Atira asteroid

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Template:Short description

File:Neo orbit types.jpg
Common orbital subgroups of Near-Earth Objects (NEOs)

Atira asteroids Template:IPAc-en or Apohele asteroids, also known as interior-Earth objects (IEOs), are Near-Earth objects whose orbits are entirely confined within Earth's orbit;[1] that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's perihelion (nearest point to the Sun), which is 0.983 astronomical units (AU). Atira asteroids are by far the least numerous group of near-Earth objects, compared to the more populous Aten, Apollo and Amor asteroids.[2]

History

Naming

There is no official name for the class commonly referred as Atira asteroids. The term "Apohele asteroids" was proposed by the discoverers of Template:Mpl,[3] after the Hawaiian word for orbit, from apo Script error: No such module "IPA". 'circle' and hele Script error: No such module "IPA". 'to go'.[4] This was suggested partly because of its similarity to the words aphelion (apoapsis) and helios.Template:Efn Other authors adopted the designation "Inner Earth Objects" (IEOs).[5] Following the general practice to name a new class of asteroids for the first recognized member of that class, which in this case was 163693 Atira, the designation of "Atira asteroids" was largely adopted by the scientific community, including by NASA.[6][1]

Discovery and observation

Their location inside the Earth's orbit makes Atiras very difficult to observe, as from Earth's perspective they are close to the Sun and therefore 'drowned out' by the Sun's overpowering light.[7] This means that Atiras can usually only be seen during twilight.[7] The first documented twilight searches for asteroids inside Earth's orbit were performed by astronomer Robert Trumpler over the early 20th century, but he failed to find any.[7]

The first confirmed Atira asteroid was 163693 Atira in 2003, discovered by the Lincoln Laboratory Near Earth Asteroid Research Team.[8] since January 2025Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters"., there are 34 known Atiras, two of which are named, nine of which have received a numbered designation, and seven of which are potentially hazardous objects.[2][9][10]

Origins

Most Atira asteroids originated in the asteroid belt and were driven to their current locations as a result of gravitational perturbation, as well as other causes such as the Yarkovsky effect.[7] A number of known Atiras could be fragments or former moons of larger Atiras as they exhibit an unusually high level of orbital correlation.[11]

Orbits

Atiras do not cross Earth's orbit and are not immediate impact event threats, but their orbits may be perturbed outward by a close approach to either Mercury or Venus and become Earth-crossing asteroids in the future. The dynamics of many Atira asteroids resemble the one induced by the Kozai-Lidov mechanism,Template:Efn which contributes to enhanced long-term orbital stability, since there is no libration of the perihelion.[12][13]

Exploration

A 2017 study published in the journal Advances in Space Research proposed a low-cost space probe be sent to study Atira asteroids, citing the difficulty in observing the group from Earth as a reason to undertake the mission.[14] The study proposed that the mission would be powered by spacecraft electric propulsion and would follow a path designed to flyby as many Atira asteroids as possible. The probe would also attempt to discover new NEOs that may pose a threat to Earth.[14]

Related asteroid groups

ꞌAylóꞌchaxnim asteroids

ꞌAylóꞌchaxnim asteroids, which had been provisionally nicknamed "Vatira" asteroids before the first was discovered,Template:Efn are a subclass of Atiras that orbit entirely interior to the orbit of Venus, aka 0.718 AU.[15] Despite their orbits placing them at a significant distance from Earth, they are still classified as near-Earth objects.[16] Observations suggest that ꞌAylóꞌchaxnim asteroids frequently have their orbits altered into Atira asteroids and vice versa.[17]

First formally theorised to exist by William F. Bottke and Gianluca Masi in 2002 and 2003,[18][19] the first and to date only such asteroid found is 594913 ꞌAylóꞌchaxnim,[20][21] which was discovered on 4 January 2020 by the Zwicky Transient Facility. As the archetype, it subsequently gave its name to the class.[15] It has an aphelion of only 0.656 AU, the smallest of any known asteroid.[9][12]

Vulcanoids

Script error: No such module "Labelled list hatnote". No asteroids have yet been discovered to orbit entirely inside the orbit of Mercury (q = 0.307 AU). Such hypothetical asteroids would likely be termed vulcanoids, although the term often refers to asteroids which more specifically have remained in the intra-Mercurian region over the age of the Solar System.[22]

Members

The following table lists the known and suspected Atiras since November 2025Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters".. 594913 ꞌAylóꞌchaxnim, due to its unique classification, has been highlighted in pink. The interior planets Mercury and Venus have been included for comparison as grey rows.

