Usually when we talk about outer planet moons with oceans, we’re looking at Jupiter’s Europa, and Saturn’s Enceladus. But evidence continues to mount for oceans elsewhere. In the Jupiter system alone, Callisto and Ganymede are likewise strong candidates, while Saturn’s Titan probably has a layer of liquid water. Pluto’s moon Charon may possess an ocean of water and ammonia, to judge from what appears to be cryovolcanic activity there. At Neptune, Triton’s high-inclination orbit should produce plenty of tidal heating that may support a subsurface ocean.
Let’s pause, though, on another of Saturn’s moons, Dione. Here we have evidence from Cassini that this world, some 1120 kilometers in diameter and composed largely of water ice, has a dense core with an internal liquid water ocean, joining Enceladus in that interesting system. But what engages us this morning is not liquid water but a set of straight, bright stripes discovered on the surface and discussed in a new paper from Alex Patthoff (Planetary Science Institute) and Emily Martin (Center for Earth and Planetary Studies, Smithsonian Institution).