A small satellite of Jupiter, distance 7 504 000 km; also known as Jupiter XVIII. It orbits every 130.0 days at an inclination of 43° to the planet’s equator and is about 8 km in diameter. Themisto was first seen in 1975 but not confirmed until 2000, in both cases from ground-based observations. It gives its name to the Themisto prograde irregular group of Jovian satellites, of which it is so far the sole member.