Atira asteroid

Atira asteroids 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 smallest group of near-Earth objects, compared to the 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)

Asteroids

The first suspected Apohele was 1998 DK36, and the first confirmed was 163693 Atira in 2003. As of August 2020, there are 23 known Apoheles,[2] of which 18 have robust orbit determinations, of which six have been computed with sufficient precision to receive a permanent number (see § List below).[3] An additional 92 objects (not listed) have aphelia smaller than Earth's aphelion (Q = 1.017 AU).[4] The Near Earth Object Surveillance Satellite is intended to find more.

On 4 January 2020, the Zwicky Transient Facility discovered 2020 AV2, whose aphelion distance is only 0.656 AU, which is entirely within the orbit of Venus, which never gets less than 0.718 AU from the Sun.[5][6] However, no asteroids have yet been discovered inside the orbit of Mercury (Q = 0.467 AU, e.g. vulcanoids). As of January 2020, the asteroid with the smallest known aphelion is 2020 AV₂, with an aphelion of 0.656 AU,[3][7] followed by 2019 AQ3 with Q = 0.774 AU and 2019 LF6 with Q = 0.794 AU.[8]

Apoheles 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. Although the dynamics of many of these objects somehow resembles the one induced by the Kozai-Lidov mechanism (coupled oscillations in eccentricity and inclination), which contributes to enhanced long-term stability, there is no libration of the value of the argument of perihelion.[7][9]

Vatira asteroids are a subclass of Atiras that orbit entirely interior to the orbit of Venus. They were theorized to exist at least since 2012,[10] and in early 2020, the first Vatira asteroid was discovered: 2020 AV2.[11][12][13]

Name

There is no standard name for the class. The name Apohele was proposed by the discoverers of 1998 DK36,[14] and is the Hawaiian word for orbit, from apo [ˈɐpo] 'circle' and hele [ˈhɛlɛ] 'to go';[15] it was chosen partially because of its similarity to the words aphelion (apoapsis) and helios.[lower-alpha 1] Other authors adopted the designation Inner Earth Objects (IEOs).[16] Still others, following the general practice to name a new class of asteroids for the first recognized member of that class,[17][18] use the designation Atira asteroids.[1]

'Vatira' is a conflation of 'Atira' with the 'v' of 'Venus'.

Members

List of known and suspected Apoheles as of August 2020 (Q < 0.983 AU)[3]

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	0.7411	0.980	0.3221	25.62	233	5192	16.3	4,800+1,000^(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	0.6352	0.973	0.5312	18.94	185	4035	18.4	740	LONEOS	List MPC · JPL
(413563) 2005 TG45	0.428	0.6814	0.935	0.3722	23.34	205	4744	17.6	1,100	Catalina Sky Survey	List MPC · JPL
2013 JX28 (aka 2006 KZ39)	0.262	0.6008	0.940	0.5642	10.76	170	2893	20.1	340	Mount Lemmon Survey Pan-STARRS	MPC · JPL
2006 WE4	0.641	0.7847	0.928	0.1829	24.77	254	4081	18.9	590	Mount Lemmon Survey	MPC · JPL
(418265) 2008 EA32	0.428	0.6159	0.804	0.3050	28.26	177	3126	16.5	1,800	Catalina Sky Survey	List MPC · JPL
(481817) 2008 UL90	0.431	0.6950	0.959	0.3798	24.31	212	3441	18.7	650	Mount Lemmon Survey	List MPC · JPL
2010 XB11	0.288	0.618	0.948	0.5339	29.88	177	1811	19.9	450	Mount Lemmon Survey	MPC · JPL
2012 VE46	0.455	0.7129	0.971	0.3615	6.67	220	1135	20.2	320	Pan-STARRS	MPC · JPL
2013 TQ5	0.653	0.7737	0.894	0.1556	16.40	249	805	19.8	390	Mount Lemmon Survey	MPC · JPL
2014 FO47	0.548	0.7521	0.956	0.2711	19.20	238	1407	20.3	310	Mount Lemmon Survey	MPC · JPL
2015 DR215	0.352	0.6664	0.981	0.4716	4.09	199	404	20.3	310	Pan-STARRS	MPC · JPL
2015 ME131	0.645	0.8049	0.971	0.1989	28.88	264	2	19.5	450	Pan-STARRS	MPC · JPL
2017 XA1	0.646	0.8096	0.973	0.2016	17.18	266	41	21.2	200	Pan-STARRS	MPC · JPL
2017 YH (aka 2016 XJ24)	0.328	0.6344	0.941	0.4825	19.83	185	757	18.5	710	Spacewatch ATLAS	MPC · JPL
2018 JB3	0.485	0.6832	0.882	0.2905	40.39	206	36	17.6	1,070	Catalina Sky Survey	MPC · JPL
2019 AQ3	0.404	0.5887	0.774	0.3143	47.22	165	1199	17.4	1,200	Zwicky Transient Facility	MPC · JPL
2019 LF6	0.317	0.5554	0.794	0.4293	29.51	151	358	17.2	1,300	Zwicky Transient Facility	MPC · JPL
2020 AV2	0.458	0.5557	0.654	0.1766	15.86	151	19	16.4	2,000	Zwicky Transient Facility	MPC · JPL
2020 HA10	0.694	0.8204	0.947	0.1544	49.66	271	5	19.1	540	Mount Lemmon Survey	MPC · JPL
2020 OV1	0.475	0.6375	0.800	0.2543	32.58	186	18	18.7	650	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

