Titania (moon) - Origin and Evolution

Origin and Evolution

Titania is thought to have formed from an accretion disc or subnebula; a disc of gas and dust that either existed around Uranus for some time after its formation or was created by the giant impact that most likely gave Uranus its large obliquity. The precise composition of the subnebula is not known; however, the relatively high density of Titania and other Uranian moons compared to the moons of Saturn indicates that it may have been relatively water-poor. Significant amounts of nitrogen and carbon may have been present in the form of carbon monoxide and N₂ instead of ammonia and methane. The moons that formed in such a subnebula would contain less water ice (with CO and N₂ trapped as a clathrate) and more rock, explaining the higher density.

Titania's accretion probably lasted for several thousand years. The impacts that accompanied accretion caused heating of the moon's outer layer. The maximum temperature of around 250 K (−23 °C) was reached at a depth of about 60 kilometres (37 mi). After the end of formation, the subsurface layer cooled, while the interior of Titania heated due to decay of radioactive elements present in its rocks. The cooling near-surface layer contracted, while the interior expanded. This caused strong extensional stresses in the moon's crust leading to cracking. Some of the present-day canyons may be a result of this. The process lasted for about 200 million years, implying that any endogenous activity ceased billions of years ago.

The initial accretional heating together with continued decay of radioactive elements were probably strong enough to melt the ice if some antifreeze like ammonia (in the form of ammonia hydrate) or salt was present. Further melting may have led to the separation of ice from rocks and formation of a rocky core surrounded by an icy mantle. A layer of liquid water (ocean) rich in dissolved ammonia may have formed at the core–mantle boundary. The eutectic temperature of this mixture is 176 K (−97 °C). If the temperature dropped below this value, the ocean would have subsequently frozen. The freezing of the water would have caused the interior to expand, which may have been responsible for the formation of the majority of the canyons. However, the present knowledge of Titania's geological evolution is quite limited.