Moons of rogue planets habitable for billions of years?

View larger. | Artist’s concept of an Earth-like exomoon orbiting a rogue Saturn-like exoplanet. A new study led by Ludwig Maximilian University of Munich in Germany looked at moons of rogue planets that have been ejected from their planetary systems. The study said these moons could still have oceans and be potentially habitable, if they have hydrogen atmospheres. Image via Frizaven/ Wikipedia (Celestia/GNU General Public License).

• Rogue planets float free in space, not bound to any stars.