Aten asteroid: Difference between revisions
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{{Short description|Group of near-Earth asteroids}} |
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The '''Aten asteroids''' are a group of [[near-Earth asteroid]]s, named after the first of the group to be discovered ([[2062 Aten]], discovered [[January 7]] [[1976]] by [[Eleanor F. Helin]]). They have [[semi-major axis|semi-major axes]] of less than one [[astronomical unit]], placing them inside the orbit of Earth. |
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[[File:Neo orbit types.jpg|thumb|upright=2.4|Common orbital subgroups of [[Near-Earth Object]]s (NEOs)]] |
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The '''Aten asteroids''' are a [[List of minor-planet groups|dynamical group]] of [[asteroid]]s whose orbits bring them into [[Near-Earth object|proximity with Earth]]. By definition, Atens are [[Earth-crossing asteroid]]s {{nowrap|([[Semi-major axis|a]] < 1.0 [[Astronomical unit|AU]] and [[Aphelion|Q]] > 0.983 AU)}}.<ref name="NEO-Basics" /> The group is named after [[2062 Aten]], the first of its kind, discovered on 7 January 1976 by American astronomer [[Eleanor Helin]] at [[Palomar Observatory]]. As of October 2024, 2,860 Atens have been discovered, of which 266 are numbered, 14 are named, and 191 are classified as [[potentially hazardous asteroids]].<ref>{{cite web |title=Small-Body Database Query |url=https://ssd.jpl.nasa.gov/tools/sbdb_query.html#!#results |website=Solar System Dynamics - Jet Propulsion Laboratory |publisher=NASA - California Institute of Technology |access-date=2024-10-10}}</ref><ref name="Aten list" /<ref name="MPC-Aten" /><ref name="neo-jpl-stats" /> |
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Nearly all known Aten asteroids have their [[aphelion]] greater than one AU. Those that have their aphelion entirely within the [[Earth]]'s orbit are known as [[Apohele asteroid]]s. As of May [[2004]] there are only two known Apoheles: {{mpl|2003 CP|20}} and {{mpl|2004 JG|6}}. |
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== Description == |
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The smallest semi-major axis is that of {{mpl|(66391) 1999 KW|4}}, at 0.642 AU (its [[eccentricity (orbit)|eccentricity]] of 0.688 takes it from a perihelion of 0.200 AU —well within [[Mercury (planet)|Mercury]]'s orbit!— to an aphelion of 1.084 AU), although {{mp|2004 JG|6}} seems to have an even smaller one (0.635 AU; eccentricity 0.532 ranging from 0.297 to 0.973 AU —enough to cross [[Venus (planet)|Venus]]' orbit but not Mercury's). |
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{{See also|List of Aten asteroids|Category:Aten asteroids}} |
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Aten asteroids are defined by having a [[semi-major axis]] (a) of less than 1.0 [[astronomical unit]] (AU), the roughly average distance from the [[Earth]] to the [[Sun]]. They also have an [[aphelion]] (Q; furthest distance from the Sun) greater than 0.983 AU.<ref name="NEO-Basics" /> This defines them as [[Earth-crossing asteroid]]s as the orbit of Earth varies between 0.983 and 1.017 AU. |
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For a brief time near the end of [[2004]], the asteroid [[99942 Apophis]] (then known only by its [[provisional designation]] {{mp|2004 MN|4}}) appeared to pose a threat of causing an Earth [[impact event]] in [[2029]], but earlier observations were found that eliminated that possibility, although a very small possibility still exists for the years [[2035]] and [[2036]]. |
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Asteroids' orbits can be highly eccentric. Nearly all known Aten asteroids have an [[aphelion]] greater than 1 AU. Observation of objects [[inferior and superior planets|inferior]] to the Earth's orbit is difficult, and this difficulty may contribute to [[sampling bias]] in the apparent preponderance of eccentric Atens. Aten asteroids account for only about 7.4% of the known [[near-Earth Object|near-Earth asteroid population]].<ref name="neo-jpl-stats" /> Many more [[List of Apollo asteroids|Apollo-class asteroids]] are known than Aten-class asteroids, possibly because of the sampling bias. |
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==Related topics== |
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The shortest semi-major axis for any known Aten asteroid is 0.580 AU, for object {{mp|2016 XK|24}}.<ref name="MPC-Aten" /> The Aten asteroid with the smallest known perihelion is also the one with the highest known [[eccentricity (orbit)|eccentricity]]: {{mpl|(137924) 2000 BD|19}} has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within [[Mercury (planet)|Mercury]]'s orbit, to an aphelion of 1.66 AU, which is greater than the semi-major axis of [[Mars]] (1.53 AU). |
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==External links== |
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* [http://cfa-www.harvard.edu/iau/lists/Atens.html List of Aten Minor Planets] |
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== NEO types== |
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{{MinorPlanets_Footer}} |
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{| class="wikitable" style="width: 330px; text-align: center;" |
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|+ Definition of [[Near-Earth object|NEO]] subgroups in [[Astronomical unit|AU]] <ref name="NEO-Basics" /> |
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|- |
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! Group !! [[Perihelion|q]] !! [[Semi-major axis|a]] !! [[Aphelion|Q]] !! [[Earth-crossing asteroid|ECA]] |
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|- |
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| align=left | [[Amor asteroid|Amors]] || > 1.017 || >1.0 || – || {{n}} |
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|- |
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| align=left | [[Apollo asteroid|Apollos]] || < 1.017 || >1.0 || – || {{y}} |
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|- |
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| align=left | '''Atens''' || – || <1.0 || > 0.983 || {{y}} |
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|- |
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| align=left | [[Atira asteroid|Atiras]] || – || <1.0 || < 0.983 || {{n}} |
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|- |
