Callisto, too, may have an ocean beneath its icy surface, though this is less certain.

ECONOMIST: Galileo and Jupiter

It will be able to orbit Europa, Callisto and Ganymede individually, hopping from one to another.

ECONOMIST: Galileo and Jupiter

Metallic cores in Europa, Io and Ganymede, but no such core in Callisto.

CNN: Galileo moves on to Europa

When her body was recovered from the Catacomb di San Callisto in 1599, it was apparently found to be miraculously preserved.

BBC: Rome��s most mysterious places

An atmosphere of hydrogen and carbon dioxide on Callisto.

CNN: Galileo moves on to Europa