Callisto
The second largest of Jupiter's moons, Callisto 's mass is roughly a third of that of Mercury, but is similar in size. It's radius is about 2400 km.
Unlike Io, Callisto is almost entirely covered with craters. It has changed very little in about 4 billion years. It is the second largest of Jupiter's moons, and is made up of ice and rock. Callisto has an atmosphere made up of carbon dioxide. Plants might do well there, but humans wouldn't!