Steampunk, Space and Aliens

[Johnny1A.2]

Originally Posted by Flyndaran

And you're going to need some hand waving having one habitable moon, let alone three.

A habitable moon isn't a huge stretch. There are issues, but there are issues with habitable worlds generally, and yet Earth exists.

Gas giants sometimes end up close to their stars, you just need to assume that the gas giant in question landed up in the goldilocks zone when the pushing and shoving was done. In a galaxy of stars, that's probably happened many times.

You need bigger bodies than the Galilean satellites, with a higher percentage of rock and metal and less ice. The former you can get by assuming the protostellar cloud was richer in heavy elements than Sol's (probably younger than Sol too). The ice you can assume boiled off during a period during the early formation when the gas giant was really close to the primary.

A bigger problem is tide-lock. You might be able to have a human-habitable (broadly defined) world tide-locked to a gas giant, but it's iffy. So you need to assume the moons orbit further out from their gas giant than the Galilean moons do with Jupiter.

The biggest issue is having three human-habitable moons of one gas giant. That's not probable, to put it mildly, unless there is some natural process producing such that we don't know about. But that might be harnessable as a story-hook. Maybe the moons are the product of terraforming work in the deep past (by human standards), and the terraforming aliens (or whoever) left some powerful plot devices lying around.

(That might even explain part of the schizo-tech aspects of the setting.)