Editing Near-Earth object (section)

== 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>

{{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|mi/s|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=Emel'Yanenko |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 |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]]. 10.7&nbsp;kg 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}}

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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 |doi=10.1016/j.icarus.2021.114452 |bibcode=2021Icar..36514452H}}</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"/>