Although seven rocky planets orbit the red dwarf TRAPPIST-1, astronomers are particularly interested in TRAPPIST-1 e—a planet slightly smaller than Earth, located in a zone where liquid water could potentially exist. Recently, two independent research teams using the James Webb Space Telescope reported that a primordial atmosphere is almost certainly absent on this planet. However, the question of a secondary atmosphere remains open: it is quite possible that TRAPPIST-1 e has an atmosphere similar to Earth's.

Features of TRAPPIST-1 e

TRAPPIST-1 e is located about 40 light-years from Earth and completes a full orbit around its star in just 6.1 days. Due to tidal locking—where gravity causes the planet to always show the same face to its star—one hemisphere of this world is likely in constant daylight.

The planet lies within the habitable zone, and its equilibrium temperature (not accounting for the greenhouse effect) is estimated at –23°C (for comparison, Earth's is –18°C). Researchers believe that if an atmosphere is present, liquid water could exist on the illuminated side of TRAPPIST-1 e—either in localized areas or as a global ocean. Previously, astrobiologists using probabilistic mathematical models included TRAPPIST-1 e among the most promising exoplanets for the search for life.

Searching for an Atmosphere with the James Webb Telescope

To check for the presence of an atmosphere, astronomers observed TRAPPIST-1 e using the NIRSpec instrument aboard the James Webb Space Telescope. This device records how some of the star’s light passes through the planet’s atmosphere during transit. If an atmosphere exists, characteristic “dips” appear in the spectrum, corresponding to specific chemical substances. The more transits observed, the clearer the picture becomes.

Research Findings

Two scientific papers published in The Astrophysical Journal Letters showed that TRAPPIST-1 e almost certainly lacks a primordial hydrogen-helium envelope, and the presence of a dense carbon dioxide (CO₂) atmosphere is unlikely.

A team led by Nestor Espinoza from Johns Hopkins University analyzed the first transit spectra of TRAPPIST-1 e. However, the data were distorted by stellar activity—flares and spots on the star’s surface. To filter out this “noise,” the researchers used Gaussian process methods, allowing them to separate the star’s influence from possible atmospheric signals. As a result, they ruled out the possibility of a massive hydrogen envelope similar to the atmospheres of gas giants.

The second research group, led by Anna Glidden from the Massachusetts Institute of Technology, focused on modeling various scenarios for a secondary atmosphere—from its complete absence to the presence of a nitrogen-rich atmosphere with traces of methane and carbon dioxide.

Possible Scenarios

The existence of a nitrogen atmosphere or a completely airless surface is possible if a hydrogen gas envelope is ruled out (as confirmed by Espinoza’s team). Glidden and her colleagues did not find clear evidence of an atmosphere, but neither did they prove its complete absence.

Prospects for Further Research

Stellar activity complicates definitive conclusions about the presence of a secondary atmosphere on TRAPPIST-1 e, so scientists continue their observations with the James Webb Space Telescope. If this rocky planet does have an atmosphere, the likelihood of liquid water—and therefore conditions suitable for life—on its surface increases significantly.