Atira asteroids /??t?r?/ 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
editNaming
editThere 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 [??po] 'circle' and hele [?h?l?] '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
editTheir 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[update], 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
editMost 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
editAtiras 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
editA 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]
Related asteroid groups
edit?Ayló?chaxnim asteroids
edit?Ayló?chaxnim 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 ?Ayló?chaxnim 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 ?Ayló?chaxnim,[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
editNo 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
editThe following table lists the known and suspected Atiras as of November 2024[update]. 594913 ?Ayló?chaxnim, due to its unique classification, has been highlighted in pink. The interior planets Mercury and Venus have been included for comparison as grey rows.
| 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 | 0.3222 | 25.62 | 233 | 6601 | 16.3 | 4800±500(B) | LINEAR | List MPC · JPL |
| (164294) 2004 XZ130 | 0.337 | 0.6176 | 0.898 | 0.4546 | 2.95 | 177 | 3564 | 20.4 | 300 | David J. Tholen | List MPC · JPL |
| (434326) 2004 JG6 | 0.298 | 0.6353 | 0.973 | 0.5311 | 18.94 | 185 | 6227 | 18.5 | 710 | LONEOS | List MPC · JPL |
| (413563) 2005 TG45 | 0.428 | 0.6814 | 0.935 | 0.3722 | 23.33 | 205 | 5814 | 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 | 4794 | 16.5 | 1,800 | Catalina Sky Survey | List MPC · JPL |
| (481817) 2008 UL90 | 0.431 | 0.6951 | 0.959 | 0.3798 | 24.31 | 212 | 4496 | 18.6 | 680 | Mount Lemmon Survey | List MPC · JPL |
| 2010 XB11 | 0.288 | 0.6180 | 0.948 | 0.5339 | 29.89 | 177 | 1811 | 19.9 | 370 | Mount Lemmon Survey | MPC · JPL |
| 2012 VE46 | 0.455 | 0.7131 | 0.971 | 0.3613 | 6.67 | 220 | 2225 | 20.2 | 320 | Pan-STARRS | MPC · JPL |
| 2013 TQ5 | 0.653 | 0.7737 | 0.894 | 0.1557 | 16.40 | 249 | 2269 | 19.8 | 390 | Mount Lemmon Survey | MPC · JPL |
| 2014 FO47 | 0.548 | 0.7522 | 0.956 | 0.2712 | 19.20 | 238 | 2779 | 20.3 | 310 | Mount Lemmon Survey | MPC · JPL |
| 2015 DR215 | 0.352 | 0.6665 | 0.981 | 0.4716 | 4.08 | 199 | 2156 | 20.4 | 300 | Pan-STARRS | MPC · JPL |
| 2017 XA1 | 0.646 | 0.8095 | 0.973 | 0.2017 | 17.18 | 266 | 1084 | 21.3 | 200 | Pan-STARRS | MPC · JPL |
| (678861) 2017 YH (aka 2016 XJ24) |
0.328 | 0.6343 | 0.940 | 0.4825 | 19.85 | 185 | 1127 | 18.4 | 740 | Spacewatch ATLAS |
MPC · JPL |
| 2018 JB3 | 0.485 | 0.6832 | 0.882 | 0.2904 | 40.39 | 206 | 2037 | 17.7 | 1,020 | Catalina Sky Survey | MPC · JPL |
| 2019 AQ3 | 0.404 | 0.5887 | 0.774 | 0.3143 | 47.22 | 165 | 2175 | 17.5 | 1,120 | Zwicky Transient Facility | MPC · JPL |
| 2019 LF6 | 0.317 | 0.5554 | 0.794 | 0.4293 | 29.51 | 151 | 796 | 17.3 | 1,230 | Zwicky Transient Facility | MPC · JPL |
