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Suppose I want to climb the tallest mountain on each of the four Galilean satellites. Is it known what they are?

Io has one of the most spectacularly tall mountains in the solar system, Boösaule Montes, at about 18 km from base to peak.

But googling turns up almost nothing specific on Europa, Ganymede, and Callisto. I'm having a hard time figuring out whether this is just because they don't have as much surface relief, so they aren't as much fun to discuss, or if there is actually no data on their topography. How do we know, for example, how tall Boösaule Montes is? Since we've never inserted anything into orbit around these bodies, I assume there is no radar data. Is our knowledge from estimates based on the lengths of shadows?

My guesses were that since Callisto and Ganymede are heavily pocked with craters, their highest mountains would be the ramparts of crater rims. Maybe on Callisto it would be one of the concentric rims of the Valhalla system. Europa is thought to be extremely smooth, which might make it difficult to determine much about its topography.

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    $\begingroup$ I believe the outer surface of the 3 other moons is all ice, which will lead to a rather bland area. But I suspect we just don't know. We haven't had a Cassini type mission to Jupiter, Galileo really had nothing as far as this kind of detail to really understand this level of geography. $\endgroup$ – PearsonArtPhoto Jun 22 '15 at 1:27
  • $\begingroup$ It's also a question of how you measure where the base is. After all, you can't take the sea level as on earth. $\endgroup$ – Rikki-Tikki-Tavi Jun 24 '15 at 13:10
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Mountains on Europa, Callisto, and Ganymede aren't particularly well known. The moons are made of ice, which tends to be flat, and haven't had a mission that could really measure their terrain. This is partially a function of relatively few flybys, 5 of Ganymede, 8 of Callisto, 12 of Europa, and 6 of Io. Io was easy to identify features, but there simply isn't enough surface features to use the data from the other moons to identify terrain.

As for Io, it has a much more diverse altitude, not being covered in ice, and having volcanic activity. It has high spots that are measured by stereo images and shadows. Neither of these methods is particularly accurate, but they do work to getting an estimate of the height compared to the surrounding terrain. In fact, they have given a wide range for the mountains of Io. Boösaule Montes, for instance, has an uncertainty of 700m to it's height (17.5-18.2 km)

For reference, the best altitude information from orbit comes from a laser altimeter (MOLA for Mars), and the second best from RADAR, neither of which has been tested at Jupiter. Next best is a specific stereo image, but that will only measure relative heights, and not absolute heights.

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