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Discovery[1]
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| Discovered by | James Craig Watson |
| Discovery date | November 25, 1872 |
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Designations
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| Named after | Nemesis |
| Alternate name(s) | |
| Minor planet category |
Main belt[1] |
| 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 | 188.16 km[1] |
| Mass | 7.0×1018 kg |
| Mean density | ? g/cm³ |
| Equatorial surface gravity | 0.0526 m/s² |
| Escape velocity | 0.0995 km/s |
| Rotation period | 39 hr[1] |
| Albedo | 0.05[1] |
| Temperature | ~168 K |
| Spectral type | C[1] |
| Apparent magnitude | 10.46 to 13.58 |
| Absolute magnitude (H) | 7.49[1] |
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 (39 hours)[1] 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,[1] 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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