Wikipedia

Atira asteroid

Common orbital subgroups of Near-Earth Objects (NEOs)

Atira asteroids /əˈtɪrə/ 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

[edit]

Naming

[edit]

There is no official name for the class commonly referred as Atira asteroids. The term "Apohele asteroids" was proposed by the discoverers of 1998 DK36,[3] after the Hawaiian word for orbit, from apo [ˈɐpo] 'circle' and hele [ˈhɛlɛ] 'to go'.[4] This was suggested partly because of its similarity to the words aphelion (apoapsis) and helios.[a] 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

[edit]

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] As of January 2025, 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

[edit]

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

[edit]

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,[b] which contributes to enhanced long-term orbital stability, since there is no libration of the perihelion.[12][13]

Exploration

[edit]

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 NEO's that may pose a threat to Earth.[14]

[edit]

ꞌAylóꞌchaxnim asteroids

[edit]

ꞌAylóꞌchaxnim asteroids, which had been provisionally nicknamed "Vatira" asteroids before the first was discovered,[c] are a subclass of Atiras that orbit entirely interior to the orbit of Venus, aka 0.718 AU.[16] Despite their orbits placing them at a significant distance from Earth, they are still classified as near-Earth objects.[17] Observations suggest that ꞌAylóꞌchaxnim asteroids frequently have their orbits altered into Atira asteroids and vice versa.[18]

First formally theorised to exist by William F. Bottke and Gianluca Masi in 2002 and 2003,[19][20] the first and to date only such asteroid found is 594913 ꞌAylóꞌchaxnim,[21][22] which was discovered on 4 January 2020 by the Zwicky Transient Facility. As the archetype, it subsequently gave its name to the class.[16] It has an aphelion of only 0.656 AU, the smallest of any known asteroid.[9][12]

Vulcanoids

[edit]
Main article: Vulcanoid

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.[15]

Members

[edit]