| 594913 ?Ayló?chaxnim | 0.457 | 0.5554 | 0.654 | 0.1770 | 15.87 | 151 | 609 | 16.2 | 1500+1100 ?600 |
Zwicky Transient Facility | MPC · JPL |
| 2020 HA10 | 0.692 | 0.8196 | 0.947 | 0.1552 | 49.65 | 271 | 3248 | 18.9 | 590 | Mount Lemmon Survey | MPC · JPL |
| 2020 OV1 | 0.476 | 0.6376 | 0.800 | 0.2541 | 32.58 | 186 | 1169 | 18.9 | 590 | Zwicky Transient Facility | MPC · JPL |
| 2021 BS1 | 0.396 | 0.5984 | 0.800 | 0.3377 | 31.73 | 169 | 46 | 18.5 | 710 | Zwicky Transient Facility | MPC · JPL |
| 2021 LJ4 | 0.416 | 0.6748 | 0.933 | 0.3834 | 9.83 | 202 | 5 | 20.1 | 340 | Scott S. Sheppard | MPC · JPL |
| 2021 PB2 | 0.610 | 0.7174 | 0.825 | 0.1501 | 24.83 | 222 | 3392 | 18.8 | 620 | Zwicky Transient Facility | MPC · JPL |
| 2021 PH27 | 0.133 | 0.4617 | 0.790 | 0.7117 | 31.93 | 115 | 1515 | 17.7 | 1,020 | Scott S. Sheppard | MPC · JPL |
| 2021 VR3 | 0.313 | 0.5339 | 0.755 | 0.4138 | 18.06 | 143 | 1012 | 18.0 | 890 | Zwicky Transient Facility | MPC · JPL |
| 2022 BJ8 | 0.590 | 0.7852 | 0.981 | 0.2487 | 15.83 | 254 | 102 | 19.6 | 430 | Kitt Peak-Bok | MPC · JPL |
| 2023 EL | 0.579 | 0.7676 | 0.956 | 0.2453 | 13.63 | 246 | 9 | 18.9 | 580 | Scott S. Sheppard | 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 | 0.321 | 0.6436 | 0.966 | 0.5010 | 24.63 | 189 | 3 | 20.5 | 280 | Moonbase South Observatory | MPC · JPL |
| 2024 UM9 | 0.803 | 0.8608 | 0.919 | 0.0675 | 21.14 | 291 | 5 | 20.8 | 250 | Mount Lemmon Survey | 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)
- (B) Binary asteroid
See also
editNotes
edit- ^ 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 "Ali?i", 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 - ^ Namely, they have coupled oscillations in orbital eccentricity and inclination
- ^ The nickname "Vatira" combined "Venus" with "Atira".[15]
References
edit- ^ a b Baalke, Ron. "Near-Earth Object Groups". Jet Propulsion Laboratory. NASA. Archived from the original on 2 February 2002. Retrieved 11 November 2016.
- ^ a b Chodas, Paul; Khudikyan, Shakeh; Chamberlin, Alan (14 May 2019). "Near-Earth Asteroid Discovery Statistics". Jet Propulsion Laboratory. NASA. Retrieved 25 May 2019.
- ^ 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.
- ^ (Ulukau Hawaiian Electronic Library)
- ^ 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.
- ^ 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.
- ^ 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.
- ^ "Minor Planet Circular 61768" (PDF). Minor Planet Center. Retrieved 2025-08-06.
- ^ a b c "JPL Small-Body Database Search Engine: Q < 0.983 (AU)". JPL Solar System Dynamics. NASA. Retrieved 30 December 2017.
- ^ "Small-Body Database Query". Solar System Dynamics – Jet Propulsion Laboratory. NASA – California Institute of Technology. Retrieved 2025-08-06.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ "JPL Small-Body Database Browser: 2020 AV2". Jet Propulsion Laboratory. NASA. Archived from the original on 11 January 2020. Retrieved 9 January 2020.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
External links
edit- List Of Aten Minor Planets, Minor Planet Center