TRAPPIST-1 outer planets likely have water, research suggests

The TRAPPIST-1 solar system generated a swell of interest when it was observed several years ago. In 2016, astronomers using the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at La Silla Observatory in Chile ...

It was a remarkable discovery, especially because up to four of them could be the right distance from the star to have liquid water . The TRAPPIST-1 system still gets a lot of scientific attention. Potential Earth-like planets in a star's habitable zone are like magnets for planetary scientists. Finding seven of them in one system is a unique scientific opportunity to examine all kinds of interlinked questions about exoplanet habitability. TRAPPIST-1 is a red dwarf, and one of the most prominent questions about exoplanet habitability concerns red dwarfs (M dwarfs.) Do these stars and their powerful flares drive the atmospheres away from their planets?

New research accepted for publication in the Planetary Science Journal and available on the preprint server arXiv , examines atmospheric escape on the TRAPPIST-1 planets. Its title is "The Implications of Thermal Hydrodynamic Atmospheric Escape on the TRAPPIST-1 Planets." Megan Gialluca, a graduate student in the Department of Astronomy and Astrobiology Program at the University of Washington, is the lead author. Most stars in the Milky Way are M dwarfs. As the TRAPPIST-1 makes clear, they can host many terrestrial planets . Large, Jupiter-size planets are comparatively rare around these types of stars.

Three of the TRAPPIST-1 planets—TRAPPIST-1e, f and g—dwell in their star's so-called "habitable zone." Credit: NASA/JPL Read more

Artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. Credit: NASA/JPL Read more

In this research, the authors took into account the predicted present-day water content for each of the outer planets and then worked backwards to understand their initial water content. This figure shows "The likelihood of each initial water content (in TO) needed to reproduce the predicted present-day water contents for each of the outer planets," the authors write. The four outer planets would've started out with enormous amounts of water compared to Earth. Credit: Gialluca et al, 2024 Read more