The following table lists the known and suspected Atiras as of November 2024. 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)		 0.307 0.3871 0.467 0.2056 7.01 88 NA −0.6 4,879,400 NA
Venus
(for comparison)		 0.718 0.7233 0.728 0.0068 3.39 225 NA −4.5 12,103,600 NA
1998 DK36 0.404 0.6923 0.980 0.4160 2.02 210 1 25.0 35 David J. Tholen MPC · JPL
163693 Atira 0.502 0.7410 0.980 0.3221 25.62 233 7766 16.4 4800±500(B) LINEAR List
MPC · JPL
(164294) 2004 XZ130 0.337 0.6176 0.898 0.4545 2.95 177 3564 20.5 290 David J. Tholen List
MPC · JPL
(434326) 2004 JG6 0.298 0.6352 0.973 0.5311 18.94 185 6227 18.5 710 LONEOS List
MPC · JPL
(413563) 2005 TG45 0.428 0.6813 0.935 0.3723 23.33 205 7031 17.6 1,100 Catalina Sky Survey List
MPC · JPL
2013 JX28
(aka 2006 KZ39)		 0.262 0.6008 0.940 0.5641 10.76 170 5110 20.1 340 Mount Lemmon Survey
Pan-STARRS		 MPC · JPL
(613676) 2006 WE4 0.641 0.7848 0.928 0.1829 24.77 254 4995 18.9 590 Mount Lemmon Survey List
MPC · JPL
(418265) 2008 EA32 0.428 0.6159 0.804 0.3050 28.26 177 5816 16.5 1,800 Catalina Sky Survey List
MPC · JPL
(481817) 2008 UL90 0.431 0.6950 0.959 0.3799 24.31 212 5537 18.6 680 Mount Lemmon Survey List
MPC · JPL
2010 XB11 0.288 0.6181 0.948 0.5338 29.88 178 5183 19.7 410 Mount Lemmon Survey MPC · JPL
2012 VE46 0.455 0.7131 0.971 0.3612 6.67 220 2225 20.2 320 Pan-STARRS MPC · JPL
2013 JX28 0.262 0.6008 0.940 0.5642 10.77 170 5110 20.1 340 Mount Lemmon Survey MPC · JPL
2013 TQ5 0.653 0.7737 0.894 0.1557 16.40 249 4031 19.9 380 Mount Lemmon Survey MPC · JPL
2014 FO47 0.548 0.7522 0.956 0.2711 19.20 238 3259 20.2 320 Mount Lemmon Survey MPC · JPL
2015 DR215 0.352 0.6666 0.981 0.4715 4.06 199 2602 20.5 280 Pan-STARRS MPC · JPL
2017 XA1 0.646 0.8094 0.973 0.2016 17.18 266 1084 21.3 200 Pan-STARRS MPC · JPL
(678861) 2017 YH
(aka 2016 XJ24)		 0.329 0.6346 0.941 0.4823 19.85 185 2980 18.1 840 Spacewatch
ATLAS		 MPC · JPL
2018 JB3 0.485 0.6832 0.882 0.2904 40.39 206 3321 17.7 1,020 Catalina Sky Survey MPC · JPL
2019 AQ3 0.404 0.5886 0.774 0.3143 47.22 165 2996 17.5 1,120 Zwicky Transient Facility MPC · JPL
2019 LF6 0.317 0.5554 0.794 0.4293 29.50 151 1108 17.3 1,230 Zwicky Transient Facility MPC · JPL
594913 ꞌAylóꞌchaxnim 0.457 0.5553 0.654 0.1772 15.87 151 1827 16.2 1,700 Zwicky Transient Facility MPC · JPL
2020 HA10 0.692 0.8197 0.947 0.1553 49.65 271 4043 19.0 560 Mount Lemmon Survey MPC · JPL
2020 OV1 0.476 0.6376 0.800 0.2541 32.58 186 1179 18.7 640 Zwicky Transient Facility MPC · JPL
2021 BS1 0.396 0.5984 0.800 0.3376 31.73 169 1564 18.6 670 Zwicky Transient Facility MPC · JPL
2021 LJ4 0.418 0.6764 0.935 0.3820 9.82 203 2860 20.1 340 Scott S. Sheppard MPC · JPL
2021 PB2 0.610 0.7174 0.825 0.1500 24.83 222 4448 18.8 610 Zwicky Transient Facility MPC · JPL
2021 PH27 0.133 0.4618 0.790 0.7115 31.94 115 2552 17.7 1,020 Scott S. Sheppard MPC · JPL
2021 VR3 0.313 0.5339 0.755 0.4139 18.07 143 1716 18.0 890 Zwicky Transient Facility MPC · JPL
2022 BJ8 0.590 0.7853 0.981 0.2487 15.83 254 816 19.4 470 Kitt Peak-Bok MPC · JPL
2023 EL 0.581 0.7714 0.961 0.2462 13.88 247 2864 19.2 520 Scott S. Sheppard MPC · JPL
2023 EY2 0.398 0.6036 0.809 0.3398 35.47 171 325 19.8 400 Kitt Peak-Bok MPC · JPL
2023 KQ5 0.805 0.8722 0.939 0.0771 67.43 298 3318 18.8 630 Pan-STARRS MPC · JPL
2023 EY2 0.398 0.6033 0.809 0.3978 35.55 171 6 19.9 370 Kitt Peak-Bok MPC · JPL
2023 WK3 0.322 0.6442 0.966 0.4998 24.47 189 3606 20.5 290 Moonbase South Observatory MPC · JPL
2024 UM9 0.803 0.8609 0.919 0.0672 21.17 292 1753 20.6 260 Mount Lemmon Survey MPC · JPL
2024 WD19 0.572 0.6795 0.787 0.1579 3.79 205 32 21.3 190 Subaru Telescope, Maunakea MPC · JPL
2025 GN1 0.136 0.4620 0.788 0.7051 32.84 115 88 20.1 350 Cerro Tololo-DECam MPC · JPL
2025 LP 0.623 0.7437 0.864 0.1624 33.34 234 110 19.6 430 Cerro Tololo-DECam MPC · JPL
2025 SC79 0.273 0.4958 0.719 0.4499 16.77 128 10 18.8 620 Cerro Tololo-DECam MPC · JPL
(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

