A recent episode of Planetary Radio discussed this. Io could have been a water world as well, once. https://www.planetary.org/planetary-radio/2023-lost-oceans

A recent episode of Planetary Radio discussed this. Io could have been a water world as well, once. https://www.planetary.org/planetary-radio/2023-lost-oceans-and-found-signals https://www.planetary.org/planetary-radio/2023-lost-oceans-a... Rocks can consume a lot of water as well. Their chemistry means they can absorb a lot of water in their mineral structure so water isn’t just about surface oceans but also how much is inside a celestial body as well.