Life on lonely planets

Really lonely, on planets that don't even have suns.

Astronomers have never spotted a rogue planet with certainty, butcomputer simulations suggest that our galaxy could be teeming with them. Slingshotted out of their planetary system by the gravity of a bigger planet, these lone worlds zoom far from their parent suns, slowly freezing in the cold of outer space. Any water fit for life would freeze, too. Yet in a paper submitted to The Astrophysical Journal Letters, planetary scientists Dorian Abbot and Eric Switzer of the University of Chicago in Illinois suggest that a rogue planet could support a hidden ocean under its blanket of ice, kept warm by geothermal activity.
They call such a world a Steppenwolf planet after a novel by the German-Swiss author Hermann Hesse, because "any life ... would exist like a lone wolf wandering the galactic steppe." If Steppenwolf planets do exist, there's a chance that some of them could be lurking in space between Earth and nearby stars. If so, they might be a more realistic human destination for the search of alien life than another planetary system, which would be at least several light-years away. There is even a chance—albeit very small—that a Steppenwolf planet crashing into our solar system billions of years ago was the origin of life on Earth.