This eye-catching theory paper asks an elegant but simple question: when dark matter is gravitationaly captured by a planet, can the energy released when it annihalates provide enough heat to make the planet habitable?
The Kepler mission is doing a fantastic job detecting planets around main sequence stars, but what about white dwarfs? Do they have planets? If they do, Agol 2011 suggests that those planets could be detected in ground-based transit surveys.
Assuming that we have acquired the spectrum of a distant terrestrial planet, what would it look like? Would we able to resolve surface features? More excitingly, would we be able to detect biomarkers in the atmospheres of alien Earths?
Could some of the planets ejected from planetary systems during formation harbor potentially habitable subglacial oceans? Abbot & Switzer suggest that they could.