Callisto: The Ancient, Cratered Moon of Jupiter

Callisto is the second largest of Jupiter’s moons, nearly the size of Mercury.
Its surface is the most heavily cratered in the solar system, preserving ancient impacts.
Unlike its sibling moons, Callisto shows little geological activity.
The giant Valhalla crater spans about 2,500 miles across, one of the largest impact features known.
Callisto’s icy surface is mixed with dark rock, giving it a mottled appearance.
Scientists think a salty subsurface ocean may exist beneath its icy crust.
Because it lacks strong tidal heating, Callisto is considered geologically stable.
Its thin atmosphere is made mostly of carbon dioxide with hints of oxygen.
Callisto orbits farther from Jupiter, avoiding much of the planet’s intense radiation.
This makes Callisto a potential candidate for future human outposts in the outer solar system.