-rex-asteroid-sample-canister-open |archive-date=January 25, 2024}}</ref> China launched its own sample-return mission, ''[[Tianwen-2]]'', in May 2025, targeting Earth quasi-satellite {{mp|469219 Kamoʻoalewa|}} and returning samples to Earth in late 2027.<ref>{{cite web |title=Long March 3B/E. Tianwen 2 |work=[[NASASpaceFlight.com|Next Spaceflight]] |url=https://nextspaceflight.com/launches/details/4925 |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240901130100/https://nextspaceflight.com/launches/details/4925 |archive-date=September 1, 2024}}</ref>

After completing its mission to Bennu, the probe ''OSIRIS-REx'' was redirected towards 99942 Apophis, which it is planned to orbit from April 2029.<ref name="space-osiris-overview"/> After completing its exploration of 162173 Ryugu, the mission of the ''Hayabusa2'' space probe was extended, to include flybys of S-type Apollo asteroid [[98943 Torifune]] in July 2026 and fast-rotating Apollo asteroid {{mpl|1998 KY|26}} in July 2031.<ref>{{Cite conference |last1=Hirabayashi |first1=Masatoshi |last2=Yoshikawa |first2=Makoto |last3=Mimasu |first3=Yuya |last4=Tanaka |first4=Satoshi |last5=Saiki |first5=Takanao |last6=Nakazawa |first6=Satoru |last7=Tsuda |first7=Yuichi |last8=Tatsumi |first8=Eri |last9=Popescu |first9=Marcel |last10=Pravec |first10=Petr |last11=Urakawa |first11=Seitaro |last12=Yoshida |first12=Fumi |last13=Hirata |first13=Naru |last14=Kamata |first14=Shunichi |last15=Kitazato |first15=Kohei |display-authors=2 |date=February 15, 2023 |title=Hayabusa2#'s Exploration to Asteroids 2001 CC21 and 1998 KY26 Provides Key Insights Into Planetary Defense |url=https://ntrs.nasa.gov/citations/20230002153 |conference=8th IAA Planetary Defense Conference |location=Vienna, Austria |archive-url=https://web.archive.org/web/20240123201919/https://ntrs.nasa.gov/citations/20230002153 |archive-date=January 23, 2024 |url-status=live}}</ref> In 2025, JAXA plans to launch another probe, ''[[DESTINY+]]'', to explore Apollo asteroid {{mpl|3200 Phaethon|}}, the parent body of the [[Geminids|Geminid meteor shower]], during a flyby.<ref name="space-20231106">{{cite news |first=Andrew |last=Jones |title=Japan's mission to bizarre asteroid Phaethon delayed to 2025 |date=November 6, 2023 |work=Space.com |url=https://www.space.com/japan-destiny-mission-asteroid-phaethon-launch-delay |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101103731/https://www.space.com/japan-destiny-mission-asteroid-phaethon-launch-delay |archive-date=January 1, 2025}}</ref>

==== Asteroid deflection tests ====
[[File:DART-impact-SAAO-Lesedi-Mookodi.gif|thumb|Spread of the plume from the impact of the [[Double Asteroid Redirection Test|DART]] space probe on asteroid moon [[Dimorphos]] ([[SAAO]])]]

On September 26, 2022, NASA's ''[[Double Asteroid Redirection Test|DART]]'' spacecraft reached the system of {{mpl|65803 Didymos|}} and impacted the Apollo asteroid's moon [[Dimorphos]], in a test of a method of [[Asteroid impact avoidance|planetary defense]] against near-Earth objects.<ref name="NASA220927">{{cite news |first=Roxana |last=Bardan |title=NASA's DART Mission Hits Asteroid in First-Ever Planetary Defense Test |date=September 27, 2022 |work=Press Releases |publisher=NASA |url=https://www.nasa.gov/news-release/nasas-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250101142705/https://www.nasa.gov/news-release/nasas-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test/ |archive-date=January 1, 2025}}</ref> In addition to telescopes on or in orbit around the Earth, the impact was observed by the Italian mini-spacecraft or [[CubeSat]] ''LICIACube'', which separated from ''DART'' 15 days before impact.<ref name="NASA220927"/> The impact shortened the orbital period of Dimorphos around Didymos by 33 minutes, indicating that the moon's momentum change was 3.6 times the momentum of the impacting spacecraft, thus most of the change was due to the ejected material of the moon itself.<ref name="NASA221215">{{cite news |first=Jessica |last=Merzdorf |title=Early Results from NASA's DART Mission |date=December 15, 2022 |work=Press Releases |publisher=NASA |url=https://www.nasa.gov/solar-system/early-results-from-nasas-dart-mission/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250102153424/https://www.nasa.gov/solar-system/early-results-from-nasas-dart-mission/ |archive-date=January 2, 2025}}</ref>

