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Uranus' Satellites

The Icy Satellites > Uranus' Satellites > Oberon

Oberon :

The discovery of Oberon, along with Titania, is credited to W. Herschel, in 1789. From the point of view of it's general composition (half rock half ice), it does not stand out from the other satellites around Uranus. On the other hand its surface is very different. These different areas that make up the surface, as well as having different albedo's, have different compositions. In Ariel's case, for example, even though there are areas of varying albedo's, the composition of the material does not change, this difference in reflective power is due only to the varying time of exposure to sunlight of the ground

Image by Voyager 2(credit: JPL/NASA)

Distance to Uranus	583 420 km
Period of revolution	13.46 earth days
Diameter	1523 km
Mass (Earth=1)	0.0005072
Density (water =1)	1.64
Composition	Ice water (40-50%), rocks
Albedo	0.20
Temperature on the surface	-188 °C

Oberon's surface can be split into three types of region:

The cratered regions with a relatively uniform albedo
Brilliant rays surrounding some craters : they remind us of the ones seen on the Moon and Callisto. This is clean and shining ice coming from a layer close to the surface.
The darker deposits often seen at the bottom of craters but also is other areas.: these deposits are dirty water, carbon rich water.

It could have a structure similar to that of the lunar oceans created by volcanic flows or material from Oberson's lithosphère, exposed to the surface by erosion caused by impacts. The crater in the centre of the image above is called Hamlet and has shiny peaks.

Given the latter statements, there could be a layer of clean, shiny ice that covers a deeper layer of darker material which would suggest that Oberon has a structure that is at least in part differentiated.

Finally, the surface is essentially cratered which would suggest that if was not globally renewed by the tectonics since the last period of intense bombardment that the bodies in the solar system experienced, which gives Oberon a common feature with Umbriel.

Amusing detail: on the limb at the bottom left of the image there is a mountain of about 6 km heigh! It could be a central peak in a crater.