Ann Arbor Times

University of Michigan researchers, as part of an international team, have reported that a rocky planet located 40 light-years away in the TRAPPIST-1 system may possess an atmosphere. This finding could indicate the potential for conditions suitable for life.

The studies, published in the Astrophysical Journal Letters, focus on TRAPPIST-1 e, an Earth-sized exoplanet situated within its star’s habitable zone. The presence of liquid water on this planet would depend on whether it has an atmosphere. Despite some uncertainty remaining about the exact nature of TRAPPIST-1 e, researchers believe they are closer to determining its atmospheric composition.

“We are seeing two possible explanations. The most exciting possibility is that TRAPPIST-1 e could have a so-called secondary atmosphere containing heavy gases like nitrogen. But our initial observations cannot yet rule out a bare rock with no atmosphere,” said Ryan MacDonald, who contributed to the studies as a NASA Sagan Fellow in the U-M Department of Astronomy and is now at the University of St. Andrews.

The research utilized data from the James Webb Space Telescope (JWST), which is operated by NASA with support from both the European Space Agency and Canadian Space Agency. The two papers were led by Néstor Espinoza from the Space Telescope Science Institute and Ana Glidden from MIT’s Kavli Institute for Astrophysics and Space Research. More than 30 scientists from multiple countries participated in these efforts.

“In the coming years we will go from four JWST observations of TRAPPIST-1 e to nearly twenty,” MacDonald said. “We finally have the telescope and tools to search for habitable conditions in other star systems, which makes today one of the most exciting times for astronomy.”

TRAPPIST-1 e draws particular interest among seven Earth-sized planets orbiting its red dwarf star because it lies at a distance where surface water could exist—if there is an atmosphere present.

“TRAPPIST-1 e has long been considered one of the best habitable zone planets to search for an atmosphere,” MacDonald said. “But when our observations came down in 2023, we quickly realized that the system’s red dwarf star was contaminating our data in ways that made the search for an atmosphere extremely challenging.”

Researchers used JWST’s Near-Infrared Spectrograph (NIRSpec) instrument during planetary transits to gather data about any potential atmospheric chemicals through changes observed in starlight passing through or around TRAPPIST-1 e.

“When JWST was being designed, we only knew of a handful of planets around a few stars. Over time, it became clear that JWST would be a powerful tool to help figure out their composition,” said Michael Meyer, professor and chair of U-M’s Department of Astronomy. Although not directly involved with these studies, Meyer contributed over two decades developing relevant instrumentation and science programs.

With only four transits analyzed so far, several scenarios remain possible regarding TRAPPIST-1 e's environment; however, scientists are confident that any original hydrogen-helium primary atmosphere has likely been stripped away due to frequent stellar flares from its active host star.

Planets can develop secondary atmospheres composed mainly of heavier elements after losing their primary ones—a process seen on Earth as well as other bodies within our solar system. According to current findings, there are roughly equal chances that TRAPPIST-1 e either possesses such a secondary atmosphere or remains without one.

If a secondary atmosphere exists along with liquid water on this exoplanet, researchers expect greenhouse gases like carbon dioxide would play a key role in maintaining stable temperatures—a process different from what occurs on Mars or Venus despite similar chemical components.

“TRAPPIST-1 is a very different star from our sun, and so the planetary system around it is also very different, which challenges both our observational and theoretical assumptions,” said Nikole Lewis, associate professor at Cornell University and subject lead for exoplanet transit spectroscopy on JWST's scientist team. She added: “a little greenhouse effect goes a long way.”

Current measurements do not exclude enough carbon dioxide being present to sustain some surface water—potentially forming either global oceans or localized areas surrounded by ice depending on planetary conditions.