Answer:
Ganymede has a very thin atmosphere and its average surface temperature is -171 degrees F. so it would obviously require an external suit for protection from the elements and to store, filter and convert oxygen to a form breathable by humans, as Ganymede has a largely oxygen composed atmosphere but not in the form or density humans need. For a size comparison, here is a picture of Earth, our moon and Ganymede all side by side. Ganymede is the medium sized of the three in the bottom left-hand corner.
It has a liquid-iron core which provides a small magnetosphere for protection from radiation but Jupiter’s magnetosphere substantially over powers it. The surface gravity is slightly more than a tenth of Earth’s, so I’d personally enjoy the lesser effort required to move my big bones around. As with most moons, Ganymede is tidally-locked, meaning that one side always faces Jupiter and one side always faces outward. This means a few things but most importantly to your question, it means that Jupiter’s gravity pulls hard enough, continuously on the same side to provide some geothermal activity. Those warm spots would provide opportunities for energy gathering and further scientific study.
Maybe the most important part of Ganymede’s potential habitability is that we believe it has a huge underground salt-water ocean which could be used in many ways to sustain a colony. The only obstacle is that much and/or all of the technology we are talking about that would be required, is not yet in existence.
