A series of occurrences in the evolutionary process of specific rocky planets orbiting M-dwarfs, the most prevalent type of stars in the universe, results in the development of a stable atmosphere. This particularly applies to temperate planets located at a greater distance from their central star.
Since its launch in late 2021, NASA’s James Webb Space Telescope has opened up the possibility of detecting signs of life on exoplanets—planets situated beyond our solar system.
Prominent candidates in this investigation are rocky planets, as opposed to gaseous ones, which orbit low-mass stars known as M-dwarfs—by far the most common stars across the universe. A notable nearby M-dwarf is TRAPPIST-1, a star located approximately 40 light years away, which contains a system of orbiting planets that is currently being closely examined in the quest for life beyond our sun.
Earlier studies raised doubts about the habitability of planets around TRAPPIST-1, highlighting that intense UV radiation could evaporate their surface water. This would lead to a dry planet with potentially large quantities of reactive oxygen created if only hydrogen from water vapor escaped, which could hinder the chemistry required for life’s origin.
Recently, a study led by the University of Washington and published in Nature Communications reveals that a specific sequence of events during the evolution of certain rocky planets orbiting M-dwarfs allows for the formation of a stable atmosphere over time.
“One of the most captivating questions in current exoplanet astronomy is whether rocky planets orbiting M-dwarfs can sustain atmospheres capable of supporting life,” said Joshua Krissansen-Totton, the study’s lead author and a UW assistant professor of Earth and space sciences. “Our findings give us reason to believe that some of these planets indeed have atmospheres, which greatly improves the likelihood that these widespread planetary systems might harbor life.”
The James Webb Space Telescope is highly sensitive and can observe a few selected planetary systems. So far, the data indicates that the hottest rocky planets, located nearest to the TRAPPIST-1 star, lack significant atmospheres. However, the telescope hasn’t yet been able to effectively analyze planets lying in the “Goldilocks zone,” those slightly further from the star that are best positioned to support liquid water and life.
The new research simulated the evolution of a rocky planet from its molten state to its solid form over hundreds of millions of years. The results showed that while light gases like hydrogen initially escaped into space, planets at a greater distance from the star, where temperatures are cooler, saw hydrogen interact with oxygen and iron inside the planet. This reaction formed water and other heavier gases, creating a stable atmosphere over time.
Findings also indicated that for these planets in the “Goldilocks zone,” water falls out of the atmosphere relatively fast, reducing the chances of it escaping into space.
“It’s simpler for the JWST to observe hotter planets closer to the star because they radiate more thermal energy, which is less affected by stellar interference. For those planets, the answer is quite clear: they do not possess thick atmospheres,” Krissansen-Totton explained. “This result is particularly intriguing because it suggests that the more temperate planets may indeed have atmospheres and should be examined closely with telescopes, especially considering their potential for habitability.”
The JWST has yet to determine if the planets further from the TRAPPIST-1 star have atmospheres. If they do, it implies the potential presence of liquid water on their surfaces and a climate suitable for life.
“With the current telescopes, including the James Webb and the soon-to-be operational large ground-based telescopes, we can only analyze a limited number of atmospheres from rocky planets in the habitable zone—specifically the TRAPPIST-1 planets and a couple of others,” Krissansen-Totton noted. “Considering the extensive interest in the search for extraterrestrial life, our findings suggest that it’s valuable to dedicate telescope time to continue exploring the habitability of these systems using existing technology, rather than waiting for future, more advanced telescopes.”
Co-authors of this research include Nicholas Wogan, who conducted this study while a graduate student at UW and is now with NASA; Maggie Thompson from the Carnegie Institution for Science in Washington, D.C.; and Jonathan Fortney from the University of California, Santa Cruz. This research received support from NASA.
