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]

The first suspected Apohele was 1998 DK36, and the first confirmed was 163693 Atira in 2003. There are 18 suspected Apoheles,[2] of which 15 have well-known orbits, of which six have been determined with sufficient precision to receive a permanent number (see § List below).[3] An additional 58 objects (not listed) have aphelia smaller than Earth's aphelion (1.017 AU).[4] The Near Earth Object Surveillance Satellite is intended to find more.

In great part because of the search methods used to look for asteroids, there are currently no known asteroids with orbits contained within Venus or Mercury's (e.g. vulcanoids).

There is no standard name for the class. The name Apohele was proposed by the discoverers of 1998 DK36,[5] and is the Hawaiian word for orbit; 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).[6] Still others, following the general practice to name a new class of asteroids for the first recognized member of that class,[7][8] use the designation Atira asteroids.[1]

Apoheles do not cross Earth's orbit and are not immediate impact 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 orbits of many of these objects are strongly affected by the Kozai-Lidov mechanism, which contributes to enhanced long-term stability.[9]

List[edit]

List of known and suspected Apoheles as of May 2018 (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
163693 Atira 0.502 0.7411 0.980 0.3221 25.62 233 5192 16.3 4,800+1,000(B) LINEAR List
(164294) 2004 XZ130 0.337 0.6176 0.898 0.4546 2.95 177 3564 20.4 300 David J. Tholen List
(434326) 2004 JG6 0.298 0.6352 0.973 0.5312 18.94 185 4035 18.4 740 LONEOS List
(413563) 2005 TG45 0.428 0.6814 0.935 0.3722 23.33 205 4295 17.6 1,100 Catalina Sky Survey List
2013 JX28 (=2006 KZ39) 0.262 0.6008 0.940 0.5642 10.76 170 2893 20.1 340 Mount Lemmon Survey
Pan-STARRS
MPC
2006 WE4 0.641 0.7847 0.928 0.1829 24.77 254 4081 18.9 590 Mount Lemmon Survey MPC
(418265) 2008 EA32 0.428 0.6159 0.804 0.3050 28.26 177 3126 16.5 1,800 Catalina Sky Survey List
(481817) 2008 UL90 0.431 0.6950 0.959 0.3798 24.31 212 3441 18.7 650 Mount Lemmon Survey List
2010 XB11 0.288 0.618 0.948 0.5339 29.88 177 1811 19.9 450 Mount Lemmon Survey MPC
2012 VE46 0.455 0.7129 0.971 0.3615 6.67 220 1135 20.2 320 Pan-STARRS MPC
2013 TQ5 0.653 0.7737 0.894 0.1556 16.40 249 805 19.8 390 Mount Lemmon Survey MPC
2014 FO47 0.548 0.7521 0.956 0.2711 19.20 238 1407 20.3 310 Mount Lemmon Survey MPC
2015 DR215 0.352 0.6664 0.981 0.4716 4.09 199 404 20.3 310 Pan-STARRS MPC
2015 ME131 0.645 0.8049 0.971 0.1989 28.88 264 2 19.5 450 Pan-STARRS MPC
2017 XA1 0.646 0.8096 0.973 0.2016 17.18 266 41 21.2 200 Pan-STARRS MPC
2017 YH 0.328 0.6345 0.941 0.4824 19.83 185 391 18.5 710 Spacewatch MPC
2018 JB3 0.485 0.6832 0.882 0.2905 40.40 206 12 17.5 1,120 Catalina Sky Survey MPC
(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

Pseudo-Atiras[edit]

Two further asteroids technically pass further from the Sun than Earth does at its closest, but due to the eccentricity of Earth's orbit, still remain entirely within it. The known pseudo-Atira asteroids are listed below:

List of pseudo-Atiras as of May 2018 (Q < 1.017 AU)
Designation Perihelion
(AU)
Semi-major axis
(AU)
Aphelion
(AU)
Eccentricity Inclination
(°)
Period
(days)
Observation arc
(days)
(H) Diameter(A)
(m)
Discoverer Ref
2009 SZ99 0.481 0.8148 0.989 0.2144 21.33 269 2133 19.5 450 Mount Lemmon Survey MPC
2017 TF2 0.447 0.7154 0.984 0.3751 13.86 221 13 20.4 300 Mount Lemmon Survey MPC

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 December 2017. Retrieved 30 December 2017. 
  3. ^ a b "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 30 December 2017. 
  5. ^ 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. Retrieved 11 November 2016. 
  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. 143 (2): 421–424. Bibcode:2000Icar..143..421M. doi:10.1006/icar.1999.6282. Retrieved 11 November 2016. 
  7. ^ Wm. Robert Johnston (24 August 2006). "Names of Solar System objects and features". www.johnstonsarchive.net. Retrieved 11 November 2016. 
  8. ^ 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. Retrieved 11 November 2016. 
  9. ^ 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:1806.00442Freely accessible. Bibcode:2018RNAAS...2b..46D. doi:10.3847/2515-5172/aac9ce. 

External links[edit]