"It's the most thorough look at exomoon habitability I've seen," says Darren Williams, an astronomer at Penn State Erie who was not involved in the research. “I'm encouraged by the paper that we'll find exomoons in abundance and that a fraction of them could be habitable.”
Astronomers have found about 3,600 confirmed or probable planets orbiting other stars, none of which have the ideal combination of size and temperature to support life. However, more than 150 of them are gas giants in orbits where liquid water could exist, if only it had a solid surface to puddle on. Life might be able to survive on the rocky moons of those Neptune- and Jupiter-like planets.
This bounty of temperate giants led astronomers René Heller of Germany's Leibniz Institute for Astrophysics Potsdam and Rory Barnes of the University of Washington to examine all the factors that determine the habitability of exomoons. Moons are substantially more complicated than planets because they are at the mercy of both their host planet and star: The star pelts them with radiation, and so does the reflection off the top of their planet's gaseous clouds. (Jupiter, for example, reflects about a third of solar radiation that strikes it.) Moons also get squeezed and deformed by the gravitational pull of their massive planetary companions, a phenomenon called tidal heating that supplies yet another source of energy.
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