Two Earth-Sized Planets In The TRAPPIST-1 System May Have Atmospheres, Study Finds

The TRAPPIST-1 planetary system is shaping up to be a good place to look for life beyond our home planet. A recent study revealed two of the TRAPPIST-1 planets could hold onto an atmosphere for up to a billion years at a time. Of these two planets, one is found in the star's habitable zone, which means it has the strongest chances of harboring alien life.

The TRAPPIST-1 system is made up of seven Earth-sized planets that orbit an ultra-cool, M-class, red dwarf star called TRAPPIST-1. This system is located 39.6 light-years (235 trillion miles) from Earth, in the Aquarius Constellation, and has been dubbed "the holy grail" of alien life, due to a number of promising characteristics that could make it habitable.

For instance, of the seven planets in the TRAPPIST-1 system, named TRAPPIST-1b through TRAPPIST1-h, three (TRAPPIST-1e, f, and g) fulfill the two most important prerequisites for the existence of life: they are rocky planets, just like our Earth, and reside in the star's habitable or "temperate zone" — where both temperatures and radiation levels could allow life to spark and even thrive.

In addition, five of the TRAPPIST-1 planets seem to contain water, the Hubble Space Telescope revealed at the end of this summer. According to the Hubble findings, "the outer planets of the system might still harbor substantial amounts of water," NASA explained at the time, in a joint statement with the European Space Agency.

Classified as an ultra-cool red dwarf, TRAPPIST-1 is 2,000 times less bright than our Sun, a G-class yellow dwarf. This means the red dwarf is cool enough for life to "survive on planets orbiting very close to it, closer than is possible on planets in our solar system," shows NASA.

"This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable," details the August 31 statement.

Now, a new study into the seven Earth-like exoplanets of the TRAPPIST-1 system uncovered two of the outer planets, TRAPPIST-1g and h, could be able to retain their atmospheres in spite of the stellar wind produced by their parent star.

A digital illustration of the seven Earth-like exoplanets orbiting the TRAPPIST-1 red dwarf star.
A digital illustration of the TRAPPIST-1 system showing which exoplanets reside in the star's habitable zone.

The research, conducted by several universities including Princeton and Harvard, analyzed the type of atmospheres the seven TRAPPIST-1 planets could have, as well as their "implications for habitability."

"The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability," the authors write in their paper, published on December 28 in the journal Proceedings of the National Academy of Sciences.

The team devised an analytical model that simulates the stellar winds produced by TRAPPIST-1, and calculated how these winds affect each of the seven planets orbiting the red dwarf.

Stellar winds typically blast the planetary surface at speeds of up to 1,000 miles per second, notes Newsweek, and can deplete the atmosphere of a planet. This is especially problematic in the case of the TRAPPIST-1 exoplanets, which orbit their parent star closer than Mercury orbits the Sun. Their proximity to the red dwarf increases their chances of stellar winds deteriorating their atmospheres, shows Forbes, citing a study published on July 10 in The Astrophysical Journal Letters.

Nevertheless, the Princeton and Harvard simulations have shown that the outer planets TRAPPIST-1g and h have enough protection from the stellar winds to be able to support an atmosphere.

"We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales."
This puts TRAPPIST-1g in the cards as a possible home for alien life, considering this rocky exoplanet lies in the star's habitable zone and could have both liquid water and an atmosphere.

A digital illustration of the exoplanet TRAPPIST-1f.
This digital illustration shows the view from TRAPPIST-1f, one of the three exoplanets found in the red dwarf's habitable zone.

Furthermore, the study revealed that TRAPPIST-1b, the closest planet to the red dwarf and the most affected by its stellar winds, lies within the star's so-called critical surface, that could cause it to interact magnetically with TRAPPIST-1, Newsweek reports.

However, further research is required to confirm these calculations, the team clarifies.

"In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution," the authors caution in the abstract of their paper.