140 Siwa

140 Siwa

Discovery
Discovered by	Johann Palisa
Discovery date	October 13, 1874
Designations
Minor planet category	Main belt
Orbital characteristics
Epoch December 31, 2006 (JD 2454100.5)
Aphelion	497.275 Gm (3.324 AU)
Perihelion	320.360 Gm (2.141 AU)
Semi-major axis	408.817 Gm (2.733 AU)
Eccentricity	0.216
Orbital period	1650.076 d (4.52 a)
Average orbital speed	17.80 km/s
Mean anomaly	156.165°
Inclination	3.187°
Longitude of ascending node	107.292°
Argument of perihelion	197.230°
Physical characteristics
Dimensions	109.8 km
Mass	1.4×1018 kg
Surface gravity	0.0307 m/s²
Escape velocity	0.0580 km/s
Rotation period	34.407 h
Temperature	~168 K
Spectral type	C-type asteroid
Absolute magnitude (H)	8.34

140 Siwa /ˈʃiːwə/ is a large and dark main-belt asteroid that was discovered by Austrian astronomer Johann Palisa on October 13, 1874, and named after Šiwa, the Slavic goddess of fertility.

The Rosetta comet probe was to visit Siwa on its way to comet 46P/Wirtanen in July, 2008. However, the mission was rerouted to comet 67P/Churyumov-Gerasimenko and the flyby had to be abandoned.

Attempts to measure the rotation period of this asteroid have produced inconsistent results ranging from 14.7 to 32 hours. Photometric observations of this asteroid at the Organ Mesa Observatory in Las Cruces, New Mexico during 2010 gave an irregular light curve with a period of 34.407 ± 0.002 hours and a brightness variation of 0.05 ± 0.01 in magnitude.

A 2004 study of the spectrum matched a typical C-type asteroid with typical carbonaceous chondrite makeup. There are no absorption features of mafic minerals found. The classification was later revised to a P-type asteroid.