Callisto is Jupiter‘s second largest moon and the fourth of the Galilean moons in terms of distance from Jupiter.

Callisto is slightly smaller Saturn‘s moon Titan, making it the third largest moon in the solar system.

Callisto was discovered in 1610 by Galileo Galilei, the first astronomer to observe Jupiter through a telescope, along with the other three Galilean moons – Io, Europa and Ganymede.

Callisto’s icy, browny-grey surface is covered in bright impact craters, some comprised of large multiple concentric rings.