We are learning about Uranus, but its distance and lack of much exploration by spacecraft present limits to human observation. Such is the challenge of science, applying ingenuity to gather as much evidence as possible, even when we might want more, and then interpreting what is found. So we can go as far as saying, with a high level of confidence, that ices, of different sorts, including pressurized and unfamiliar forms, make up the bulk of both Uranus and Neptune, the two ice giants. The one companion of Uranus that has been imaged from relatively nearby, by the Voyager 2 spacecraft, is the fifth biggest moon, and closest to the planet, Miranda. It has a surface like no other known object, which includes a cliff that seems to be the tallest in the Solar System—surprising for a moon of modest size. Like Earth, and other objects, it has its own history of geological changes, and so more puzzles to challenge the scientists.