128 Nemesis
Nemesis is a large 180 km main-belt asteroid, of carbonaceous composition. It rotates rather slowly, taking about 78 hours to complete one rotation. Nemesis is the largest member of the Nemesian asteroid family bearing its name. It was discovered by J. C. Watson on 25 November 1872, and named after Nemesis, the goddess of retribution in Greek mythology. Nemesis was also the name of a hypothetical companion star of the Sun, which does not exist.
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 77.81‑hour rotation period is the second longest for an asteroid more than 150 km in diameter.
