Moons · Moon of Saturn

Iapetus

3.56 million km from Saturn · Light crosses it in 0.0049 seconds

Across

1,469 km

Vs Earth

12% of Earth

Mass

0.03% of Earth

Open Iapetus in Cosmic Scale

About

Iapetus is Saturn's two-faced moon: its leading side is as dark as coal and its trailing side as bright as snow. A mountain ridge runs around its equator, giving it the look of a walnut.

One side is as dark as coal, the other as bright as snow.

At a glance

Size	1,469 km
Orbits	Saturn, every 79 days
Discovered	1671, Giovanni Cassini
Equatorial ridge	Up to 20 km high

Did you know

1. Cassini noticed in 1671 that he could only see it on one side of Saturn — its dark side was facing him on the other.
2. The dark coating comes from dust swept up in its orbit, which warms the ice underneath until it moves to the bright side.
3. It orbits far out, and its path is tilted, giving the best view of Saturn's rings of any large moon.

Real photo

• Iapetus, with its dark leading side, from Cassini — NASA/JPL/Space Science Institute · source