For a long time there's been an understanding in SETI that rocky planets aren't the most likely places for life to arise.<p>That is, a rocky planet contains very little water to begin with, gets cooked in the early days and is very lucky to get rehydrated by comets and not lose the water it gets.<p>Get outside the frost line and generic bodies (outer solar system, cometary, interstellar) can be 50% water.<p>Gas giant moon systems generically have tide-locking situations such as the Io-Europa-Ganymede resonance. Something that gets cooked a bit less than Io or a bit more than Europa could easily be habitable. Tide locking could be relevant close to (common!) red or brown dwarfs. For that matter, geothermal energy is a generic heat source that probably produces liquid water in many outer solar system bodies, probably even Pluto.<p>It's not so clear how geothermal + tides would support the development of higher life, but the most common environments for simple life are clearly outside the frost line. Interplanetary species able to change the form of their bodies would likely learn to colonize the available locations in preparation for becoming interstellar.