[edit]

Notes

[edit]
  1. ^ Cambridge Conference Correspondence, (2): WHAT'S IN A NAME: APOHELE = APOAPSIS & HELIOS – from Dave Tholen, Cambridge Conference Network (CCNet) DIGEST, 9 July 1998
    Benny,
    Duncan Steel has already brought up the subject of a class name for objects with orbits interior to the Earth's. To be sure, we've already given that subject some thought. I also wanted a word that begins with the letter "A", but there was some desire to work Hawaiian culture into it. I consulted with a friend of mine that has a master's degree in the Hawaiian language, and she recommended "Apohele", the Hawaiian word for "orbit". I found that an interesting suggestion, because of the similarity to fragments of "apoapsis" and "helios", and these objects would have their apoapsis closer to the Sun than the Earth's orbit. By the way, the pronunciation would be like "ah-poe-hey-lay". Rob Whiteley has suggested "Aliʻi", which refers to the Hawaiian elite, which provides a rich bank of names for discoveries in this class, such as Kuhio, Kalakaua, Kamehameha, Liliuokalani, and so on. Unfortunately, I think the okina (the reverse apostrophe) would be badly treated by most people.
    I wasn't planning to bring it up at this stage, but because Duncan has already done so, here's what we've got on the table so far. I'd appreciate some feedback on the suggestions.
    --Dave
  2. ^ Namely, they have coupled oscillations in orbital eccentricity and inclination
  3. ^ The nickname "Vatira" combined "Venus" with "Atira".[15]

