Tethys
Moon· orbits Saturn
Tethys is a mid-sized, ice-rich moon of Saturn marked by the huge Odysseus impact crater and the vast Ithaca Chasma canyon.
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Key facts
Mass
6.17 × 10²⁰ kg
0.00841 Moon masses
Radius
531 km
31% of our Moon's radius
Surface gravity
0.146 m/s²
1% of Earth's gravity
Day length
45.31 hours
Orbit around Saturn
1.89 Earth days
Science
Physical
- Mass
- 6.17 × 10²⁰ kg · 0.00841 Moon masses
- JPL / IAU mean radii; spacecraft-tracked GM where measured
- Radius
- 531 km · 31% of our Moon's radius
- JPL / IAU mean radii; spacecraft-tracked GM where measured
- Density
- 984 kg/m³ · 0.98× water
- Computed from mass and radius
- Surface gravity
- 0.146 m/s² · 1% of Earth's gravity
- Computed from mass and radius
- Escape velocity
- 394 m/s · 4% of Earth's escape velocity
- Computed from mass and radius
Orbit around Saturn
- Distance from Saturn
- 295,000 km
- From JPL orbital elements
- Orbital period
- 45.31 hours
- From JPL orbital elements
- Eccentricity
- 0.001
- From JPL orbital elements
- Inclination to Saturn's Laplace plane
- 1.10 °
- From JPL orbital elements · The Laplace plane is the one a moon's orbit precesses about: close in it is the planet's equatorial plane, the plane of the rings, and further out it tilts toward the planet's own orbit.
Rotation
- Rotation period
- 45.31 hours
- Tidal locking
- Tidally locked to its parent
Temperature
- Mean
- 86 K (-187 °C)
Composition
- Bulk composition
- Almost pure water ice with very little rock — one of the least dense moons known.
Radiation & temperature
- Insolation
- 0.0112 S⊕ · 1% of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Bond albedo
- 0.70 · reflects 70% of incoming sunlight
- Equilibrium temperature
- 67 K (-206 °C)
- Computed from albedo + distance from the Sun (airless black body)
- Measured mean temperature
- 86 K (-187 °C)
- Greenhouse warming
- +19 K
- Measured temperature minus the airless equilibrium — the greenhouse effect
Discovery & history
- Discovered
- March 21, 1684
- By
- Giovanni Domenico Cassini
- Method
- Visual discovery (telescopic)
- Name
- Tethys, a Titaness of the sea in Greek myth.
Giovanni Cassini discovered Tethys in 1684 from the Paris Observatory. A ball of nearly pure water ice, it carries the huge Odysseus impact basin and Ithaca Chasma, a canyon system stretching most of the way around the moon.
Images
Images from open archives · credit shown per image