Cosmic Scale
Iapetus
Moon of Saturn · 3.56 million km from Saturn
How big is Iapetus?
Iapetus is about 1,469 km across.
See Iapetus in 3D, at true scale
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.
At a glance
| Diameter | 1,469 km |
|---|---|
| Mass | 1.81 × 10²¹ kg |
| Diameter compared with Earth | 0.115 × Earth |
| Size | 1,469 km |
| Orbits | Saturn, every 79 days |
| Discovered | 1671, Giovanni Cassini |
| Equatorial ridge | Up to 20 km high |
Good to know
- Cassini noticed in 1671 that he could only see it on one side of Saturn — its dark side was facing him on the other.
- The dark coating comes from dust swept up in its orbit, which warms the ice underneath until it moves to the bright side.
- It orbits far out, and its path is tilted, giving the best view of Saturn's rings of any large moon.