128 Nemesis

128 Nemesis is a large 188 km main-belt asteroid, of carbonaceous composition. It rotates rather slowly, taking about one and half Earth days (39 hours) 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.

It is categorized as a C-type asteroid, indicating a primitive carbonaceous composition. Based on IRAS data Nemesis is about 188 km in diameter and is around the 33rd largest main-belt asteroid. The 39 hour rotation period is the second longest for an asteroid more than 150 km in diameter.

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