>>12409693He means an RTG powered submersible, which is basically a poor Man's nuclear. You can't really use solar panels out past Jupiter, it's just too dark. Obviously under the Europa ice is pitch black no light at all, so you have to rely on a nuclear power source. An RTG has the added benefit of producing quite a lot of heat (which is what actually powers the space craft), which you need to melt/drill your way through the outer shell. Of course there is the ethical question of dumping nuclear reactive material into a foreign and unknown environment that may or may not harbor very fragile life, so I doubt an RTG submersible will ever actually get the green light.
Communication is also a concern, because all that ice is going to block any signals from getting through. You would need to make your submersible capable of autonomous operation for possibly decades without human input, and then have it melt it''s way back to the "surface" again to transmit that data.
All things considered an RTG powered submersible is probably not feasible right now, nor is it ethically conscious.
>>12409718Gannymede and Europa (IIRC Callisto has too much radiation and Io lacks a subsurface ocean), Titan, the moons of Uranus and Neptune, and basically every TNO (Pluto and it's cousins) are possible sights for life.
Not to mention Mars and Venus still haven't been ruled out entirely. They both have really weird atmospheric signatures that are indicative of life. Hell there could hypothetically be life on the gas giants deep under the clouds we can't see or detect.
>>12409725The biggest thing for Mars would be as a hub for system wide travel. Basically Mars colony will service the belt mining operations, and act as a fulcrum for going into or out of the inner solar system. Mars is going to be the Chicago of the system basically, an area of interest that has little intrinsic value other than it's position. Also a lot of Mars colony supporters want to do it just because its THERE.