In October 2024, ESA launched the spacecraft ''[[Hera (space mission)|Hera]]'', which is to enter orbit around Didymos in December 2026, to study the consequences of the DART impact.<ref>{{cite web |title=Hera |publisher=ESA |url=https://www.esa.int/Space_Safety/Hera |access-date=December 31, 2024 |url-status=live |archive-url=https://web.archive.org/web/20241231085805/https://www.esa.int/Space_Safety/Hera |archive-date=December 31, 2024}}</ref> China plans to launch its own pair of asteroid deflection and observation probes in 2027, which are to target {{convert|30|m|ft|abbr=on}} Aten asteroid {{mpl|2015 XF|261}}.<ref>{{cite web |first1=Andrew |last1=Jones |title=China targets its first planetary defense test mission |date=July 2, 2024 |publisher=The Planetary Society |url=https://www.planetary.org/articles/china-targets-its-first-planetary-defense-test-mission |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241008065834/https://www.planetary.org/articles/china-targets-its-first-planetary-defense-test-mission |archive-date=October 8, 2024}}</ref>

==== Space mining ====

From the 2000s, there were plans for the commercial exploitation of near-Earth asteroids, either through the use of robots or even by sending private commercial astronauts to act as space miners, but few of these plans were pursued.<ref name="Forbes210831">{{Cite news |last=Dorminey |first=Bruce |title=Does Commercial Asteroid Mining Still Have A Future? |date=August 31, 2021 |work=[[Forbes]] |url=https://www.forbes.com/sites/brucedorminey/2021/08/31/does-commercial-asteroid-mining-still-have-a-future/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240804082359/https://www.forbes.com/sites/brucedorminey/2021/08/31/does-commercial-asteroid-mining-still-have-a-future/ |archive-date=August 4, 2024}}</ref>

In April 2012, the company [[Planetary Resources]] announced its plans to [[Asteroid mining|mine asteroids]] commercially. In a first phase, the company reviewed data and selected potential targets among NEAs. In a second phase, space probes would be sent to the selected NEAs; mining spacecraft would be sent in a third phase.<ref name="ST-AsteroidMining">{{cite news |first=Kelly |last=Beatty |title=Asteroid Mining for Fun and Profit |date=April 24, 2012 |work=Sky & Telescope |url=http://www.skyandtelescope.com/astronomy-news/asteroid-mining-forfunandprofit/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20240912123200/https://skyandtelescope.org/astronomy-news/asteroid-mining-forfunandprofit/ |archive-date=September 12, 2024}}</ref> Planetary Resources launched two testbed satellites in April 2015<ref name="Arkyd6LeftBuilding"/> and January 2018,<ref>{{cite news |title=Planetary Resources Launches Latest Spacecraft in Advance of Space Resource Exploration Mission |date=January 12, 2018 |work=News |publisher=Planetary Resources |url=https://www.planetaryresources.com/2018/01/planetary-resources-launches-latest-spacecraft-in-advance-of-space-resource-exploration-mission/ |access-date=January 13, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20180113093243/https://www.planetaryresources.com/2018/01/planetary-resources-launches-latest-spacecraft-in-advance-of-space-resource-exploration-mission/ |archive-date=January 13, 2018}}</ref> and the first prospecting satellite for the second phase was planned for a 2020 launch prior to the company closing and its assets purchased by ConsenSys Space in 2018.<ref name="Arkyd6LeftBuilding">{{cite news |first=Alan |last=Boyle |title=Planetary Resources' Arkyd-6 prototype imaging satellite has left the building |date=November 13, 2017 |work=[[GeekWire]] |url=https://www.geekwire.com/2017/planetary-resources-arkyd-6-prototype-imaging-satellite-left-building/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20171114080201/https://www.geekwire.com/2017/planetary-resources-arkyd-6-prototype-imaging-satellite-left-building/ |archive-date=November 14, 2017}}</ref><ref name="oneyearsinceplanetaryresources">{{cite news |first=Alan |last=Boyle |title=One year after Planetary Resource faded into history, space mining retails its appeal |date=November 4, 2019 |work=GeekWire |url=https://www.geekwire.com/2019/one-year-planetary-resources-faded-history-space-mining-retains-appeal/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231014085126/https://www.geekwire.com/2019/one-year-planetary-resources-faded-history-space-mining-retains-appeal/ |archive-date=October 14, 2023}}</ref>

