Editing Near-Earth object (section)

{{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 = Asteroid2006DP14.jpg
| caption1 = Radar image of {{mpl|(388188) 2006 DP|14}} recorded by a [[NASA Deep Space Network|DSN]] antenna
| 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}} 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"/>