List of known and suspected Atiras as of October 2025 (Q < 0.983 AU)[9]
Designation Perihelion
(AU) 		Semi-major axis
(AU) 		Aphelion
(AU) 		Eccentricity Inclination
(°) 		Period
(days) 		Observation arc
(days) 		(H) Diameter(A)
(m) 		Discoverer Ref
Mercury
(for comparison)Script error: No such module "Check for unknown parameters".		 0.307 0.3871 0.467 0.2056 7.01 88 NA −0.6 Script error: No such module "sort". NA
Venus
(for comparison)Script error: No such module "Check for unknown parameters".		 0.718 0.7233 0.728 0.0068 3.39 225 NA −4.5 Script error: No such module "sort". NA
Template:Mpl 0.404 0.6923 0.980 0.4160 2.02 210 1 25.0 Script error: No such module "sort". David J. Tholen Template:M+J
163693 Atira 0.502 0.7410 0.980 0.3221 25.62 233 7766 16.4 Script error: No such module "sort". LINEAR Template:LoMP
Template:M+J
Template:Mp 0.337 0.6176 0.898 0.4545 2.95 177 3564 20.5 Script error: No such module "sort". David J. Tholen Template:LoMP
Template:M+J
Template:Mpl 0.298 0.6352 0.973 0.5311 18.94 185 6227 18.5 Script error: No such module "sort". LONEOS Template:LoMP
Template:M+J
Template:Mp 0.428 0.6813 0.935 0.3723 23.33 205 7031 17.6 Script error: No such module "sort". Catalina Sky Survey Template:LoMP
Template:M+J
Template:Mpl
(aka Template:Mpl)Script error: No such module "Check for unknown parameters".		 0.262 0.6008 0.940 0.5641 10.76 170 5110 20.1 Script error: No such module "sort". Mount Lemmon Survey
Pan-STARRS		 Template:M+J
Template:Mp 0.641 0.7848 0.928 0.1829 24.77 254 4995 18.9 Script error: No such module "sort". Mount Lemmon Survey Template:LoMP
Template:M+J
Template:Mp 0.428 0.6159 0.804 0.3050 28.26 177 5816 16.5 Script error: No such module "sort". Catalina Sky Survey Template:LoMP
Template:M+J
Template:Mp 0.431 0.6950 0.959 0.3799 24.31 212 5537 18.6 Script error: No such module "sort". Mount Lemmon Survey Template:LoMP
Template:M+J
Template:Mp 0.288 0.6181 0.948 0.5338 29.88 178 5183 19.7 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mp 0.455 0.7131 0.971 0.3612 6.67 220 2225 20.2 Script error: No such module "sort". Pan-STARRS Template:M+J
Template:Mp 0.262 0.6008 0.940 0.5642 10.77 170 5110 20.1 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mp 0.653 0.7737 0.894 0.1557 16.40 249 4031 19.9 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mp 0.548 0.7522 0.956 0.2711 19.20 238 3259 20.2 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mpl 0.352 0.6666 0.981 0.4715 4.06 199 2602 20.5 Script error: No such module "sort". Pan-STARRS Template:M+J
Template:Mp 0.646 0.8094 0.973 0.2016 17.18 266 1084 21.3 Script error: No such module "sort". Pan-STARRS Template:M+J
Template:Mp
(aka Template:Mp)Script error: No such module "Check for unknown parameters".		 0.329 0.6346 0.941 0.4823 19.85 185 2980 18.1 Script error: No such module "sort". Spacewatch
ATLAS		 Template:M+J
Template:Mp 0.485 0.6832 0.882 0.2904 40.39 206 3321 17.7 Script error: No such module "sort". Catalina Sky Survey Template:M+J
Template:Mpl 0.404 0.5886 0.774 0.3143 47.22 165 2996 17.5 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mpl 0.317 0.5554 0.794 0.4293 29.50 151 1108 17.3 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
