A mission to Uranus and Neptune could act as massive gravitational-wave detector
March 13 marks 240 years since William Herschel discovered Uranus. But he wasn't the first to spot the aquamarine ice giant.
Astronomers have found evidence that it rains diamonds on Neptune and Uranus, that Mars' ancient water created opals, and that some exoplanets have clouds full of rubies and sapphires.
