Callisto
Callisto’s surface is described as the oldest and most heavily cratered in the Solar System, almost completely covered with impact craters. It is the third-largest moon in the Solar System and nearly as large as the planet Mercury.
Briefing
Callisto is a moon of Jupiter: the planet’s second-largest, after Ganymede, and the outermost of the four large Galilean moons. It has a diameter of 4,821 km and orbits Jupiter at an average distance of 1.883 million km—about five times farther out than the Moon orbits Earth—and it is visible from Earth with common binoculars.
How we know
Callisto is counted among the Galilean moons discovered in 1610 with one of the first telescopes, placing it among the earliest celestial bodies revealed as worlds in orbit rather than mere points of light. Its surface character—described as almost completely covered with impact craters, without signatures of subsurface processes such as plate tectonics or volcanism—is known through close-up imaging that resolves specific landforms: multi-ring structures, impact craters of varied shapes, and chains of craters called catenae, along with associated scarps, ridges, and deposits.
- Field conditions
- Visible from Earth with common binoculars; it appears as a small point of light near Jupiter.
