Question

Are there such things as starless "rogue" planets? If so, are they of any interest to astrobiology?

In theory, yes. Starless planets could exist, wandering through space dark and invisible to our telescopes. According to planetary scientist David Stevenson in a 1999 issue of Nature, such planets could have been ejected from young solar systems by the competing gravitational forces of larger planets and the sun. These nomadic worlds could, in theory, maintain conditions for life if a thick atmosphere was present to trap heat and maintain liquid water. Without the sun as an energy source, life on these worlds would have to depend on geothermal energy (volcanism) for the warmth necessary to construct and maintain organic compounds. Of course, these planets would eventually cool off with the slow loss of geothermal activity over a couple billion years. Past an age of volcanic activity, these rogue planets would no longer be able to sustain life. While the idea of nomadic, life-bearing planets may be a captivating one, the detection of such entities would be virtually impossible. These planets may emit a weak whisper of radio signal, but they would remain invisible to our telescopes unless they happen to pass in front of another star or bright object.
March 11, 2002