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Discovery[1]
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| Discovered by | Lincoln Near-Earth Asteroid Research |
| Discovery site | Socorro, New Mexico |
| Discovery date | February 11, 2003 |
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Designations
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| Alternate name(s) | 2003 CP20 |
| Minor planet category |
Aten, Atira Venus-crosser |
| Epoch October 22, 2004 (JD 2453300.5) | |
| Aphelion | 146.580 Gm (0.980 AU) |
| Perihelion | 75.149 Gm (0.502 AU) |
| Semi-major axis | 110.865 Gm (0.741 AU) |
| Eccentricity | 0.322 |
| Orbital period | 233.023 d (0.64 a) |
| Average orbital speed | 33.68 km/s |
| Mean anomaly | 20.298° |
| Inclination | 25.618° |
| Longitude of ascending node | 103.952° |
| Argument of perihelion | 252.914° |
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Physical characteristics
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| Dimensions | ~2.0 km |
| Mass | 1.0×1012 kg |
| Mean density | 2.0? g/cm³ |
| Equatorial surface gravity | 0.0003 m/s² |
| Escape velocity | 0.0005 km/s |
| Rotation period | ? d |
| Albedo | 0.10 |
| Temperature | ~323 K |
| Spectral type | ? |
| Absolute magnitude (H) | 16.43 |
Discovered February 11, 2003, by the Lincoln Near-Earth Asteroid Research project's station at Socorro, New Mexico,[1] (163693) Atira (previously named 2003 CP20), was the first asteroid known to have an orbit entirely within that of Earth. Together with 2004 JG6, which has an even smaller orbit, it forms a new subclass of Aten asteroids. Following tradition, the new subclass is named after the first known object in that class, and therefore is known as Atiras.[2][3][4]
Atira takes slightly over 233 days to orbit the Sun. It is a Venus-crosser asteroid, but does not get as close to the Sun as Mercury. With a diameter of about 2 km, it is the largest of the 10 currently known Atiras (Aug 2010) and one of the larger Aten asteroids.
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, 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 Native American god or goddess. Atira is a Pawnee goddess of the Earth and the evening star. [5]
The official citation:
"163693 Atira
Discovered 2003 Feb. 11 by the Lincoln Laboratory Near-Earth Asteroid Research Team at Socorro.
Atira is the Pawnee goddess of Earth and the evening star. This is the first numbered minor planet to have an orbit completely interior to that of the earth."[6]
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