References

[edit]
  1. ^ a b Baalke, Ron. "Near-Earth Object Groups". Jet Propulsion Laboratory. NASA. Archived from the original on 2 February 2002. Retrieved 11 November 2016.
  2. ^ a b Chodas, Paul; Khudikyan, Shakeh; Chamberlin, Alan (14 May 2019). "Near-Earth Asteroid Discovery Statistics". Jet Propulsion Laboratory. NASA. Retrieved 25 May 2019.
  3. ^ Tholen, David J.; Whiteley, Robert J. (September 1998). "Results From NEO Searches At Small Solar Elongation". American Astronomical Society. 30: 1041. Bibcode:1998DPS....30.1604T.
  4. ^ (Ulukau Hawaiian Electronic Library)
  5. ^ Michel, Patrick; Zappalà, Vincenzo; Cellino, Alberto; Tanga, Paolo (February 2000). "NOTE: Estimated Abundance of Atens and Asteroids Evolving on Orbits between Earth and Sun". Icarus. 143 (2). Harcourt: 421–424. Bibcode:2000Icar..143..421M. doi:10.1006/icar.1999.6282.
  6. ^ Ribeiro, Anderson O.; et al. (1 June 2016). "Dynamical study of the Atira group of asteroids". Monthly Notices of the Royal Astronomical Society. 458 (4): 4471–4476. doi:10.1093/mnras/stw642.
  7. ^ a b c d Ye, Quanzhi; et al. (2020). "A Twilight Search for Atiras, Vatiras, and Co-orbital Asteroids: Preliminary Results". The Astronomical Journal. 159 (2). IOP Publishing: 70. arXiv:1912.06109. Bibcode:2020AJ....159...70Y. doi:10.3847/1538-3881/ab629c. S2CID 209324310.
  8. ^ "Minor Planet Circular 61768" (PDF). Minor Planet Center. Retrieved 2024-08-22.
  9. ^ a b c "JPL Small-Body Database Search Engine: Q < 0.983 (AU)". JPL Solar System Dynamics. NASA. Retrieved 30 December 2017.
  10. ^ "Small-Body Database Query". Solar System Dynamics – Jet Propulsion Laboratory. NASA – California Institute of Technology. Retrieved 2025-01-17.
  11. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (20 December 2023). "Baked before Breaking into Bits: Evidence for Atira-type Asteroid Splits". Research Notes of the American Astronomical Society. 7 (12): 278 (3 pages). Bibcode:2023RNAAS...7..278D. doi:10.3847/2515-5172/ad16de.
  12. ^ a b de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (11 June 2018). "Kozai--Lidov Resonant Behavior Among Atira-class Asteroids". Research Notes of the AAS. 2 (2): 46. arXiv:1806.00442. Bibcode:2018RNAAS...2...46D. doi:10.3847/2515-5172/aac9ce. S2CID 119239031.
  13. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (1 August 2019). "Understanding the evolution of Atira-class asteroid 2019 AQ3, a major step towards the future discovery of the Vatira population". Monthly Notices of the Royal Astronomical Society. 487 (2): 2742–2752. arXiv:1905.08695. Bibcode:2019MNRAS.487.2742D. doi:10.1093/mnras/stz1437. S2CID 160009327.
  14. ^ a b Di Carlo, Marilena; Martin, Juan Manuel Romero; Gomez, Natalia Ortiz; Vasile, Massimiliano (1 April 2017). "Optimised low-thrust mission to the Atira asteroids". Advances in Space Research. 59 (7). Elsevier: 1724–1739. Bibcode:2017AdSpR..59.1724D. doi:10.1016/j.asr.2017.01.009. S2CID 116216149. Retrieved February 9, 2023.
  15. ^ a b Greenstreet, Sarah; Ngo, Henry; Gladman, Brett (January 2012). "The orbital distribution of Near-Earth Objects inside Earth's orbit" (PDF). Icarus. 217 (1). Elsevier: 355–366. Bibcode:2012Icar..217..355G. doi:10.1016/j.icarus.2011.11.010. hdl:2429/37251. We have provisionally named objects with 0.307 < Q < 0.718 AU Vatiras, because they are Atiras which are decoupled from Venus. Provisional because it will be abandoned once the first discovered member of this class will be named.
  16. ^ a b Bolin, Bryce T.; et al. (November 2022). "The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus" (PDF). Monthly Notices of the Royal Astronomical Society: Letters. 517 (1): L49 – L54. doi:10.1093/mnrasl/slac089. Retrieved 1 October 2022.
  17. ^ "JPL Small-Body Database Browser: 2020 AV2". Jet Propulsion Laboratory. NASA. Archived from the original on 11 January 2020. Retrieved 9 January 2020.
  18. ^ Lai, H.T.; Ip, W.H. (4 December 2022). "The orbital evolution of Atira asteroids". Monthly Notices of the Royal Astronomical Society. 517 (4): 5921–5929. arXiv:2210.09652. doi:10.1093/mnras/stac2991. Retrieved February 9, 2023.
  19. ^ Bottke, William F.; et al. (April 2002). "Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects". Icarus. 156 (2): 399–433. Bibcode:2002Icar..156..399B. doi:10.1006/icar.2001.6788.
  20. ^ Masi, Gianluca (June 2003). "Searching for inner-Earth objects: a possible ground-based approach". Icarus. 163 (2): 389–397. Bibcode:2003Icar..163..389M. doi:10.1016/S0019-1035(03)00082-4.
  21. ^ Masi, Gianluca (9 January 2020). "2020 AV2, the first intervenusian asteroid ever discovered: an image – 08 Jan. 2020". Virtual Telescope Project. Retrieved 9 January 2020.
  22. ^ Popescu, Marcel M.; et al. (11 August 2020). "Physical characterization of 2020 AV2, the first known asteroid orbiting inside Venus orbit". Monthly Notices of the Royal Astronomical Society. 496 (3): 3572–3581. arXiv:2006.08304. Bibcode:2020MNRAS.496.3572P. doi:10.1093/mnras/staa1728. S2CID 219687045. Retrieved 8 July 2020.
[edit]