594913 ꞌAylóꞌchaxnim 0.457 0.5553 0.654 0.1772 15.87 151 1827 16.2 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mpl 0.692 0.8197 0.947 0.1553 49.65 271 4043 19.0 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mpl 0.476 0.6376 0.800 0.2541 32.58 186 1179 18.7 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mp 0.396 0.5984 0.800 0.3376 31.73 169 1564 18.6 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mp 0.418 0.6764 0.935 0.3820 9.82 203 2860 20.1 Script error: No such module "sort". Scott S. Sheppard Template:M+J
Template:Mp 0.610 0.7174 0.825 0.1500 24.83 222 4448 18.8 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mpl 0.133 0.4618 0.790 0.7115 31.94 115 2552 17.7 Script error: No such module "sort". Scott S. Sheppard Template:M+J
Template:Mp 0.313 0.5339 0.755 0.4139 18.07 143 1716 18.0 Script error: No such module "sort". Zwicky Transient Facility Template:M+J
Template:Mp 0.590 0.7853 0.981 0.2487 15.83 254 816 19.4 Script error: No such module "sort". Kitt Peak-Bok Template:M+J
2023 EL 0.581 0.7714 0.961 0.2462 13.88 247 2864 19.2 Script error: No such module "sort". Scott S. Sheppard Template:M+J
Template:Mp 0.398 0.6036 0.809 0.3398 35.47 171 325 19.8 Script error: No such module "sort". Kitt Peak-Bok Template:M+J
Template:Mp 0.805 0.8722 0.939 0.0771 67.43 298 3318 18.8 Script error: No such module "sort". Pan-STARRS Template:M+J
Template:Mp 0.398 0.6033 0.809 0.3978 35.55 171 6 19.9 Script error: No such module "sort". Kitt Peak-Bok Template:M+J
Template:Mpl 0.322 0.6442 0.966 0.4998 24.47 189 3606 20.5 Script error: No such module "sort". Moonbase South Observatory Template:M+J
Template:Mp 0.803 0.8609 0.919 0.0672 21.17 292 1753 20.6 Script error: No such module "sort". Mount Lemmon Survey Template:M+J
Template:Mp 0.572 0.6795 0.787 0.1579 3.79 205 32 21.3 Script error: No such module "sort". Subaru Telescope, Maunakea Template:M+J
Template:Mpl 0.136 0.4620 0.788 0.7051 32.84 115 88 20.1 Script error: No such module "sort". Cerro Tololo-DECam Template:M+J
Template:Mp 0.623 0.7437 0.864 0.1624 33.34 234 110 19.6 Script error: No such module "sort". Cerro Tololo-DECam Template:M+J
Template:Mpl 0.273 0.4958 0.719 0.4499 16.77 128 10 18.8 Script error: No such module "sort". Cerro Tololo-DECam Template:M+J
(A) All diameter estimates are based on an assumed albedo of 0.14 (except 163693 Atira, for which the size has been directly measured; and 594913 ꞌAylóꞌchaxnim, for which an albedo of 0.22 is assumed based on its known stony composition)
(B) Binary asteroid

See also

Notes

Template:Notelist

References

  1. ↑ a b Script error: No such module "citation/CS1".
  2. ↑ a b Script error: No such module "citation/CS1".
  3. ↑ Script error: No such module "Citation/CS1".
  4. ↑ (Ulukau Hawaiian Electronic Library)
  5. ↑ Script error: No such module "Citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ a b c d Script error: No such module "Citation/CS1".
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ a b c Script error: No such module "citation/CS1".
  10. ↑ Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ a b Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ a b Script error: No such module "Citation/CS1".
  15. ↑ a b Script error: No such module "Citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "Citation/CS1".
  22. ↑ Script error: No such module "Citation/CS1".

External links

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