Could TRAPPIST-1 Host Alien Life? Two Planets in the Solar System Could Hold Onto Their Atmospheres

The TRAPPIST-1 solar system and what form of water each planet's surface could hold. NASA/JPL

Arguably the most exciting solar system studied this year—beyond our own, of course—could fulfill an important likely prerequisite for finding life beyond Earth, according to a new paper published in the journal Proceedings of the National Academy of Sciences.

The paper looks at what sort of atmosphere could surround each of the seven rocky, Earth-sized planets that orbit a star known as TRAPPIST-1. An atmosphere is basically a giant gas blanket that can help protect a planet from the barrage of dangerous radiation that can otherwise come from a star. But stars also produce what astronomers call stellar wind, a blast of charged particles traveling as fast as 1000 miles per second, which can degrade that atmosphere.

So the scientists behind the new paper decided to model what kind of stellar wind the TRAPPIST-1 star might produce and how it might affect its seven planets. Creatively, those planets are named TRAPPIST-1b through TRAPPIST1-h, in alphabetical order with b closest to the star and h farthest away. (Skipping the letter a is not a fluke, it's often purposefully skipped in exoplanet naming because it's sometimes used to refer to the star itself.)

Three of those planets, TRAPPIST-1e, f, and g, are particularly intriguing to astronomers because they're located in what astronomers call the habitable zone. That's the ring around a star that is far enough away for water not to boil off a planet's surface, but close enough that liquid water could exist, not just ice.

Stellar wind is most powerful closer to a star, but the scientists were still surprised to discover that TRAPPIST-1b, the closest planet, is within the so-called critical surface, which the authors write means that it could interact magnetically with the star, a highly unusual phenomenon.

Read more: Panspermia: Mysterious Asteroid Oumuamua Could Be a Galactic Bus Carrying Life Between Solar Systems

But for those with hopes of finding life beyond Earth, things got really interesting at TRAPPIST-1g and h. The authors caution that their calculations may not hold up, since so many factors influencing stellar wind still aren't very well understood in the TRAPPIST-1 system.

Nevertheless, they suggest that both TRAPPIST-1g and h should be able to cling to their atmospheres despite the onslaught of stellar wind. That means TRAPPIST-1g, nestled in the habitable zone, may possess not one but two likely criteria for hosting alien life.