Planet hunters have identified hundreds of exoplanets, or planets outside our solar system. So far, none seem to support life as we know it.
Most of those worlds are too big and too hot; some are too cold. But many would likely have moons. And just the right moon could be a cradle of alien life, concludes a pair of astronomers.
René Heller of the Leibniz Institute for Astrophysics in Potsdam, Germany, and Rory Barnes of the University of Washington in Seattle created a checklist of what would make a moon livable.
They published the list in the January Astrobiology. No exomoons have been found yet. But when they are, the checklist will help identify which ones E.T. might call home.