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! colspan=5 style="font-size: small; font-weight: normal; text-align: left;" | For all NEOs q is < 1.3 AU; The orbit of [[Earth]] varies between 0.983 and 1.017 AU |
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|} |
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== See also == |
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[[Category:Aten asteroids|*]] |
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* [[Alinda asteroid]] |
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* [[Apollo asteroid]] |
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* [[Atira asteroid]] |
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== References == |
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[[ca:Asteroides Aton]] |
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{{reflist|30em|refs= |
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[[cs:Atenova skupina]] |
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[[da:Aten-asteroide]] |
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<ref name="MPC-Aten">{{cite web |
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[[fr:Aten]] |
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|title = List Of Aten Minor Planets (by perihelion distance) |
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[[zh:阿登型小行星]] |
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|publisher = Minor Planet Center |
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|date = 17 May 2017 |
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|url = https://minorplanetcenter.net/iau/lists/t_atens.html |
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|access-date = 17 May 2017}}</ref> |
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<ref name="NEO-Basics">{{cite web |
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|title = NEO Basics |
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|publisher = NASA/JPL CNEOS |
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|url = https://cneos.jpl.nasa.gov/about/neo_groups.html |
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|access-date = 17 May 2018}}</ref> |
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<!-- unused <ref name="Aten list">{{cite web |
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|title = JPL Small-Body Database Search Engine |
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|publisher = NASA/JPL |
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|url = https://ssd.jpl.nasa.gov/sbdb_query.cgi#x |
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|access-date = 10 October 2024}}</ref> --> |
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<ref name="neo-jpl-stats">{{cite web |
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|title = Discovery Statistics – Cumulative Totals |
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|publisher = NASA/JPL CNEOS |
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|url = https://cneos.jpl.nasa.gov/stats/totals.html |
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|date = 10 October 2024 |
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|access-date = 10 October 2024}}</ref> |
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}} <!-- end reflist --> |
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{{Use dmy dates|date=October 2019}} |
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{{Asteroids}} |
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{{Small Solar System bodies}} |
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{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}} |
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Latest revision as of 17:41, 10 October 2024
The Aten asteroids are a dynamical group of asteroids whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids (a < 1.0 AU and Q > 0.983 AU).[1] The group is named after 2062 Aten, the first of its kind, discovered on 7 January 1976 by American astronomer Eleanor Helin at Palomar Observatory. As of October 2024, 2,860 Atens have been discovered, of which 266 are numbered, 14 are named, and 191 are classified as potentially hazardous asteroids.[2][3][4]
Description
[edit]Aten asteroids are defined by having a semi-major axis (a) of less than 1.0 astronomical unit (AU), the roughly average distance from the Earth to the Sun. They also have an aphelion (Q; furthest distance from the Sun) greater than 0.983 AU.[1] This defines them as Earth-crossing asteroids as the orbit of Earth varies between 0.983 and 1.017 AU.
Asteroids' orbits can be highly eccentric. Nearly all known Aten asteroids have an aphelion greater than 1 AU. Observation of objects inferior to the Earth's orbit is difficult, and this difficulty may contribute to sampling bias in the apparent preponderance of eccentric Atens. Aten asteroids account for only about 7.4% of the known near-Earth asteroid population.[4] Many more Apollo-class asteroids are known than Aten-class asteroids, possibly because of the sampling bias.
The shortest semi-major axis for any known Aten asteroid is 0.580 AU, for object 2016 XK24.[3] The Aten asteroid with the smallest known perihelion is also the one with the highest known eccentricity: (137924) 2000 BD19 has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within Mercury's orbit, to an aphelion of 1.66 AU, which is greater than the semi-major axis of Mars (1.53 AU).
NEO types
[edit]| Group | q | a | Q | ECA |
|---|---|---|---|---|
| Amors | > 1.017 | >1.0 | – | 
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| Apollos | < 1.017 | >1.0 | – | 
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| Atens | – | <1.0 | > 0.983 |
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| Atiras | – | <1.0 | < 0.983 |
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| For all NEOs q is < 1.3 AU; The orbit of Earth varies between 0.983 and 1.017 AU | ||||
See also
[edit]References
[edit]- ^ a b c "NEO Basics". NASA/JPL CNEOS. Retrieved 17 May 2018.
- ^ "Small-Body Database Query". Solar System Dynamics - Jet Propulsion Laboratory. NASA - California Institute of Technology. Retrieved 10 October 2024.
- ^ a b "List Of Aten Minor Planets (by perihelion distance)". Minor Planet Center. 17 May 2017. Retrieved 17 May 2017.
- ^ a b "Discovery Statistics – Cumulative Totals". NASA/JPL CNEOS. 10 October 2024. Retrieved 10 October 2024.
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