Iapetus
Moon· orbits Saturn
Iapetus is Saturn's two-faced moon: one hemisphere is as dark as coal, the other as bright as snow, and a strange ridge of equatorial mountains circles much of the body.
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Key facts
Mass
1.81 × 10²¹ kg
0.0246 Moon masses
Radius
734 km
42% of our Moon's radius
Surface gravity
0.224 m/s²
2% of Earth's
Day length
79.3 days
Orbit around Saturn
79.33 Earth days
Science
Physical
- Mass
- 1.81 × 10²¹ kg · 0.0246 Moon masses
- Radius
- 734 km · 42% of our Moon's radius
- Density
- 1,089 kg/m³ · 1.1× water
- Surface gravity
- 0.224 m/s² · 2% of Earth's
- Escape velocity
- 573 m/s · 5% of Earth's
Orbit around Saturn
- Distance from Saturn
- 3,076,018 km
- Orbital period
- 79.3 days
- Eccentricity
- 0.028
- Inclination
- 7.60 °
Rotation
- Rotation period
- 79.3 days
- Tidal locking
- Tidally locked to its parent
Temperature
- Mean
- 115 K (-158 °C)
Composition
- Bulk composition
- Mostly water ice with rock; one hemisphere is coated in a thin, very dark, organic-rich dust.
Radiation & temperature
- Insolation
- 0.0112 S⊕ · 1% of the sunlight Earth receives
- Bond albedo
- 0.20 · reflects 20% of incoming sunlight
- Equilibrium temperature
- 86 K (-188 °C)
- Measured mean temperature
- 115 K (-158 °C)
- Greenhouse warming
- +29 K
Discovery & history
- Discovered
- October 25, 1671
- By
- Giovanni Domenico Cassini
- Method
- Visual discovery (telescopic)
- Name
- Iapetus, a Titan of Greek myth, father of Prometheus and Atlas.
Iapetus, found by Cassini in 1671, is the Solar System's great two-faced world: one hemisphere is as dark as coal, the other as bright as snow. Cassini correctly reasoned it must keep one face toward Saturn, and a strange equatorial ridge gives it the outline of a walnut.
Images
Images from open archives · credit shown per image