Umbriel (moon)

**Umbriel** is a moon of Uranus found on October 24, 1851 by William Lassell. It was found at the same time as Ariel.

## Name

The name "Umbriel" and the names of all four moons of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell. Lassell had earlier supported Herschel's 1847 naming scheme for the seven then-known moons of Saturn and had named his newly-found eighth moon Hyperion in accordance with Herschel's naming scheme in 1848. Umbriel is the 'dusky melancholy sprite' in Alexander Pope's _The Rape of the Lock_, and the name suggests the Latin _umbra_, shadow. The adjectival form of the name is _Umbrielian_.

It is also designated **Uranus II**.

## Physical characteristics

So far the only close-up images of Umbriel are from the _Voyager 2_ probe, which made observations of the moon during its Uranus flyby in January, 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.

Umbriel's surface is the darkest of the Uranian moons, and reflects only about half as much light as Ariel, Uranus' brightest moon. It has far more and bigger craters than do Ariel and Titania and is also the least geologically active.  It is mostly made of water ice, with the balance made up of silicate rock, and other ices such as methane.  Methane can break down and form reddish-black organic compounds such as tholins when bombarded by high-energy particles.  Near-IR spectra of Ariel and Umbriel clearly show that water ice dominates the spectra of these objects.

### Craters

Craters on Umbriel are named after many different demons from various mythologies.
|Crater|Named after|
| --- | --- |
|Alberich|Alberich (Norse)|
|Fin|Fin (Danish)|
|Gob|Gob (Pagan)|
|Kanaloa|Kanaloa (Polynesian)|
|Malingee|Malingee (Australian Aboriginal mythology)|
|Minepa|Minepa (Makua people of Mozambique)|
|Peri|Peri (Persian)|
|Setibos|Setebos (Patagonian)|
|Skynd|Skynd (Danish)|
|Vuver|Vuver (Finnish)|
|Wokolo|Wokolo (Bambara people of West Africa)|
|Wunda|Wunda (Australian Aboriginal mythology)|
|Zlyden|Zlyden (Slavic)|

## Other websites

- Umbriel Profile  by NASA's Solar System Exploration
- William Lassell, _Astronomical Journal_ **2** (1851) 70
- AN, **33** (1852) 257/258
- AN, **34** (1852) 325/326
- Uranus and moons  as seen by the VLT in August 2007

## Infobox (planet)

- **name**: Umbriel
- **alt names**: Uranus II
- **adjectives**: Umbrielian
- **image**: PIA00040 Umbrielx2.47.jpg
- **caption**: Umbriel as seen by _Voyager 2_ in 1986
- **discoverer**: William Lassell
- **discovered**: October 24, 1851
- **semimajor**: 266 000 km
- **eccentricity**: 0.0039
- **period**: 4.144 Day, d
- **inclination**: 0.128° (to Uranus's equator)
- **satellite of**: Uranus
- **mean radius**: (0.092 Earths)
- **surface area**: 4 296 000 km<sup>2</sup> (0.008 Earths)
- **volume**: 837 300 000 km<sup>3</sup> (0.0008 Earths)
- **mass**: (2 Earths)
- **surface grav**: Acceleration, m/s<sup>2</sup> (~ 0.023 g-force, g)
- **escape velocity**: km/s
- **rotation**: presumed Synchronous rotation, synchronous
- **axial tilt**: 0
- **magnitude**: 14.5 (V-band, opposition)
- **temp name1**: solstice
- **mean temp 1**:  Kelvin, K
- **max temp 1**: 85 K
- **min temp 1**: ?
- **atmosphere**: no
- **surface pressure**: zero
- **note**: no