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Alien life might thrive on the moons of these 121 giant planets

Moons orbiting huge exoplanets may be even better places to live than Earth, scientists say. But there's a catch.

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 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

There's been a lot of excitement in recent years around the discovery of thousands of exoplanets, including dozens that might have the right conditions for supporting life. But new research suggests a number of moons around giant planets beyond our solar system might also be lively places. 

An international team of scientists has identified 121 gas giant planets, each at least three times more massive than Earth, that orbit in the habitable zones of their stars and are each expected to play host to several large moons.

It's thought that most giant planets aren't friendly to life as we know it due to their composition and extremely strong gravity, but they could be orbited by moons that are more similar to Earth. Indeed, Jupiter's moon Europa is a top target in the search for life beyond Earth. The icy world conceals a subsurface water ocean where interesting things might be swimming around. 

In our solar system, the giant planets like Jupiter and Saturn orbit far beyond the habitable region that we enjoy here on Earth, but in other star systems it might be the huge planets that hang out in the "goldilocks zone" where it's not too cold and not too hot.   

"Including rocky exomoons in our search for life in space will greatly expand the places we can look," said Stephen Kane, an associate professor of planetary astrophysics at the University of California, Riverside, in a news release Wednesday. 

Kane is co-author of a paper on the findings that will be published in The Astrophysical Journal

Some speculate that these exomoons might be even more favorable to life than our own home planet. This is because moons don't have to rely solely on energy from a sun, but also receive energy from the planet they orbit in the form of reflected radiation as well as tidal energy. (Tidal forces are what help keep hidden oceans on Europa and Saturn's moon Enceladus from freezing solid.)

"These potentially terrestrial giant satellites could be the perfect hosts for life to form and take hold," reads the paper.

The catch is that no exomoons have been confirmed to exist through direct observation just yet, though some astronomers may have come close. The new research essentially creates a database of the known giant planets in the habitable zone worth a closer look.

"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," said Michelle Hill, a student at the University of Southern Queensland and lead author of the paper.

We may not have to wait for whole new telescopes to be designed to look for the man (or woman or bacterium) in the exomoon. Upcoming next-generation observatories like the James Webb Space Telescope could give us our first direct look at a moon beyond our solar system. 

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