163693 Atira

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163693 Atira (Script error: No such module "IPAc-en".; provisional designation Template:Mp) is a stony asteroid, dwelling in the interior of Earth's orbit. It is classified as a near-Earth object. Atira is a binary asteroid, a system of two asteroids orbiting their common barycenter. The primary component with a diameter of approximately Script error: No such module "convert".[1] is orbited by a minor-planet moon that measures about Script error: No such module "convert"..[2] Atira was discovered on 11 February 2003, by astronomers with the Lincoln Near-Earth Asteroid Research at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.[3][4] To date, it is the only confirmed binary asteroid that orbits inside Earths orbit.[5]

It is the namesake and the first numbered body of the Atira asteroids, a new subclass of near-Earth asteroids, which have their orbits entirely within that of Earth and are therefore alternatively called Interior-Earth Objects (IEO).[6][7][8] As of 2019, there are only 36 known members of the Atira group of asteroids.[9] Atiras are similar to the larger group of Aten asteroids, as both are near-Earth objects and both have a semi-major axis smaller than that of Earth (< 1.0 AU). However, and contrary to Aten asteroids, the aphelion for Atiras is always smaller than Earth's perihelion (< 0.983 AU),[10] which means that they do not approach Earth as close as Atens do in general. Atira has an Earth minimum orbit intersection distance of Script error: No such module "convert". or approximately 80.1 lunar distances.[6]

Physical properties

Atira is a S-type asteroid and orbits the Sun at a distance of 0.5–1.0 AU once every 8 months (233 days). Its orbit has an eccentricity of 0.32 and an inclination of 26° with respect to the ecliptic.[6] With a perihelion of 0.50 AU the body also classifies as a Venus-crosserTemplate:Snd as Venus orbits the Sun at a distance of 0.72–0.73 AUTemplate:Snd but does not get as close to the Sun as Mercury (which orbits between 0.31 and 0.47 AU). As no precoveries were found, AtiraTemplate:'s observation arc begins with its discovery observation in 2003.[3] It has a rotation period of 3.3984 hours with a brightness variation of 0.36 magnitude (U=2Script error: No such module "Check for unknown parameters".) and a very low albedo of 0.0231.[1]

With a diameter of 4.8 kilometers, Atira is one of the largest Near-Earth objects. Early estimates of its size ranged from 1 to 2 kilometers,[4] but those were based on an assumed higher albedo of 0.20. Its larger size and low albedo were discovered when Atira was imaged by radar in early 2017.[2] These radar images also revealed that Atira is a binary asteroid.

Binary system

File:Atira.23jan17.u2.s1p0.gif
Arecibo follow-up observations from 23 January 2017

Atira came within Script error: No such module "convert". from Earth in January 2017, the closest since its discovery in 2003.[6] This provided an opportunity to study the asteroid by radar. Images taken at Arecibo Observatory on 20 January 2017 revealed that Atira is a synchronous binary asteroid with a minor-planet moon.[2][11] The primary with a diameter of Script error: No such module "val". is possibly elongated and very angular in shape. The secondary is tidally locked and has a diameter of Script error: No such module "val".. Additional images taken on 23 January 2017 showed that the two components are orbiting each other at a distance of about 6 km with an orbital period of 15.5 hours.[2][12] It is currently the only confirmed binary asteroid that orbits inside Earths orbit.[13]

Name

Because the first known object in a new class of asteroids will become the name of the new class, due consideration was given to the name for (163693). The other classes of near-Earth asteroids, Amors, Apollos, and Atens, are named after a Roman, Greek, and Egyptian god respectively, each of which begins with the letter 'A'. Atira follows this pattern, being named after [[Atira (goddess)|AtíraTemplate:Hamza]] [Script error: No such module "IPA".], an epithet of the Earth goddess of the Pawnee people. AtíraTemplate:Hamza is the wife of the creator god, Tirawa, and goddess of Earth and the evening star.[3][14] The official naming citation was published by the Minor Planet Center on 22 January 2008 (M.P.C. 61768Script error: No such module "Check for unknown parameters".).[15]

See also

References

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  6. ↑ a b c d Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "citation/CS1".
  8. ↑ Script error: No such module "Citation/CS1".
  9. ↑ Script error: No such module "Citation/CS1".
  10. ↑ Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".

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External links

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