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When our sun expands earthlings, if still alive, will have to leave. The Galilean moons offer a lot of water but we would also need land. As far as I can tell there will be no land for earthlings to live on when the oceans of these moons melt. Is anyone aware of land masses on these moons and if so how large?

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    $\begingroup$ We will still have boats to float! Your universe can't get rid of us that easily. $\endgroup$ – J. Chomel May 24 '18 at 8:29
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    $\begingroup$ To make this a sllghtly more concrete question perhaps more suited to this forum, you could ask "What is known about the topography of the rocky cores of the Galilean Moons? Specifically, do they touch the ice crust anywhere?" which is more or less the same question, but couched in more "sciency" terms. I don't know the answer, but I'd be interested if anyone does. Incidentally, the same question makes sense for Ceres and Titan, at least. $\endgroup$ – Steve Linton May 24 '18 at 8:42
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We're not even sure the Galilean moons will still be orbiting Jupiter in 5 billion years. They probably will, but it's hard to say with certainty. It's difficult to model their orbital stability over that long a time-frame.

But in the spirit of your question, it takes much more than oceans and land to make a planet or moon livable. You also need atmosphere, proper gravity (Jupiter's moons have very low gravity) and the right mix of elements. If, somehow, one of the Galilean moons had continents, it's "ocean water" would be full of ammonia and other elements and we'd find it both stinky and likely toxic.

But the answer to your question is no, there are no continents. The ice/water to silicate and metal-oxide ratio for the Galilean moons is much too high for it to ever form continents, and even if it could, a moon that light would have some difficulty retaining it's oceans. Some would boil of into an atmosphere and with that low gravity, the atmosphere would be stripped from the moon over time.

From a practical standpoint, there aren't any good options for mankind to move to in 1-4 billion years. Terra-forming mars is possible but difficult and only a temporary solution. In time the Sun would get too hot for Mars as well. Titan is an interesting option because it has about the right atmospheric pressure. That's actually very useful, though living on Titan would be kind of dreary. It's under a constant thick blanket of clouds.

The good news is, there's a lot of time to find a solution and living in space doesn't require living on the surface. Living under the surface of an icy body (like Pluto) would be workable too. In fact, there's several advantages to living inside an icy world rather than trying to construct one where we live on the surface. Much less work to set it up.

If someone wants to move this to world-building, feel free, but I felt the question was asked in good faith.

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