The third largest satellite of the solar system, Callisto is almost the size of Mercury. This satellite orbiting Jupiter was discovered by Galileo Galilei in 1610. Its surface is rocky and covered with ice, shaped by the impacts of comets and asteroids for about 4 billion years. Scientists believe that Callisto, like Europa, may have a vast ocean beneath its surface.

Much of our knowledge about Callisto is based on data from NASA's Galileo spacecraft, which explored Jupiter and its moons between 1995 and 2003. The spacecraft acquired this image of Callisto in May 2001, and two years later, the mission came to a dramatic end when it entered Jupiter's dense atmosphere.

Image description:

The satellite Callisto, a spherical, speckled ball, seen from space. Its dark, brownish surface is covered with craters of various sizes and white markings thought to be ice-covered crater tops. The background of the photo is completely black.

 

Credit: NASA/JPL-Caltech/DLR