Umbriel (moon) - Composition and Internal Structure

Composition and Internal Structure

Umbriel is the third largest and fourth most massive of Uranian moons. The moon's density is 1.39 g/cm3, which indicates that it mainly consists of water ice, with a dense non-ice component constituting around 40% of its mass. The latter could be made of rock and carbonaceous material including heavy organic compounds known as tholins. The presence of water ice is supported by infrared spectroscopic observations, which have revealed crystalline water ice on the surface of the moon. Water ice absorption bands are stronger on Umbriel's leading hemisphere than on the trailing hemisphere. The cause of this asymmetry is not known, but it may be related to the bombardment by charged particles from the magnetosphere of Uranus, which is stronger on the trailing hemisphere (due to the plasma's co-rotation). The energetic particles tend to sputter water ice, decompose methane trapped in ice as clathrate hydrate and darken other organics, leaving a dark, carbon-rich residue behind.

Except for water, the only other compound identified on the surface of Umbriel by the infrared spectroscopy is carbon dioxide, which is concentrated mainly on the trailing hemisphere. The origin of the carbon dioxide is not completely clear. It might be produced locally from carbonates or organic materials under the influence of the energetic charged particles coming from the magnetosphere of Uranus or the solar ultraviolet radiation. This hypothesis would explain the asymmetry in its distribution, as the trailing hemisphere is subject to a more intense magnetospheric influence than the leading hemisphere. Another possible source is the outgassing of the primordial CO2 trapped by water ice in Umbriel's interior. The escape of CO2 from the interior may be a result of past geological activity on this moon.

Umbriel may be differentiated into a rocky core surrounded by an icy mantle. If this is the case, the radius of the core (317 km) is about 54% of the radius of the moon, and its mass is around 40% of the moon’s mass—the parameters are dictated by the moon's composition. The pressure in the center of Umbriel is about 0.24 GPa (2.4 kbar). The current state of the icy mantle is unclear, although the existence of a subsurface ocean is considered unlikely.

Read more about this topic:  Umbriel (moon)

Famous quotes containing the words composition, internal and/or structure:

    The composition of a tragedy requires testicles.
    Voltaire [François Marie Arouet] (1694–1778)

    The analogy between the mind and a computer fails for many reasons. The brain is constructed by principles that assure diversity and degeneracy. Unlike a computer, it has no replicative memory. It is historical and value driven. It forms categories by internal criteria and by constraints acting at many scales, not by means of a syntactically constructed program. The world with which the brain interacts is not unequivocally made up of classical categories.
    Gerald M. Edelman (b. 1928)

    Vashtar: So it’s finished. A structure to house one man and the greatest treasure of all time.
    Senta: And a structure that will last for all time.
    Vashtar: Only history will tell that.
    Senta: Sire, will he not be remembered?
    Vashtar: Yes, he’ll be remembered. The pyramid’ll keep his memory alive. In that he built better than he knew.
    William Faulkner (1897–1962)