Scientists now think it's not only possible for life to exist on a planet which isn't in orbit around a star, but that these vagabond planets might be key for spreading life throughout the universe. Experts previously hypothesized that conditions wouldn't have enough gravity to hold water and be too cold and to sustain life. Now they believe that even if a planet is covered in ice, the warm radioactive core can keep enough water liquified under the surface for over a billion years. [New Scientist]