Mean Radius: 1830 km
Mass: 8.94x1022 kg
Orbital Period: 1.769 Earth days
Rotation Period: 1.769 Earth days
Orbit: 422,600 km from Jupiter
Io one of the four Galilean moons of Jupiter. The other Galilean moons are Ganymede, Callisto, and Europa.
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Few of Io's mountains resemble volcanoes. Instead, Galileo scientists believe that the mountains are formed when blocks of Io's crust are uplifted along thrust faults. Angular mountains are thought to be younger, while older mountains have more subdued topography.
A cliff slumps outward in these high-resolution views that NASA's Galileo spacecraft captured of the edge of a mountain named Telegonus Mensa on Jupiter's moon Io.
When Galileo flew near the south pole of Io in October 2001, scientist stargeted this cliff to study the process of erosion. Water and wind cause most erosion on Earth, but Io has neither surface water nor an atmosphere. The cliff is slumping due to gravity.