Major Moons of Uranus. New modeling shows that there likely is an ocean layer in four of Uranus' major moons Ariel, Umbriel, Titania, and Oberon. Salty - or briny - oceans lie under the ice and atop layers of water-rich rock and dry rock. Miranda is too small to retain enough heat for an ocean layer. The modeling, detailed in a paper published in the Journal of Geophysical Research, was informed by a re-analysis of data from NASA's Voyager spacecraft. Scientists have long thought that Titania, given its size, would be most likely to retain internal heat, caused by radioactive decay. The other moons had been widely considered too small to retain the heat necessary to keep an internal ocean from freezing, especially as heating created by the gravitational pull of Uranus is only a minor source of heat. https //photojournal.jpl.nasa.gov/catalog/PIA25500