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{{Short description|Group of near-Earth asteroids}}
[[da:Aten-asteroide]]
[[File:Neo orbit types.jpg|thumb|upright=2.4|Common orbital subgroups of [[Near-Earth Object]]s (NEOs)]]
[[de:Aten-Typ]]


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]]&thinsp;&lt;&thinsp;1.0&nbsp;[[Astronomical unit|AU]] and [[Aphelion|Q]]&thinsp;&gt;&thinsp;0.983&nbsp;AU)}}.<ref name="NEO-Basics" /> The group is named after [[2062&nbsp;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" />
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 E. F. Helin). They have average orbital diameters closer than one astronomical unit (AU, the distance from the Earth to the Sun), placing them inside the orbit of Earth.


== Description ==
⚫
Well-known Aten asteroids include:
{{See also|List of Aten asteroids|Category:Aten asteroids}}


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&nbsp;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&nbsp;AU.
{|

! Name !! Year !! Discoverer
Asteroids' orbits can be highly eccentric. Nearly all known Aten asteroids have an [[aphelion]] greater than 1&nbsp;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.
| [[2004 FH]] || 2004 || [[LINEAR]]

The shortest semi-major axis for any known Aten asteroid is 0.580&nbsp;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&nbsp;AU, well within [[Mercury (planet)|Mercury]]'s orbit, to an aphelion of 1.66&nbsp;AU, which is greater than the semi-major axis of [[Mars]] (1.53 AU).

== NEO types==
{| class="wikitable" style="width: 330px; text-align: center;"
|+ Definition of [[Near-Earth object|NEO]] subgroups in [[Astronomical unit|AU]]&thinsp;<ref name="NEO-Basics" />
|-
|-
! Group !! [[Perihelion|q]] !! [[Semi-major axis|a]] !! [[Aphelion|Q]] !! [[Earth-crossing asteroid|ECA]]
| [[5381 Sekhmet]] || 1991 || [[Carolyn Shoemaker]]
|-
|-
| [[3753 Cruithne]] || 1986 || [[J. D. Waldron]]
| align=left | [[Amor asteroid|Amors]] || > 1.017 || >1.0 || – || {{n}}
|-
|-
| align=left | [[Apollo asteroid|Apollos]] || < 1.017 || >1.0 || – || {{y}}
| [[3554 Amun]] || 1986 || [[Carolyn Shoemaker]], [[Eugene Shoemaker]]
|-
|-
| [[3362 Khufu]] || 1984 || [[R. S. Dunbar]], [[M. A. Barucci]]
| align=left | '''Atens''' || – || <1.0 || > 0.983 || {{y}}
|-
|-
| align=left | [[Atira asteroid|Atiras]] || – || <1.0 || < 0.983 || {{n}}
| [[2340 Hathor]] || 1976 || [[Charles Kowal]]
|-
|-
! colspan=5 style="font-size: small; font-weight: normal; text-align: left;" | For all NEOs q is < 1.3&nbsp;AU; The orbit of [[Earth]] varies between 0.983 and 1.017&nbsp;AU
| [[2100 Ra-Shalom]] || 1978 || [[E. F. Helin]]
|-
|}

| [[2062 Aten]] || 1976 || [[E. F. Helin]]
== See also ==
|}
* [[Alinda asteroid]]
* [[Amor asteroid]]
* [[Apollo asteroid]]
* [[Atira asteroid]]
* [[List of minor planets]]

== References ==
{{reflist|30em|refs=

<ref name="MPC-Aten">{{cite web
|title = List Of Aten Minor Planets (by perihelion distance)
|publisher = Minor Planet Center
|date = 17 May 2017
|url = https://minorplanetcenter.net/iau/lists/t_atens.html
|access-date = 17 May 2017}}</ref>

<ref name="NEO-Basics">{{cite web
|title = NEO Basics
|publisher = NASA/JPL CNEOS
|url = https://cneos.jpl.nasa.gov/about/neo_groups.html
|access-date = 17 May 2018}}</ref>

<!-- unused <ref name="Aten list">{{cite web
|title = JPL Small-Body Database Search Engine
|publisher = NASA/JPL
|url = https://ssd.jpl.nasa.gov/sbdb_query.cgi#x
|access-date = 10 October 2024}}</ref> -->

<ref name="neo-jpl-stats">{{cite web
|title = Discovery Statistics – Cumulative Totals
|publisher = NASA/JPL CNEOS
|url = https://cneos.jpl.nasa.gov/stats/totals.html
|date = 10 October 2024
|access-date = 10 October 2024}}</ref>

}} <!-- end reflist -->

{{Use dmy dates|date=October 2019}}
{{Asteroids}}
{{Small Solar System bodies}}
{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}


⚫
[[Category:Aten asteroids|*]]
==External links==
* [http://cfa-www.harvard.edu/iau/lists/Atens.html List of Aten Minor Planets]

Latest revision as of 17:41, 10 October 2024

Common orbital subgroups of Near-Earth Objects (NEOs)

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]
See also: List of Aten asteroids and Category:Aten asteroids

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]
Definition of NEO subgroups in AU [1]
Group q a Q ECA
Amors > 1.017 >1.0 – Red XN
Apollos < 1.017 >1.0 – Green tickY
Atens – <1.0 > 0.983 Green tickY
Atiras – <1.0 < 0.983 Red XN
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]
  1. ^ a b c "NEO Basics". NASA/JPL CNEOS. Retrieved 17 May 2018.
  2. ^ "Small-Body Database Query". Solar System Dynamics - Jet Propulsion Laboratory. NASA - California Institute of Technology. Retrieved 10 October 2024.
  3. ^ a b "List Of Aten Minor Planets (by perihelion distance)". Minor Planet Center. 17 May 2017. Retrieved 17 May 2017.
  4. ^ a b "Discovery Statistics – Cumulative Totals". NASA/JPL CNEOS. 10 October 2024. Retrieved 10 October 2024.

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