128 Nemesis
From Wikipedia, the free encyclopedia
For other uses, see Nemesis (disambiguation).
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Discovery
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| Discovered by | James Craig Watson |
| Discovery date | November 25, 1872 |
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Designations
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| Alternative names | |
| Minor planet category |
Main belt |
| Epoch December 31, 2006 (JD 2454100.5) | |
| Aphelion | 463.605 Gm (3.099 AU) |
| Perihelion | 359.010 Gm (2.400 AU) |
| Semi-major axis | 411.307 Gm (2.749 AU) |
| Eccentricity | 0.127 |
| Orbital period | 1665.175 d (4.56 a) |
| Average orbital speed | 17.89 km/s |
| Mean anomaly | 181.168° |
| Inclination | 6.254° |
| Longitude of ascending node | 76.457° |
| Argument of perihelion | 302.407° |
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Physical characteristics
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| Dimensions | 188.2 km |
| Mass | 7.0×1018 kg |
| Mean density | ? g/cm³ |
| Equatorial surface gravity | 0.0526 m/s² |
| Escape velocity | 0.0995 km/s |
| Rotation period | ? d |
| Albedo | ? |
| Temperature | ~168 K |
| Spectral type | C |
| Absolute magnitude | 7.49 |
128 Nemesis is a very large and very dark main belt asteroid, of carbonaceous composition. It rotates rather slowly, taking about one and half Earth days to complete one revolution. Nemesis is the largest member of the Nemesian asteroid family bearing its name. It was discovered by J. C. Watson on November 25, 1872 and named after Nemesis, the goddess of retribution in Greek mythology. Nemesis is also the name of a hypothetical companion star of the sun.
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