Thetis was a Nereid, one of the daughters of Nereus, the Old Man of the Sea. She was the mother
of Achilles, who has his own asteroid, numbered 588. It was Thetis who dipped her son in the
River Styx to make him invulnerable, but she held him by the heel, and so gave him his
Thetis orbits in the central regions of the main Asteroid Belt, in an orbit that lies close
to the Ecliptic. Thetis' orbit takes it up to 2½ Astronomical Units from the Sun,
and its journey round the Solar System takes just under four years to complete.
Thetis' mean diameter is some 93 kilometres (58 miles), making it very roughly the size
of the island of Rhodes. It absorbs 85% of the sunlight that falls on it, making it a
relatively dark object in comparison with brighter asteroids like Vesta.