Published on February 13th, 2012 | by Yellow Magpie2
Umbriel Uranus’s Blue Moon
Uranus’s Moon Umbriel
A dark, somewhat blue sphere, is on a continuous journey around the Icy Giant, Uranus. Despite being photographed up close once and the great distance of over two billion kilometres that separates us – we have quite a good picture of what the world of Uranus’s moon Umbriel looks like.
Umbriel, the darkest of all the Uranian moons was named after a character in the poem The Rape of the Lock by Alexander Pope.
Uranus’s Moon Umbriel: A Sub-Zero World
Taking just over four days to complete one trip around Uranus, Umbriel orbits the planet at a distance of 266,000 kilometres (165,000 miles). Uranus’s moon Umbriel is a very cold world with an average surface temperature of minus 198 degrees Celsius (minus 324 degrees Fahrenheit).
Like many other moons in the Solar System, including our own Moon, Uranus’s moon Umbriel is tidally locked. This means that one side continually faces Uranus while the other is always pointing away from the planet.
Uranus’s moon Umbriel is comprised mostly of ice though it is thought to have rocky core and an icy mantle. The density of Umbriel indicates that the moon is comprised of 60 per cent water ice and 40 per cent non-ice. The non-ice component is thought to be a combination of rock and carbonaceous material.
Uranus’s moon Umbriel’s orbit resides completely within the magnetsphere of the planet which means the moon is subject to magnetsopheric plasma which has resulted in the darkening of its trailing hemisphere.
Like Oberon, Uranus’s Umbriel has an extraordinarily extreme seasonal cycle. The poles of the moon spend 42 years in either complete darkness or continuous sunlight.
Presence Of Carbon Dioxide
Carbon dioxide has been observed to be present on the moon’s surface. Although its origins are not fully understood several possible hypotheses have been offered as an explanation. One is that the carbon dioxide is being formed through either organic material or carbonates being bombarded by either charged particles or ultraviolet radiation emanating from the Sun.
The second explanation is that primordial carbon dioxide once trapped in the ice is escaping from Uranus’s moon Umbriel.
Uranus’s Moon Umbriel: A Blue Moon
Uranus’s moon Umbriel’s dark surface reflects only about half as much light as Ariel which is of a similar size. The surface of the moon has a blue tint while sites of fresh impacts have a much stronger blue colour. The leading hemisphere appears to be redder than the trailing hemisphere.
The red colour may be attributed to weathering from a combination of tiny meteorites known as micrometeorites and charged particles from Uranus’s magnetosphere striking the surface.
As of yet, no canyons, or chasmata, have been discovered on the surface of Uranus’s moon Umbriel. This is chiefly because of the poor quality of the images provided to scientists. The only geological features found so far have been craters. Many of these craters have peaks at their centres.
It is thought to have gotten its dark appearance from heavy impacts with comets and asteroids. In fact, the moon is the second most heavily cratered satellite in the Uranian system after Oberon. The largest of its craters measures an impressive 210 kilometres (130 miles) across.
The most prominent of all the craters on Uranus’s moon Umbriel is Wunda crater. Measuring 131 kilometres (81 miles) across its basin it is very bright and creates a highly visible contrast next to the dark surface of the moon.
Formation And Future
Like the other Uranian moons, Umbriel is believed to have been born out of an accretion disc either left over after the formation of Uranus or after the likely impact that gave Uranus its bizarre tilt. This process is thought to have taken several thousand years to complete.
In its past, Uranus’s moon Umbriel may have had a liquid water ocean at the boundary between the icy mantle and the rocky core. However, this liquid ocean, if it had existed, would have long since frozen.
Uranus’s moon Umbriel has only been photographed up-close once by a space probe during a fly-by. In 1986, on its way to the far reaches of the Solar System and beyond, Voyager 2 mapped roughly 40 per cent of the surface of Uranus’s moon Umbriel.
The Voyager probe is the only spacecraft that has been in close proximity to the moon. No other missions have been planned to visit the moon in the foreseeable future.
Highly Recommended Reading
Check out Yellow Magpie’s Uranus: The Coldest Ice Giant for more insight into the largest planet in the Solar System.
You may also like to take a gander at The Solar System And Beyond: A Guide To The Cosmos.
Cosmos is a highly recommended book. It contains large, full-page pictures of the asteroids and writing on the subject by the highly competent author, Giles Sparrow.
For people living in Ireland or the United Kingdom, you can access: Cosmos from here.
For those who live in Canada, you can obtain: Cosmos here.
For Germany: Cosmos.
For France: Cosmos.