Exomoons May Be The Newest Target For Finding Alien Life

An artist’s illustration of a potentially habitable exomoon orbiting a giant planet in a distant solar system. NASA GSFC: Jay Friedlander and Britt Griswold

Whether there is life elsewhere in the universe is a constant question in astronomy. The discovery of thousands of exoplanets orbiting distant stars tells us that our situation is likely not unique, but signs of life remain elusive. A new piece of research suggests we should move our attention away from some exoplanets and instead focus on their moons.

Accepted for publication in the Astrophysical Journal, a new study has identified 121 exoplanets that are likely to host natural satellites that could support life. These exomoons are situated in the habitable zone of their respective stars, and while they orbit a gas giant planet, there is a good chance they are rocky and have liquid water on their surface.

“There are currently 175 known moons orbiting the eight planets in our Solar System. While most of these moons orbit Saturn and Jupiter, which are outside the Sun’s habitable zone, that may not be the case in other solar systems,” co-author Stephen Kane, from the University of California Riverside, said in a statement. “Including rocky exomoons in our search for life in space will greatly expand the places we can look.”

Exomoons orbiting gas giants receive light directly from their stars and indirectly from their host planet – this is believed to be a pro-life feature. The ability of exomoons to have life is a complex question. We know that moons in our own Solar System are geologically active thanks to the action of their host planets, but is this property detrimental or favorable to life?

The 121 exoplanets identified have a radius at least three times that of Earth, and they orbit stars similar to our Sun or dimmer. The team believes that if the occurrence rate of these exomoons is similar to what we see in our Solar System, we might be more than doubling the number of places where life could exist.

“Now that we have created a database of the known giant planets in the habitable zone of their star, observations of the best candidates for hosting potential exomoons will be made to help refine the expected exomoon properties," lead author Michelle Hill explained. "Our follow-up studies will help inform future telescope design so that we can detect these moons, study their properties, and look for signs of life."

Moons have become important study grounds for potential life. Europa and Enceladus, orbiting Jupiter and Saturn respectively, are icy moons with a liquid ocean underneath. Life in some shape or form might be there.

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