JWST data suggest TRAPPIST-1e may host an Earth-like, nitrogen-rich atmosphere

Initial observations from the James Webb Space Telescope indicate that TRAPPIST-1e, a rocky planet in the nearby TRAPPIST-1 system, may possess an atmosphere with a composition similar to Earth's, according to two papers published Monday in the Astrophysical Journal Letters. The finding raises the possibility that liquid water could exist on the planet's surface and strengthens its status as a leading candidate in the search for habitable worlds beyond the solar system.

TRAPPIST-1e orbits an ultra-cool red dwarf about 40 light-years from Earth and is one of seven known planets in the system. The new analyses by teams of researchers — drawing on transit observations from Webb — suggest the planet lacks a cloud-free, hydrogen-dominated envelope and that a heavier, nitrogen-rich atmosphere is consistent with the data. Such an atmosphere would be more likely to allow temperate surface conditions, increasing the chance that liquid water, a key ingredient for life as we know it, could persist.

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"If there's one of these planets that could potentially sustain liquid water on the surface, it's probably that one," said Nikole Lewis, an exoplanet researcher at Cornell University and a co-author on the two papers, in an interview with the New York Times. Néstor Espinoza, an astrophysicist at the Space Telescope Science Institute in Baltimore and another author of both studies, told the newspaper that the presence of an atmosphere remains unconfirmed but that Webb's measurements place such an atmosphere "within the realm of possibility."

The teams used Webb to observe starlight filtering through TRAPPIST-1e's atmosphere during planetary transits, a technique known as transmission spectroscopy. The initial spectra do not match expectations for a puffy, hydrogen-rich atmosphere, which would produce clear molecular signatures in the infrared. Instead, the null detection of such signatures is more consistent with a compact, heavier atmosphere dominated by molecules such as nitrogen, or with high-altitude clouds or hazes that could mute observable features.

Ryan MacDonald, a co-author on both papers, said researchers plan to observe TRAPPIST-1e during 15 additional transits over the coming years to build a stronger dataset and attempt to confirm the atmospheric composition. Those follow-up measurements are intended to distinguish between a nitrogen-rich atmosphere, a high-cloud scenario, or other explanations for the current signals.

Both Earth and Saturn's moon Titan have atmospheres dominated by nitrogen; Titan is the only moon in the solar system known to host a substantial, multi-layered atmosphere with clouds and surface liquids. While the comparison underscores the significance of a nitrogen-rich envelope for habitability, the authors emphasized that JWST has not imaged TRAPPIST-1e's surface and that direct evidence of liquid water remains absent.

The TRAPPIST-1 system has for years been of exceptional interest to astronomers because multiple planets lie within or near the star's temperate zone. TRAPPIST-1e, situated in the system's so-called habitable zone, receives a level of stellar energy that could allow moderate surface temperatures if an appropriate atmosphere is present.

The new results arrive amid a wave of astrobiological developments. Separately, a study published this week in Nature reported that NASA's Perseverance rover found distinctive spotted rocks in Neretva Vallis on Mars that scientists described as potential biosignatures or indicators of past habitable conditions. Together, the findings on Mars and TRAPPIST-1e underscore growing capabilities to probe environments both within and beyond the solar system for conditions conducive to life.

The authors of the TRAPPIST-1e papers caution that interpretation of transmission spectra is complex and that additional Webb observations will be critical to test competing models. If confirmed, a nitrogen-rich atmosphere on a rocky planet so close to Earth in astronomical terms would mark a major step in the study of planetary habitability and guide future observational strategies for characterizing exoplanetary surfaces and climates.

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The papers are among the first wave of peer-reviewed results from Webb's targeted campaign on the TRAPPIST-1 system, and teams worldwide are analyzing additional data as the telescope continues a multi-year program to observe the seven planets during repeated transits. Researchers said the next set of observations will be decisive in determining whether TRAPPIST-1e's atmosphere is truly Earth-like in composition and capable of supporting stable surface liquid water.