Planetary Geology Seminar lecture - Uranus & Neptune

11/12/98 - H. D. Maher Jr.

Uranus: moons characterized by diversity independent of size and position. Why?

• Miranda
  • small 470 km in diameter, yet very complex surface, bimodal character
  • amazing image of fault scarps, all normal, indicates global expansion. Why concentrated into one rift system and not distributed?
  • distinctive V-shaped fracture patterns.
  • inhomogenous and incomplete differentiation.
  • energy source? past resonance?
• Ariel
  • much more resurfacing, global graben system, flows.
  • ammonia and water-ice crust.
  • unusual crater size distribution
  • source of energy?
• Umbriel
  • crater distribution that is similar to lunar highlands, lack of tectonic activity.
  • darkest of moons (aging process)
• Titania
  • largest moon, half the earth's moon, similar in Oberon in size but quite different in terms of surface appearance.
  • fewer and smaller craters than Umbriel and Oberon, more like Ariel
  • near global network of grabens with relief of 2-5 km. Younger than most of the cratering.
• Oberon
  • crater saturation, up to 100 km size, similar to lunar highlands.

Neptune: also has ring system, far fewer satellites.

• Triton
  • comparable in size to earth's moon and to Io
  • methane and N2 ices identified at surface, no evidence of water-ice yet.
  • unusual orbital parameters.
  • polar ice cap, global fracture system (triple bands?), Cantaloupe Terrain.
  • crater density similar to that of Lunar Maria, smooth 'volcanic' plains.
  • eruption plumes of active volcanoes, geysers? Sublimation T of N2 pretty low!

Below are photos of a fault scarp 2-5 km high on tiny Miranda!

Once again, diversity of surface activity on these outer moons is surprising.