Atira asteroid

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 , after the Hawaiian word for orbit, from apo 'circle' and hele 'to go'. This was suggested partly because of its similarity to the words aphelion (apoapsis) and helios. Other authors adopted the designation "Inner Earth Objects" (IEOs). 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.

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. This means that Atiras can usually only be seen during twilight. 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.

The first confirmed Atira asteroid was 163693 Atira in 2003, discovered by the Lincoln Laboratory Near Earth Asteroid Research Team. , there are 34 known Atiras, two of which are named, nine of which have received a numbered designation, and seven of which are potentially hazardous objects.

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. A number of known Atiras could be fragments or former moons of larger Atiras as they exhibit an unusually high level of orbital correlation.{{Cite journal |doi-access = free

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, which contributes to enhanced long-term orbital stability, since there is no libration of the perihelion.

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. 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 NEOs that may pose a threat to Earth.

Related asteroid groups

ꞌAylóꞌchaxnim asteroids

ꞌAylóꞌchaxnim asteroids, which had been provisionally nicknamed "Vatira" asteroids before the first was discovered,{{efn|The nickname "Vatira" combined "Venus" with "Atira". Observations suggest that ꞌAylóꞌchaxnim asteroids frequently have their orbits altered into Atira asteroids and vice versa.

First formally theorised to exist by William F. Bottke and Gianluca Masi in 2002 and 2003,{{cite journal |last1=Bottke |first1=William F. |display-authors=et al|date=April 2002 |title=Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects

Vulcanoids

Main article: Vulcanoid

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.

Members

The following table lists the known and suspected Atiras . 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.

:(A) All diameter estimates are based on an assumed albedo of 0.14 (except 163693 Atira, for which the size has been directly measured; and 594913 ꞌAylóꞌchaxnim, for which an albedo of 0.22 is assumed based on its known stony composition) :(B) Binary asteroid

Notes

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}}

References

|author-link1 = David J. Tholen

|author-link1 = Patrick Michel |author-link2 = Vincenzo Zappalà

|display-authors = et al |access-date = 8 July 2020 |doi-access = free

References

1. [https://wehewehe.org/gsdl2.85/cgi-bin/hdict?a=d&d=D1434&l=en (Ulukau Hawaiian Electronic Library)]
2. (1 June 2016). "Dynamical study of the Atira group of asteroids". [[Monthly Notices of the Royal Astronomical Society]].
3. "Minor Planet Circular 61768". Minor Planet Center.
4. "Small-Body Database Query". NASA – California Institute of Technology.
5. (2020). "A Twilight Search for Atiras, Vatiras, and Co-orbital Asteroids: Preliminary Results". [[IOP Publishing]].
6. (11 June 2018). "Kozai--Lidov Resonant Behavior Among Atira-class Asteroids". [[Research Notes of the AAS]].
7. (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]].
8. (1 April 2017). "Optimised low-thrust mission to the Atira asteroids". [[Elsevier]].
9. "JPL Small-Body Database Browser: 2020 AV2". [[NASA]].
10. (4 December 2022). "The orbital evolution of Atira asteroids". [[Monthly Notices of the Royal Astronomical Society]].
11. Masi, Gianluca. (9 January 2020). "2020 AV2, the first intervenusian asteroid ever discovered: an image – 08 Jan. 2020". Virtual Telescope Project.
12. (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.
13. "Near-Earth Asteroid Discovery Statistics". link. (14 May 2019). [[NASA]]
14. "Near-Earth Object Groups". [[NASA]]. link