• List of minor planet groups
• List of minor planets

References

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 "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

1. "Near-Earth Object Groups". JPL – NASA. Retrieved 11 November 2016.
2. "Near-Earth Asteroid Discovery Statistics". 14 May 2019. Retrieved 25 May 2019.
3. "JPL Small-Body Database Search Engine: Q < 0.983 (AU)". JPL Solar System Dynamics. Retrieved 30 December 2017.
4. "Asteroids with aphelia between 0.983 and 1.017 AU". Retrieved 25 May 2019.
5. Greenstreet, Sarah (6 February 2020). "Orbital Dynamics of 2020 AV2: the First Vatira Asteroid". Monthly Notices of the Royal Astronomical Society: Letters. 493: L129–L131. arXiv:2001.09083. Bibcode:2020MNRAS.tmpL..23G. doi:10.1093/mnrasl/slaa025.
6. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (11 February 2020). "On the orbital evolution of 2020 AV2, the first asteroid ever observed to go around the Sun inside the orbit of Venus". Monthly Notices of the Royal Astronomical Society: Letters. 494 (1): L6. arXiv:2002.03033. Bibcode:2020MNRAS.494L...6D. doi:10.1093/mnrasl/slaa027.
7. 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...2b..46D. doi:10.3847/2515-5172/aac9ce.
8. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (25 July 2019). "Hot and Eccentric: The Discovery of 2019 LF₆ as a New Step in the Quest for the Vatira Population". Research Notes of the American Astronomical Society. 3 (7): 106. Bibcode:2019RNAAS...3g.106D. doi:10.3847/2515-5172/ab346c.
9. 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.
10. Greenstreet, Sarah; Ngo, Henry; Gladman, Brett (January 2012). "The orbital distribution of Near-Earth Objects inside Earth's orbit" (PDF). Icarus. 217 (1): 355–366. Bibcode:2012Icar..217..355G. doi:10.1016/j.icarus.2011.11.010. 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.
11. 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.
12. Plait, Phil (10 January 2020). "Meet 2020 AV2, the first asteroid found that stays inside Venus's orbit!". Bad Astronomy. Syfy Wire. Retrieved 10 January 2020.
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15. (Ulukau Hawaiian Electronic Library)
16. 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): 421–424. Bibcode:2000Icar..143..421M. doi:10.1006/icar.1999.6282.
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External links

• List Of Aten Minor Planets, Minor Planet Center