We study the prospects for life on planets with subsurface oceans, and find that a wide range of planets can exist in diverse habitats with ice envelopes of moderate thickness. We quantify the energy sources available to these worlds, the rate of production of prebiotic compounds, and assess their potential for hosting biospheres. Life on these planets is likely to face challenges, which could be overcome through a combination of different mechanisms. We estimate the number of such worlds, and find that they may outnumber rocky planets in the habitable zone of stars by a few orders of magnitude.
