163693 Atira

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163693 Atira
Discovery [1]
Discovered by LINEAR
Discovery site MRO
Discovery date 11 February 2003
MPC designation 163693 Atira
Named after
(goddess of the Pawnee)[2]
2003 CP20
Atira (Apohele or IEO) · NEO · Venus-crosser
Orbital characteristics[1]
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)
Eccentricity 0.32214
0.64 yr (233.0 d)
Inclination 25.619°
Earth MOID 0.207224 AU (31.0003 Gm)
Jupiter MOID 4.42023 AU (661.257 Gm)
Physical characteristics
Dimensions 2.7±1 km[3]
1.63 km (calculated)[4]
2.9745 h[a]
0.20 (assumed)[4]

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.[2]

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).[1][5][6] 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),[7] 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).[1]

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).[4] 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.[2][8]

See also[edit]


  1. ^ a b Pravec (2003) web: rotation period 2.9745±0.0006 hours with a brightness amplitude of 0.36 mag. Summary figures at Collaborative Asteroid Lightcurve Link (CALL) for (163693) Atira
  1. ^ a b c d e "JPL Small-Body Database Browser: 163693 Atira (2003 CP20)" (2015-05-06 last obs.). Jet Propulsion Laboratory. Retrieved 25 March 2016. 
  2. ^ a b c "163693 Atira (2003 CP20)". Minor Planet Center. Retrieved December 2015. 
  3. ^ a b "(163693) Atira – PHYSICAL INFORMATION". NEODyS: Near Earth Objects – Dynamic Site. Retrieved December 2015. 
  4. ^ a b c d "LCDB Data for (163693) Atira". Asteroid Lightcurve Database (LCDB). Retrieved December 2015. 
  5. ^ Wm. Robert Johnston. "Names of Solar System objects and features". Archived from the original on 12 April 2010. Retrieved 2010-04-03. 
  6. ^ 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. 
  7. ^ "NEO Groups". Jet Propulsion Laboratory. Retrieved December 2015. 
  8. ^ "www.godfinder.org". www.godfinder.org. Archived from the original on June 9, 2014. Retrieved 2014-06-15. 

External links[edit]