The initial sniff of extraterrestrial air might already be within our telescopes’ reach. NASA’s James Webb Space Telescope (JWST) has yielded intriguing data indicating that TRAPPIST‑1e, a terrestrial planet around a diminutive red dwarf star only 41 light‑years from us, might be shrouded in a secondary atmosphere dense with heavy molecules like nitrogen or methane. If verified, it would be the first time that an atmosphere on a rocky exoplanet in the habitable zone of another star has been detected.
TRAPPIST‑1e finds itself within what astronomers refer to as the “Goldilocks zone,” the orbital range where stellar radiation is neither too strong nor too weak to support liquid water on a planet’s surface. But proximity alone is not sufficient. Without an atmosphere to retain heat by the greenhouse effect, any body of water would freeze or evaporate off into space. Greenhouse gases such as carbon dioxide, methane, and water vapor trap and re-emit infrared radiation, stabilizing climate and allowing oceans or lakes to be present. As Nikole Lewis of Cornell University said, “A little greenhouse effect goes a long way.”
The JWST crew pointed TRAPPIST‑1e with its Near-Infrared Spectrograph (NIRSpec) to conduct transmission spectroscopy taking a reading of the star’s light as it passes through the planet’s atmosphere as it transits. Molecules absorb particular wavelengths, so they leave unique “fingerprints” in the spectrum. Four such transits, seen between June and October 2023, already discounted a light, hydrogen‑rich primary atmosphere, which the planet probably lost long ago due to the harsh radiation and flares of its active red dwarf parent. Only a heavier, secondary atmosphere comparable in mass to that of Earth, or Saturn’s moon Titan’s nitrogen‑methane cloak is still possible.
Red dwarfs hold a special benefit for this type of work. Their compact size has the effect that a transiting planet eclipses a greater proportion of starlight, heightening the atmospheric signal. Their habitable zones are closer in as well, so planets orbit in days instead of years, which enables astronomers to observe many more transits in a short period of time. TRAPPIST‑1e, for instance, orbits its star every six days, which allows for repeated, high-cadence observations.
But the same stellar activity that erodes atmospheres also makes them harder to detect. TRAPPIST-1’s surface is speckled with warm faculae and cool starspots, areas that can fake or conceal atmospheric absorption features. This “stellar contamination” laid out in detail by NASA’s Study Analysis Group 21 can change inferred molecular abundances by as much as six orders of magnitude and bias temperature estimates by over 100 percent. To untangle the planet’s spectrum from the variability of the star, the JWST team is comparing consecutive TRAPPIST‑1b observations, a known bare rock, with TRAPPIST‑1e observations. Any spectral features that are only visible when TRAPPIST‑1e is in transit can be assigned to its atmosphere.
The current dataset is not yet able to tell the difference between a barren surface and an atmosphere that can support water. But the next stage is already in progress: fifteen further transits, set to complete by the end of 2025, will search for greenhouse gases such as methane and carbon dioxide. These are not just climate controllers but, in some mixtures, potential biosignatures. On Earth, the presence of both oxygen and methane is a powerful sign of life, although scientists warn that abiotic chemistry can create the same signature.
Infrared spectroscopy, JWST’s forte, is especially well-suited to finding such molecules. By covering wavelengths from red visible light to 5 microns, the telescope can detect absorption bands beyond the reach of previous observatories. The capability has already identified carbon dioxide and sulfur dioxide in exoplanet atmospheres as well as mapped temperature differences on faraway planets. For TRAPPIST-1e, the same level of accuracy would determine if its climate is moderated by a dense, stable atmosphere or exposed to the emptiness of space.
The consequences go far beyond one planet. As Néstor Espinoza of the Space Telescope Science Institute said, “It would settle a huge debate going on right now on whether these red dwarf systems can sustain an atmosphere or not. Red dwarfs are actually the majority of the stars in the universe. So, if it can happen there, it can happen anywhere.” A confirmed atmosphere on TRAPPIST‑1e would not just add to the list of possible habitable worlds but also tailor the engineering needed for upcoming telescopes to look for life.
For the time being, TRAPPIST-1e is at a scientific crossroads a planet that might be a frozen wasteland, a warm ocean world, or something in between. JWST’s ongoing vigil may soon tell us which face it presents to the galaxy.
