NOORDWIJK, THE NETHERLANDS — Life might arise in the darkest of places: the moon of a planet wandering the galaxy without a star.
The gravitational tug-of-war between a moon and its planet can keep certain satellites toasty enough for liquid water to exist there — a condition widely considered crucial for life. Now computer simulations suggest that, given the right orbit and atmosphere, some moons orbiting rogue planets can stay warm for over a billion years, astrophysicist Giulia Roccetti reported March 23 at the PLANET-ESLAB 2023 Symposium. She and her colleagues also report their findings March 20 in the International Journal of Astrobiology.
“There might be many places in the universe where habitable conditions can be present,” says Roccetti, of the European Southern Observatory in Garching, Germany. But life presumably also needs long-term stability. “What we are looking for is places where these habitable conditions can be sustained for hundreds of millions, or billions, of years.”
Habitability and stability don’t necessarily need to come from a nearby sun. Astronomers have spotted about 100 starless planets, some possibly formed from gas and dust clouds the way stars form, others probably ejected from their home solar systems (SN: 7/24/17). Computer simulations suggest that there may be as many of these free-floating planets as there are stars in the galaxy.
Such orphaned planets might also have moons — and in 2021, researchers calculated that these moons need not be cold and barren places.
Unless a moon’s orbit is a perfect circle, the gravitational pull of its planet continually deforms it. Resulting friction inside the moon generates heat. In our own solar system, this process plays out on moons such as Saturn’s Enceladus and Jupiter’s Europa (SN: 11/6/17; SN: 8/6/20). A sufficiently thick, heat-trapping atmosphere, likely one dominated by carbon dioxide, might then keep the surface warm enough for water…
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