|Discovery date||11 February 2003|
|MPC designation||163693 Atira|
(goddess of the Pawnee)
|Atira (Apohele or IEO) · NEO · Venus-crosser|
|Orbital characteristics |
|Epoch 13 January 2016 (JD 2457400.5)|
|Uncertainty parameter 0|
|Observation arc||4467 days (12.23 yr)|
|Aphelion||0.97975 AU (146.569 Gm)|
|Perihelion||0.50232 AU (75.146 Gm)|
|0.74104 AU (110.858 Gm)|
|0.64 yr (233.0 d)|
|Earth MOID||0.207224 AU (31.0003 Gm)|
|Jupiter MOID||4.42023 AU (661.257 Gm)|
|Dimensions||±1 km 2.7
1.63 km (calculated)
163693 Atira, provisional designation 2003 CP20, is an eccentric, stony asteroid, dwelling in the interior of Earth's orbit. It is classified as a near-Earth object and measures about 2 kilometers in diameter. The body was discovered by the Lincoln Near-Earth Asteroid Research project's station at the U.S. Magdalena Ridge Observatory in Socorro, New Mexico, on 11 February 2003.
It is the namesake and the first numbered body of a new subclass of near-Earth asteroids, the Atira (Apohele) asteroids, which have their orbits entirely within that of Earth and are therefore alternatively called Interior-Earth Objects (IEO). As of 2015, there are only 16 known members of the Atira group of asteroids. 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), which means that they do not approach Earth as close as Atens do in general. The body has an Earth Minimum orbit intersection distance (MOID) of 0.2065 AU (30,890,000 km).
The S-type asteroid orbits the Sun at a distance of 0.5–1.0 AU once every 8 months (233 days). Its orbit is significantly tilted by 26 degrees to the plane of the ecliptic and shows a high eccentricity of 0.32. It has a rotation period of almost 3 hours[a] and an albedo of 0.20, assumed by the Collaborative Asteroid Lightcurve Link (CALL). With a perihelion of 0.50 AU the body also classifies as a Venus-crosser – as Venus orbits the Sun at a distance of 0.72–0.73 AU – but does not get as close to the Sun as Mercury (which orbits at 0.31–0.47 AU).
Knowing that traditionally the first known object in a new class of asteroids will become the name of the new class of asteroids, due consideration was given to the name for (163693). The other classes of near-Earth asteroids are Amors, Apollos, and Atens (as mentioned above), named after a Roman, Greek, and Egyptian god, so a preference was given to a god or goddess beginning with the letter "A". Given (163693) was discovered by the LINEAR program which operates out of the southwestern United States, preference was also given to a name of local origin. The minor planet was named after Atira, a goddess of the Native American Pawnee people. She is the wife of the creator god, Tirawa, and goddess of Earth and the evening star.
- 2007 EB26 and (434326) 2004 JG6 – members of the Atira (Apohele) group
- Committee on Small Body Nomenclature
- Provisional designation in astronomy § Minor planets
- Pravec (2003) web: rotation period ±0.0006 hours with a brightness amplitude of 2.9745 mag. Summary figures at 0.36Collaborative Asteroid Lightcurve Link (CALL) for (163693) Atira
- "JPL Small-Body Database Browser: 163693 Atira (2003 CP20)" (2015-05-06 last obs.). Jet Propulsion Laboratory. Retrieved 25 March 2016.
- "163693 Atira (2003 CP20)". Minor Planet Center. Retrieved December 2015.
- "(163693) Atira – PHYSICAL INFORMATION". NEODyS: Near Earth Objects – Dynamic Site. Retrieved December 2015.
- "LCDB Data for (163693) Atira". Asteroid Lightcurve Database (LCDB). Retrieved December 2015.
- Wm. Robert Johnston. "Names of Solar System objects and features". Archived from the original on 12 April 2010. Retrieved 2010-04-03.
- 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 December 2015.
- "NEO Groups". Jet Propulsion Laboratory. Retrieved December 2015.
- "www.godfinder.org". www.godfinder.org. Archived from the original on June 9, 2014. Retrieved 2014-06-15.
- Discovery Circumstances
- Orbital Information
- Asteroid Lightcurve Database (LCDB), query form (info)
- Dictionary of Minor Planet Names, Google books
- Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend
- Discovery Circumstances – Numbered Minor Planets (160001)–(165000)
- 163693 Atira at the JPL Small-Body Database