🪐 Hope for extraterrestrial life on TRAPPIST-1e, despite its star's fury

A red dwarf star, TRAPPIST-1, close to us at 40 light-years, produces powerful flares several times a day. And yet, it hosts seven Earth-sized planets, three of which are located in the zone where water could be liquid. Could these worlds harbor life in such a turbulent environment?

Recent observations from the James Webb Space Telescope have tracked six of these flares in 2022 and 2023. Thanks to its infrared sensors, the instrument has detected large luminous flashes that betray the heat released by the star during each event. By combining this data with computer simulations, a research team has reconstructed the physical processes behind these stellar outbursts. This approach has made it possible to estimate the properties of the electron beams that trigger them.


A surprising result is that the electron beams responsible for these flares appear to be about ten times less intense than those observed in similar stars. However, this does not make them harmless. Each flare emits radiation covering the entire spectrum, from visible light to ultraviolet and powerful X-rays. Over time, this radiation can erode or profoundly alter planetary atmospheres.

Thus, using their models, the researchers were able to reverse the reasoning to understand how a flare influences the radiative environment around each planet. According to lead study author Ward Howard, cited in a University of Colorado Boulder press release, this method helps determine which worlds might retain an atmosphere conducive to life.

Consequently, the planets closest to TRAPPIST-1 have likely lost their atmosphere, leaving bare rocks. In contrast, a planet located in the habitable zone, named TRAPPIST-1e, might still possess an atmosphere similar to Earth's. This possibility suggests conditions that could be favorable for life, despite the intense stellar activity typical of red dwarfs (see below).

The work published on November 20 in *Astrophysical Journal Letters* thus shows that studying the flare behavior of TRAPPIST-1 allows for refining predictions about the survival of planetary atmospheres. Rather than mere disturbances or destructive forces, these phenomena become valuable tools for guiding the search for life beyond our Solar System.

Red dwarfs and their stellar activity

Red dwarfs like TRAPPIST-1 represent the most common type of star in our Galaxy. They are much smaller and cooler than our Sun, and they can live for tens of billions of years, thus offering an extended timeframe for the development of life. Their low luminosity means their habitable zones are located very close to the star, where planets are more exposed to stellar radiation.

This increased proximity makes planets orbiting red dwarfs particularly vulnerable to stellar flares. These events release large amounts of energy in the form of ultraviolet radiation and X-rays, which can bombard planetary atmospheres. Over long periods, this bombardment can lead to the evaporation of atmospheric gases, especially if the planet lacks a sufficiently protective magnetic field.

Understanding the activity of red dwarfs is therefore essential for assessing the habitability of their exoplanets. Researchers use telescopes like James Webb to monitor these stars and model their impacts. This allows for creating scenarios about how atmospheres evolve under the effect of flares, helping to identify the most promising worlds for future studies.

This approach opens new perspectives in the search for extraterrestrial life, as it allows targeting systems where conditions might remain stable despite the turbulent environment. By studying TRAPPIST-1, scientists hope to establish more precise criteria for distinguishing habitable planets from others in our galactic neighborhood.