I wonder if there is a thin crust filled with hot swirling liquid, which would explain its "largest in the solar system" magnetosphere (some planets and moons have none).
I like to think that Jupiter and the Jovian moons are better suited for human exploration than Mars. Mars has no magnetosphere or large amounts of water. many of the Jovian moons have water and radiation is minimized due to proximity to Jupiter. Saturn's ice rings can also be transported for humanity's needs.
We could be making space-ship yards and settlements with a mining economy based out of Ganymede and Europa if we weren't busy finding creative and new ways to kill each other. Projects like the ISS are great starts but they're focused on scientific experimentation, not that there's anything wrong with that, but it's been decades and humans haven't even started planning practical applications of all that research. Lots of probes and satellites that cost tens of billions of dollars but not a single plan to establish a Lunar base for civilian and commercial use, or to explore the solar system.
Look at JWT, it is possible to get the political will and financing, even when there is no near-term profit in sight. How much more if humans took risks, made nuclear powered propulsion (despite the risks!) and attempted to make actual pioneering progress! Imagine taking Lunar shuttles being as common as taking an airplane flight to a different continent. The militaries of the world alone would be happy to contribute to his due to the side-effect it has on military technology advancement. It is practical to expect a pace of progress like that in our lifetimes (30-50 years), humans went from flight to moon landing within the span of a normal adult's lifetime.
My observation is that humans have gotten too risk averse and complacent. "It's not about the dog in the fight but the fight in the dog".