Callisto

Callisto is a large moon of Jupiter. It is about the same size as the planet Mercury. Its surface is packed with craters from long ago. Callisto is one of the oldest and quietest places in the solar system.

A Crater-Covered Moon

Callisto's surface is full of craters. They were made by space rocks crashing into it. Because nothing has changed the surface, the craters have stayed there for billions of years. Callisto has more craters than any other moon or planet we know. Its biggest crater is called Valhalla.

Cold and Quiet

Unlike some other moons, Callisto does not have volcanoes or moving surfaces. It is a cold and still world made of rock and ice. Scientists think there might be a hidden ocean under its surface. Callisto is also far from Jupiter's strong radiation. That could make it a safer place for astronauts to visit one day.

Fun Facts

• Callisto was discovered by Galileo in 1610.
• It is the third largest moon in the solar system.
• The Valhalla crater is over 2,300 miles wide.

Did You Know?

Callisto may be the only one of Jupiter's big moons that people could explore safely because it gets less radiation.