Another American company established with the goal of space mining, [[AstroForge]], launched the probe ''Odin'' (formerly ''Brokkr-2'') on February 26, 2025, to perform a flyby of asteroid {{mpl|2022 OB|5}}, but the probe showed technical problems.<ref name="Odin-launch-problems">{{cite news |first=Tariq |last=Malik |title='I think we all know that hope is fading.' Private Odin asteroid probe is tumbling in space |date=March 1, 2025 |work=Space.com |url=https://www.space.com/space-exploration/private-spaceflight/i-think-we-all-know-that-hope-is-fading-private-odin-asteroid-probe-is-tumbling-in-space |access-date=March 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20250301230617/https://www.space.com/space-exploration/private-spaceflight/i-think-we-all-know-that-hope-is-fading-private-odin-asteroid-probe-is-tumbling-in-space |archive-date=March 1, 2025}}</ref> The  goal of the mission was to confirm if {{mp|2022 OB|5}} is a metal-rich [[M-type asteroid]].<ref>{{Cite news |first=Alex |last=Knapp |title=This Asteroid Mining Startup Is Ready To Launch The First-Ever Commercial Deep Space Mission |date=October 18, 2023 |work=Forbes |url=https://www.forbes.com/sites/alexknapp/2023/10/18/this-asteroid-mining-startup-is-ready-to-launch-the-first-ever-commercial-deep-space-mission/ |access-date=January 3, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241123112719/https://www.forbes.com/sites/alexknapp/2023/10/18/this-asteroid-mining-startup-is-ready-to-launch-the-first-ever-commercial-deep-space-mission/ |archive-date=November 23, 2024}}</ref> Regardless of the success of ''Odin'', AstroForge plans  to follow it up a year later with the probe ''Vestri'', which is to land on the same asteroid.<ref name="Odin-launch-problems"/>

=== Missions to NECs ===
[[File:67P Churyumov-Gerasimenko - Rosetta (32755885495).png|thumb|Nucleus of comet [[67P/Churyumov–Gerasimenko]] as seen by ESA's ''[[Rosetta (spacecraft)|Rosetta]]'' probe]]

The first near-Earth comet visited by a space probe was [[21P/Giacobini–Zinner]] in 1985, when the NASA/ESA probe ''[[International Cometary Explorer]]'' (''ICE'') passed through its coma. In March 1986, ICE, along with [[Soviet Union|Soviet]] probes ''[[Vega 1]]'' and ''[[Vega 2]]'', [[Institute of Space and Astronautical Science|ISAS]] probes ''[[Sakigake]]'' and ''[[Suisei (spacecraft)|Suisei]]'' and ESA probe ''[[Giotto (spacecraft)|Giotto]]'' flew by the nucleus of Halley's Comet. In 1992, ''Giotto'' also visited another NEC, [[26P/Grigg–Skjellerup]].<ref name="TaskForceReport"/>

In November 2010, after completing its primary mission to non-near-Earth comet [[Tempel 1]], the NASA probe ''[[Deep Impact (spacecraft)|Deep Impact]]'' flew by the near-Earth comet [[103P/Hartley]].<ref name="DeepImpactHartley">{{Cite news |title=Mr. Hartley's Amazing Comet |first=Kelly |last=Beatty |date=November 4, 2010 |work=[[Sky & Telescope]] |url=https://skyandtelescope.org/astronomy-news/mr-hartleys-amazing-comet/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20231020025244/https://skyandtelescope.org/astronomy-news/mr-hartleys-amazing-comet/ |archive-date=October 20, 2023}}</ref>

