It would not greatly surprise me if, eventually, the percentage of interior-oceaned worlds that produced life was considerably higher than the percentage of rocky, open-oceaned planets that produced life.
Like, the geological record of Earth seems to suggest that long-term life was only just a borderline-viable proposition and that there were several occasions when things could have gone either very wrong (from the perspective of the eventual development of complex life) or very differently.
I do have to wonder though - in a lot of cases these worlds must be like those little self-contained, self-sustained ecosystems that people sometimes make in glass jars, where everything works fine as long as there's an ecological balance, and balances might even be long-term stable, but any kind of upset can cause the entire ecosystem to fall apart rapidly. As much as it wouldn't surprise me to find that a high percentage of these worlds produced life, it also wouldn't surprise me if a high percentage of them turned out to have oceans full of dead organic gunk that was the leftover result of a cascading ecological catastrophe.
I wouldn't be surprised, but it'd be hard to see how intelligent life could develop on those moons and planets, at least intelligent life that could build much of anything. Probably be a bunch of gorgeous/terrifying sea monsters.
Yeah, some tough challenges for anything developing underwater. Their whole technological outlook would start out different to ours and some of the limitations would be really severe (metalworking would be an absolute nightmare to figure out - it took millennia for humans and we had tons of advantages over underwater creatures). There's probably some scope for skipping or rearranging technological progress and I'm sure there's some advantages to starting off underwater too, but I think any intelligent life that started off underwater would probably take more time to progress than a land-based species of similar intelligence.
I think the next NASA remote "rovers" should be mini-subs. Just gotta figure out how to get them under the ice on those moons and how to get them to come back up to transmit back to Earth at regular intervals.
They're not getting back up, not a hope. Ice is going to refreeze over them. The current thinking is that any submersible would need to relay back to the surface. Maybe via cable, maybe via buoys dropped at intervals in the ice that was (somehow) melted on the way down. Those kind of options are challenging but shouldn't actually be too far-fetched if someone manages to solve the main problem of how to melt through kilometres of ice autonomously on another world.
Some thoughts: Do the temperatures and pressures in those oceans support complex organic molecules like kind you'd need for life similar to Earth's?
Yeah, it should be possible. There's estimates of Europa's ice covering that go to 30km (maybe - and likely - more in places). With gravity a bit less than a seventh of Earth's, "surface" pressure (at the top of the ocean where it met the ice covering) would be about the equivalent of the pressure that would be caused by 4km of ice on Earth, or a depth of ~3.7km of water.
Plenty of life at those kinds of depths on Earth. If 30km turns out to be an overestimate (and there's estimates as low as 10km) then "surface" pressure would be significantly lower (by linear proportions, so 15km of ice would result in "surface" pressure equivalent to an ocean depth of ~1.85km on Earth.
You'd get different figures for other worlds, varying by their gravity and depth of their ice covering, but unless they were significantly bigger than Europa or had significantly thicker ice sheets, pressure should be within viable ranges for life.
The next big question is similar, but for complex life, which at least on Earth have a much narrower range of potential conditions (e.g., there are probably no vertebrates in the deepest parts of the Marianas Trench).
This little trooper isn't quite from the deepest parts of the Marianas, but close enough.
