163693 Atira

163693 Atira

Discovery
Discovered by	LINEAR
Discovery site	MRO
Discovery date	11 February 2003
Designations
MPC designation	163693 Atira
Named after	Atira (goddess of the Pawnee)
Alternative names	2003 CP20
Minor planet category	Atira (Apohele or IEO) · NEO · Venus-crosser
Orbital characteristics
Epoch 27 June 2015 (JD 2457200.5)
Uncertainty parameter 0
Observation arc	12.23 yr (4,467 days)
Aphelion	0.9798 AU
Perihelion	0.5023 AU
Semi-major axis	0.7410 AU
Eccentricity	0.3221
Orbital period	0.64 yr (233 days)
Mean anomaly	285.79°
Inclination	25.617°
Longitude of ascending node	103.91°
Argument of perihelion	252.93°
Earth MOID	0.2065 AU
Physical characteristics
Dimensions	2.7±1 km 1.63 km (calculated)
Rotation period	2.9745 h
Geometric albedo	0.20 (assumed)
Spectral type	S
Absolute magnitude (H)	16.3

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 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.

See also

• 2007 EB26 and (434326) 2004 JG6 – members of the Atira (Apohele) group
• Committee on Small Body Nomenclature
• Provisional designation in astronomy § Minor planets

External links

• Discovery Circumstances
• Orbital Information
• Photo
• 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

• Discovery · Orbit diagram · Orbital elements · Physical parameters