Which TRAPPIST-1 Planet Might Be Habitable? JWST Flares Reveal New Clues

Frequent eruptions from the nearby ultracool red dwarf TRAPPIST-1 are giving astronomers fresh clues about which of its worlds could keep an atmosphere and possibly support life. Located about 40 light-years away in the constellation Aquarius, TRAPPIST-1 hosts seven Earth-size planets, three of which orbit in the system's habitable zone where liquid water could exist.

JWST Observations and Modeling

Using infrared data from the James Webb Space Telescope (JWST), researchers analyzed six flares observed in 2022 and 2023. On JWST's detectors each flare appears as a sharp, bright flash that reveals how much heat and energy the star releases during an outburst. The team combined those measurements with detailed computer simulations to reconstruct the physical processes behind each event and estimate the properties of the electron beams that seem to trigger the flares.

"If we can simulate these events using a computer model, we can reverse engineer how a flare might influence the radiation environment around each of these planets," said Ward Howard, the study's lead author.

What the Flares Mean for Habitability

Surprisingly, the inferred electron beams are about ten times weaker than those measured on comparable active stars. That reduced beam strength, however, does not make the flares harmless: each outburst emits energy across the spectrum—from visible light through ultraviolet and into energetic X-rays—which can gradually erode or chemically alter planetary atmospheres.

Based on their modeling, the researchers suggest the system's innermost planets may already have lost their atmospheres and could now be barren rock. By contrast, TRAPPIST-1e, a planet in the habitable zone, remains a promising candidate that could plausibly retain a thin, Earth-like atmosphere, making it one of the best targets in the system for further searches for habitable conditions.

Rather than being mere nuisances for observers, the star's flares can be read as diagnostic signals that reveal how harsh the radiation environment is around each planet. Decoding that behavior helps scientists refine which worlds are most likely to preserve atmospheres and, ultimately, which merit deeper study for signs of habitability.

Study published Nov. 20 in the Astrophysical Journal Letters. Analysis led by researchers at the University of Colorado Boulder using JWST data from 2022–2023.