Editing Asteroid (section)

=== Near-Earth asteroids ===
{{Main|Near-Earth object#Near-Earth asteroids|l1=Near-Earth asteroids}}

Near-Earth asteroids, or NEAs, are asteroids that have orbits that pass close to that of Earth. Asteroids that actually cross Earth's orbital path are known as ''Earth-crossers''. {{As of|2022|04}}, a total of 28,772&nbsp;near-Earth asteroids were known; 878 have a diameter of one kilometer or larger.<ref name=nasa_neo>{{cite web |title=Discovery Statistics |url=https://cneos.jpl.nasa.gov/stats/totals.html |website=CNEOS |access-date=14 April 2022}}</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? |author=D.F. Lupishko |author2=M. di Martino |author3=T.A. 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|2021|10|df=US}}, there were 85 NEAs known to have at least one moon, including three known to have two moons.<ref>{{cite web |title=Asteroids with Satellites |publisher=Johnston's Archive |url=http://www.johnstonsarchive.net/astro/asteroidmoons.html |access-date=2018-03-17}}</ref> The asteroid [[3122 Florence]], one of the largest potentially hazardous asteroids 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 |author1=Lance Benner |author2=Shantanu Naidu |author3=Marina Brozovic |author4=Paul Chodas |title=Radar Reveals Two Moons Orbiting Asteroid Florence |work=News |publisher=NASA/JPL CNEOS |date=1 September 2017 |url=https://cneos.jpl.nasa.gov/news/news199.html |access-date=2018-01-19 |url-status=live |archive-url=https://web.archive.org/web/20170903060914/https://cneos.jpl.nasa.gov/news/news199.html |archive-date=2017-09-03 }}</ref>

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="NEO-groups">{{cite web |title=NEO Basics. NEO Groups |publisher=NASA/JPL CNEOS |url=http://cneos.jpl.nasa.gov/neo/groups.html |access-date=2017-11-09}}</ref><ref name="MorbidelliAstIII">{{cite book |url=http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |contribution=Origin and Evolution of Near-Earth Objects |first1=Alessandro |last1=Morbidelli |first2=William F. Jr. |last2=Bottke |first3=Christiane |last3=Froeschlé |first4=Patrick |last4=Michel |title=Asteroids III |editor=W. F. Bottke Jr. |editor2=A. Cellino |editor3=P. Paolicchi |editor4=R. P. Binzel |pages=409–422 |date=January 2002 |doi=10.2307/j.ctv1v7zdn4.33 |bibcode=2002aste.book..409M |access-date=2017-11-09 |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=2017-08-09 }}</ref>
* 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=1 August 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>
* 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.