Atira asteroid

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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)

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]

Asteroids[edit]

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[edit]

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.[a] 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[edit]

List of known and suspected Apoheles as of March 2021 (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 0.2015 17.18 266 1084 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 40.39 206 419 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 0.457 0.5554 0.654 0.1770 15.87 151 327 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 Zwicky Transient Facility MPC · JPL
2021 BS1 0.402 0.6015 0.801 0.3310 31.23 170 8 18.5 710 Zwicky Transient Facility 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[edit]

References[edit]

  1. ^ Cambridge Conference Correspondence, (2): WHAT'S IN A NAME: APOHELE = APOAPSIS & HELIOSfrom 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. ^ a b "Near-Earth Object Groups". JPL – NASA. Retrieved 11 November 2016.
  2. ^ a b "Near-Earth Asteroid Discovery Statistics". 14 May 2019. Retrieved 25 May 2019.
  3. ^ a b c "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 (1): L129–L131. arXiv:2001.09083. Bibcode:2020MNRAS.493L.129G. doi:10.1093/mnrasl/slaa025. S2CID 210911743.
  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. S2CID 211068996.
  7. ^ 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...2b..46D. doi:10.3847/2515-5172/aac9ce. S2CID 119239031.
  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. S2CID 160009327.
  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. 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.
  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.
  13. ^ Popescu, M.; de León, J.; de la Fuente Marcos, C.; Vaduvescu, O.; de la Fuente Marcos, R.; Licandro, J.; Pinter, V.; Zamora, O.; Fariña, C.; Curelaru, L. (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.
  14. ^ Tholen, D. J.; Whiteley, R. J. (September 1998). "Results From NEO Searches At Small Solar Elongation". American Astronomical Society. 30: 1041. Bibcode:1998DPS....30.1604T.
  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.
  17. ^ Wm. Robert Johnston (24 August 2006). "Names of Solar System objects and features". www.johnstonsarchive.net. Retrieved 11 November 2016.
  18. ^ Shoemaker, E. M. (December 1982). "Asteroid and comet bombardment of the earth". Annual Review of Earth and Planetary Sciences. 11: 461–494. Bibcode:1983AREPS..11..461S. doi:10.1146/annurev.ea.11.050183.002333.

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