Ariel (Uranus I)

Ariel This image of Ariel shows a world pock-marked with craters. Across its surface long rift valleys extend. Ariel has canyons similar to those on Mars, with canyon floors that appear to have been smoothed by a fluid. The fluid could not have been water because water acts like steel at these temperatures. The flow marks might have been made by ammonia, methane or even carbon monoxide.

(Credit Calvin J. Hamilton)