Io - Voyager 1

Jupiter's moon Io, with Jupiter in the background

Io
Voyager 1 image of Io against the background of Jupiter's clouds. Io is 3,600 km in diameter, about the size the Earth's Moon. The surface is coated with sulfur compounds, making it six times brighter than the Moon. The brightness variations seen may represent compositional and/or age differences. North is up. (Voyager 1, P-21162) 

Io;
Galilean Satellites
Voyager Missions