Umbriel
Moon· orbits Uranus
Umbriel is the darkest of Uranus's major moons — an old, uniformly dim, heavily cratered ice world, oddly marked by one bright ring of material ('Wunda').
Open in 3D viewSee Umbriel in the live, interactive 3D map
Key facts
Mass
1.27 × 10²¹ kg
0.0174 Moon masses
Radius
585 km
34% of our Moon's radius
Surface gravity
0.249 m/s²
3% of Earth's gravity
Day length
4.1 days
Orbit around Uranus
4.14 Earth days
Science
Physical
- Mass
- 1.27 × 10²¹ kg · 0.0174 Moon masses
- JPL / IAU mean radii; spacecraft-tracked GM where measured
- Radius
- 585 km · 34% of our Moon's radius
- JPL / IAU mean radii; spacecraft-tracked GM where measured
- Density
- 1,523 kg/m³ · 1.5× water
- Computed from mass and radius
- Surface gravity
- 0.249 m/s² · 3% of Earth's gravity
- Computed from mass and radius
- Escape velocity
- 540 m/s · 5% of Earth's escape velocity
- Computed from mass and radius
Orbit around Uranus
- Distance from Uranus
- 265,986 km
- From JPL orbital elements
- Orbital period
- 4.1 days
- From JPL orbital elements
- Eccentricity
- 0.004
- From JPL orbital elements
- Inclination to the J2000 equator
- 0.10 °
- From JPL orbital elements
Rotation
- Rotation period
- 4.1 days
- Tidal locking
- Tidally locked to its parent
Temperature
- Mean
- 75 K (-198 °C)
Composition
- Bulk composition
- Water ice and rock with a dark, carbon-rich coating of uncertain origin.
Radiation & temperature
- Insolation
- 0.00265 S⊕ · 1/378 of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Bond albedo
- 0.10 · reflects 10% of incoming sunlight
- Equilibrium temperature
- 61 K (-212 °C)
- Computed from albedo + distance from the Sun (airless black body)
- Measured mean temperature
- 75 K (-198 °C)
- Greenhouse warming
- +14 K
- Measured temperature minus the airless equilibrium — the greenhouse effect
Discovery & history
- Discovered
- October 24, 1851
- By
- William Lassell
- Method
- Visual discovery (telescopic)
- Name
- Umbriel, a dusky, melancholy sprite in Pope's 'The Rape of the Lock'.
Lassell found Umbriel on the same night as Ariel in 1851. The darkest of Uranus's large moons, it is an ancient, cratered world marked by a mysterious bright ring nicknamed the 'fluorescent Cheerio'.
Images
Images from open archives · credit shown per image