In August 2014, ESA probe ''Rosetta'' began orbiting near-Earth comet [[67P/Churyumov–Gerasimenko]], while its lander ''[[Philae (spacecraft)|Philae]]'' landed on its surface in November 2014. After the end of its mission, Rosetta was crashed into the comet's surface in 2016.<ref name="newsci20160930">{{cite news |first=Jacob |last=Aron |title=Rosetta lands on 67P in grand finale to two year comet mission |date=September 30, 2016 |work=[[New Scientist]] |url=https://www.newscientist.com/article/2107585-rosetta-lands-on-67p-in-grand-finale-to-two-year-comet-mission/ |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20241203014854/https://www.newscientist.com/article/2107585-rosetta-lands-on-67p-in-grand-finale-to-two-year-comet-mission/ |archive-date=December 3, 2024}}</ref>
{{clear}}

== See also ==
{{div col|colwidth=20em}}
* [[Asteroid capture]]
* [[Asteroid Day]]
* [[Asteroid Redirect Mission]]
* [[Claimed moons of Earth]]
* [[EURONEAR]]
* [[Interstellar object|Interstellar interloper]]
* [[List of Earth-crossing asteroids]]
* [[List of impact craters on Earth]]
* [[NEOShield]] 
* [[Orbit@home]]
{{div col end}}

== References ==
{{reflist|25em|refs=

<ref name=Helsinki>{{cite web
  |title       = Asteroid impact threat estimates improved for the Earth and the Moon {{!}} University of Helsinki
  |url         = https://www.helsinki.fi/en/news/space/asteroid-impact-threat-estimates-improved-earth-and-moon
  |website     = www.helsinki.fi
  |language    = en
  |date        = 2025-04-02
  |access-date =2025-04-02}}</ref>

<ref name="BillGray">{{cite web
 |title        = Risk Corridor for Gibbous Moon
 |url          = https://www.projectpluto.com/temp/yr4/moon.png
 |first        = Bill
 |last         = Gray
 |work         = Find_Orb
 |access-date  = 18 February 2025
 |archive-date = 10 February 2025
 |archive-url  = https://web.archive.org/web/20250210080345/https://www.projectpluto.com/temp/yr4/moon.png
 |url-status   = live}}</ref>

<ref name="pia14734">{{cite web
  |title       = WISE Revises Numbers of Asteroids Near Earth
  |date        = September 29, 2011
  |publisher   = NASA/JPL
  |url         = https://www.jpl.nasa.gov/images/pia14734-wise-revises-numbers-of-asteroids-near-earth
  |access-date = January 2, 2025
  |url-status  = live
  |archive-url = https://web.archive.org/web/20240127112654/https://www.jpl.nasa.gov/images/pia14734-wise-revises-numbers-of-asteroids-near-earth
  |archive-date= January 27, 2024}}</ref>

<ref name="JPL-SSD-NEA">{{cite web
  |title      = JPL Small-Body Database Search Engine. Constraints: asteroids and NEOs
  |date       = January 1, 2025
  |publisher  = [[JPL Small-Body Database]]
  |url        = https://ssd.jpl.nasa.gov/tools/sbdb_query.html
  |access-date = January 1, 2025
  |url-status  = live
  |archive-url = https://web.archive.org/web/20250101171802/https://ssd.jpl.nasa.gov/tools/sbdb_query.html
  |archive-date = January 1, 2025}}</ref>

<ref name="closest-NEA">{{cite web
  |title      = Closest Approaches to the Earth by Minor Planets
  |date       = May 16, 2019
  |publisher  = IAU/MPC
  |url        = http://www.minorplanetcenter.net/iau/Closest.html
  |access-date = January 1, 2025
  |url-status =live
  |archive-url = https://web.archive.org/web/20241222014339/https://minorplanetcenter.net//iau/lists/Closest.html
  |archive-date = December 22, 2024}}</ref>

<ref name="closest-NEC">{{cite web
  |title      = Closest Approaches to the Earth by Comets
  |date       = May 16, 2019
  |publisher  = IAU/MPC
  |url        = https://www.minorplanetcenter.net/iau/lists/ClosestComets.html
  |access-date = January 1, 2025
  |url-status =live
  |archive-url = https://web.archive.org/web/20240807145120/https://www.minorplanetcenter.net/iau/lists/ClosestComets.html
  |archive-date = August 7, 2024}}</ref>

