Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids whose orbits are entirely confined within Earth's orbit; 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.
The first suspected was 1998 DK36, and the first confirmed, was 163693 Atira in 2003. As of August 2021[update], there are 26 known Atiras, of which 19 have robust orbit determinations, of which six have been computed with sufficient precision to receive a permanent number. An additional 92 objects (not listed below) have aphelia smaller than Earth's aphelion (Q = 1.017 AU).
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. However, no asteroids have yet been discovered inside the orbit of Mercury (Q = 0.467 AU, e.g. vulcanoids). As of January 2020[update], the asteroid with the smallest known aphelion is 2020 AV2, with an aphelion of 0.656 AU, followed by 2019 AQ3 with Q = 0.774 AU and 2019 LF6 with Q = 0.794 AU.
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. Although the dynamics of many of these objects somehow resemble 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.
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, and in early 2020, the first Vatira asteroid was discovered: 2020 AV2.
There is no standard name for the class. Following the general practice to name a new class of asteroids for the first recognized member of that class, some astronomers, and this article, use the designation Atira asteroids.
The name Apohele was proposed by the discoverers of 1998 DK36, and is the Hawaiian word for orbit, from apo [ˈɐpo] 'circle' and hele [ˈhɛlɛ] 'to go'; 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). Still others,
'Vatira' is a conflation of 'Atira' with the 'v' of 'Venus'.
|1998 DK36||0.404||0.6923||0.980||0.4160||2.02||210||1||25.0||35||David J. Tholen||MPC · JPL|
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
(aka 2006 KZ39)
|0.262||0.6008||0.940||0.5642||10.76||170||2893||20.1||340||Mount Lemmon Survey
|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|
|2017 XA1||0.646||0.8096||0.973||0.2015||17.18||266||1084||21.2||200||Pan-STARRS||MPC · JPL|
(aka 2016 XJ24)
|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||560||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|
|2021 LJ4||0.416||0.6748||0.933||0.4161||9.83||202||5||20.0||360||Scott S. Sheppard||MPC · JPL|
|2021 PB2||0.606||0.7160||0.826||0.1535||25.14||221||4||18.7||640||Zwicky Transient Facility||MPC · JPL|
|2021 PH27||0.134||0.4614||0.789||0.7093||31.66||114||5||17.7||1,020||Scott S. Sheppard||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
- Cambridge Conference Correspondence, (2): WHAT'S IN A NAME: APOHELE = APOAPSIS & HELIOS – from Dave Tholen, Cambridge Conference Network (CCNet) DIGEST, 9 July 1998
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.
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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.
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- List Of Aten Minor Planets, Minor Planet Center