Does Uranus' Moon Ariel Have a Hidden Ocean?
View larger. | This is a moon of the planet Uranus, called Ariel, as seen by the only spacecraft to have visited Uranus. Traveler 2 In 1986, a new study suggested that Ariel might be one of several moons of the giant planets in the outer solar system with a subsurface ocean. Image via NASA/JPL-Caltech/