Moon of Saturn
Iapetus
A two-toned moon on a distant, tilted orbit.
Iapetus orbits far from Saturn, taking 79 days per lap on an orbit tilted well away from the ring plane. Even at that distance Saturn has tidally locked it, so its very slow rotation matches its orbit. One hemisphere is dark as coal and the other bright as snow.
How it moves
- Iapetus orbits Saturn every 79.33 days at about 3,560,850 km.
- Its orbit is inclined 14.72 degrees to Saturn's equator, unusual among the large moons.
- It is tidally locked, so one rotation also takes more than 79 days.
- Thanks to that tilted orbit, Iapetus is the only large moon with a good view of Saturn's rings.
Facts
- Mean radius
- 734.3 km
- Mass
- 1.810e+21 kg
- Surface gravity
- 0.224 m/s²
- Rotation period
- 1903.924 hours
- Orbital period
- 79.33 days
- Average orbital distance
- 3,560,850 km
- Eccentricity
- 0.0283
- Discovered
- October 25, 1671, by Giovanni Domenico Cassini
In 1671 Cassini could see Iapetus only on the west side of Saturn and correctly deduced it had a dark side.
Sources: nssdc.gsfc.nasa.gov, ssd.jpl.nasa.gov, ssd.jpl.nasa.gov