<ref name="Earth-impact">{{cite web
  |first1     = Robert
  |last1      = Marcus
  |first2     = H. Jay
  |last2      = Melosh
  |first3     = Gareth
  |last3      = Collins
  |name-list-style = amp
  |title      = Earth Impact Effects Program
  |date       = 2010
  |publisher  = Imperial College London / Purdue University
  |url        = https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/
  |access-date = January 2, 2025
  |url-status = live
  |archive-url = https://web.archive.org/web/20240124034305/https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/
  |archive-date = January 24, 2024}} (solution using 2600&nbsp;kg/m^3, 17&nbsp;km/s, 45 degrees)</ref>

<ref name="IAU-NEOs">{{cite web
  |title      = Near Earth Objects
  |publisher  = [[International Astronomical Union|IAU]]
  |url        = https://www.iau.org/public/themes/neo/
  |access-date = January 2, 2025
  |url-status = live
  |archive-url = https://web.archive.org/web/20241217212810/https://www.iau.org/public/themes/neo/
  |archive-date = December 17, 2024}}</ref>

<ref name="neo-jpl-stats">{{cite web
  |title      = Discovery Statistics – Cumulative Totals
  |date       = December 30, 2024
  |publisher  = NASA/JPL CNEOS
  |url        = https://cneos.jpl.nasa.gov/stats/totals.html
  |access-date = January 1, 2025
  |url-status = live
  |archive-url = https://web.archive.org/web/20250101175111/https://cneos.jpl.nasa.gov/stats/totals.html
  |archive-date = January 1, 2025}}</ref>
<!-- The above source, which is updated every few days, also contains diagrams which are the source of four Wikimedia files embedded in this article. The latter should be updated (overwritten) annually, using the end-of-the-year version saved from the source at the start of the next year, simultaneously with the stats on this page from this same source -->

<ref name="Current_Impact_Risks">{{cite web
  |title      = Sentry Risk Table
  |url        = https://cneos.jpl.nasa.gov/sentry/
  |publisher  = NASA/JPL CNEOS
  |access-date = March 2, 2025
  |url-status = live
  |archive-url = https://web.archive.org/web/20250302170007/https://cneos.jpl.nasa.gov/sentry/
  |archive-date = March 2, 2025}}</ref>

<ref name="h">{{cite web
  |title      = Asteroid Size Estimator
  |publisher  = NASA/JPL CNEOS
  |url        = https://cneos.jpl.nasa.gov/tools/ast_size_est.html
  |access-date = January 1, 2025
  |url-status = live
  |archive-url = https://web.archive.org/web/20250101175034/https://cneos.jpl.nasa.gov/tools/ast_size_est.html
  |archive-date = January 1, 2025}}</ref>

}} <!-- end of reflist -->

==External links==
{{Commons category|Near-Earth objects}}
* [http://cneos.jpl.nasa.gov/ Center for Near Earth Object Studies (CNEOS)] – [[Jet Propulsion Laboratory]], [[NASA]]
* [http://www.brera.mi.astro.it/sormano/teca.html Table of Asteroids Next Closest Approaches to the Earth] – Sormano Astronomical Observatory
* [http://smallbodies.ru/en/ Catalogue of the Solar System Small Bodies Orbital Evolution] – Samara State Technical University

; Minor Planet Center
* [http://www.minorplanetcenter.net/iau/NEO/toconfirm_tabular.html The NEO Confirmation Page]
* {{YouTube|id=Ar_h-zAccsY|title=Minor Planet Center: Asteroid Hazards, Part 2: ''The Challenge of Detection''}} {{small|(min. 7:14)}}
* {{YouTube|id=8M_27st1ZCI|title=Minor Planet Center: Asteroid Hazards, Part 3: ''Finding the Path''}} {{small|(min. 5:38)}}

{{Planetary defense}}
{{Modern impact events}}
{{Asteroids}}
{{Small Solar System bodies}}
{{Solar System}}
{{Portal bar|Solar System|Astronomy|Spaceflight|Outer space|Science}}
{{Authority control}}

{{DEFAULTSORT:Near-Earth Object}}
[[Category:Articles containing video clips]]
[[Category:Near-Earth objects| ]]
[[Category:Planetary defense]]
[[Category:Space hazards]]
[[Category:Solar System]]