Atira asteroid

Atira asteroids /əˈtɪrə/ or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids 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]

The group of Atira (Apohele) asteroids compared to the orbits of the terrestrial planets of the Solar System.

  Mars (M)
  Venus (V)
  Mercury (H)

  Sun
  Atira asteroids
  Earth (E)

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 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.[lower-alpha 1] 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 suspected Atira asteroid was 1998 DK₃₆, which was discovered by David J. Tholen of the Mauna Kea Observatory, but the first to be confirmed as such was 163693 Atira in 2003, discovered by the Arecibo Observatory. As of February 2023, there are 28 known Atiras, two of which are named, eight of which have received a numbered designation, and six of which are potentially hazardous objects.[2][8][9] An additional 127 objects have aphelia smaller than Earth's aphelion (Q = 1.017 AU).[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]

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,[lower-alpha 2] which contributes to enhanced long-term orbital stability, since there is no libration of the perihelion.[11][12]

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.[13] 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.[13]

Related asteroid groups

ꞌAylóꞌchaxnim asteroids

ꞌAylóꞌchaxnim asteroids, which had been provisionally nicknamed "Vatira" asteroids before the first was discovered,[lower-alpha 3] 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 Sarah Greenstreet, Henry Ngo, and Brett Gladman in 2012,[7] the first and to date only such asteroid found is 594913 ꞌAylóꞌchaxnim,[18][19] 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, making it the asteroid with the smallest known aphelion.[8][11]

Vulcanoids

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.[14]

Members

The following table lists the known and suspected Atiras as of June 2023. 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 February 2021 (Q < 0.983 AU)[8]
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
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 ꞌAylóꞌchaxnim	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

^(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

Notes

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
Namely, they have coupled oscillations in orbital eccentricity and inclination
The nickname "Vatira" combined "Venus" with "Atira".[14]

References

Baalke, Ron. "Near-Earth Object Groups". Jet Propulsion Laboratory. NASA. Archived from the original on 2 February 2002. Retrieved 11 November 2016.
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. Harcourt. 143 (2): 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.
Ye, Quanzhi; et al. (2020). "A Twilight Search for Atiras, Vatiras, and Co-orbital Asteroids: Preliminary Results". The Astronomical Journal. IOP Publishing. 159 (2): 70. arXiv:1912.06109. Bibcode:2020AJ....159...70Y. doi:10.3847/1538-3881/ab629c. S2CID 209324310.
"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 2023-02-05.
"Asteroids with aphelia between 0.983 and 1.017 AU". Retrieved 25 May 2019.
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.
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. Elsevier. 59 (7): 1724–1739. Bibcode:2017AdSpR..59.1724D. doi:10.1016/j.asr.2017.01.009. S2CID 116216149. Retrieved February 9, 2023.
Greenstreet, Sarah; Ngo, Henry; Gladman, Brett (January 2012). "The orbital distribution of Near-Earth Objects inside Earth's orbit" (PDF). Icarus. Elsevier. 217 (1): 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.
Bolin, Bryce T.; et al. (November 2022). "The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus". 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.
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

List Of Aten Minor Planets, Minor Planet Center

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[Tholen-CCC-5] 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

[12] Namely, they have coupled oscillations in orbital eccentricity and inclination

[17] The nickname "Vatira" combined "Venus" with "Atira".[14]

[NEO-groups-1] Baalke, Ron. "Near-Earth Object Groups". Jet Propulsion Laboratory. NASA. Archived from the original on 2 February 2002. Retrieved 11 November 2016.

[neo-jpl-stats-2] Chodas, Paul; Khudikyan, Shakeh; Chamberlin, Alan (14 May 2019). "Near-Earth Asteroid Discovery Statistics". Jet Propulsion Laboratory. NASA. Retrieved 25 May 2019.

[Tholen-1998-3] 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)

[Michel-2000-6] 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. Harcourt. 143 (2): 421–424. Bibcode:2000Icar..143..421M. doi:10.1006/icar.1999.6282.

[Ribeiro-7] 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.

[Sparkle-8] Ye, Quanzhi; et al. (2020). "A Twilight Search for Atiras, Vatiras, and Co-orbital Asteroids: Preliminary Results". The Astronomical Journal. IOP Publishing. 159 (2): 70. arXiv:1912.06109. Bibcode:2020AJ....159...70Y. doi:10.3847/1538-3881/ab629c. S2CID 209324310.

[jpl-search-by-smallest-aphelion-9] "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 2023-02-05.

[JPL_Horizons1-11] "Asteroids with aphelia between 0.983 and 1.017 AU". Retrieved 25 May 2019.

[FuenteMarcos20190611-13] 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.

[FuenteMarcos20190801-14] 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.

[Explore-15] 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. Elsevier. 59 (7): 1724–1739. Bibcode:2017AdSpR..59.1724D. doi:10.1016/j.asr.2017.01.009. S2CID 116216149. Retrieved February 9, 2023.

[Greenstreet2012-16] Greenstreet, Sarah; Ngo, Henry; Gladman, Brett (January 2012). "The orbital distribution of Near-Earth Objects inside Earth's orbit" (PDF). Icarus. Elsevier. 217 (1): 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.

[Bolin-18] Bolin, Bryce T.; et al. (November 2022). "The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus". Monthly Notices of the Royal Astronomical Society: Letters. 517 (1): L49–L54. doi:10.1093/mnrasl/slac089. Retrieved 1 October 2022.

[19] "JPL Small-Body Database Browser: 2020 AV2". Jet Propulsion Laboratory. NASA. Archived from the original on 11 January 2020. Retrieved 9 January 2020.

[20] 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.

[vt20200109-21] 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.

[Popescuetal2020-22] 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.