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When the JWST finally began its long-awaited science operations in July 2022, there was a long list of targets awaiting its attention. Scientists compete for observing time by submitting proposals, and for every nine submitted proposals, only one gets approved. In the most recent Cycle 4 of the telescope's mission, scientists requested about 78,000 hours of observing time when only about 8700 were available.

To deal with this, proposals are rigorously scrutinized for their value. The JWST has four main science themes, and one of them is "Planetary Systems and the Origins of Life." The TRAPPIST-1 system is a perfect fit for observations under this theme, and astronomers eagerly awaited the JWST's launch, knowing that it would eventually turn its infrared eye on the system and its seven Earth-sized, rocky planets.

The JWST has already observed TRAPPIST-1 b, c, and d. Its newest target is TRAPPIST-1 e (T1e). T1e is in the habitable zone of the star, and was considered the most likely planet to retain surface water under a wide variety of potential conditions. The results of the telescope's observations are in a pair of papers published in The Astrophysical Journal Letters. The observations are ongoing, and are based on the first four transits the telescope observed.

"TRAPPIST-1 e is one of the very few rocky exoplanets that is both amenable to atmospheric characterization and resides in the habitable zone of its star—located at a distance from its star such that it might, with the right atmosphere, sustain liquid water on its surface," states the first paper.

The JWST observes exoplanet atmospheres spectroscopically in the infrared. Its wavelength coverage allows it to detect critical atmospheric constituents like water vapor, carbon dioxide, methane, and ammonia. These molecules are key indicators for atmospheres, and play a big role in understanding how atmospheres form, evolve, and become potentially life-supporting. The JWST's large 6.5 meter mirror and its sensitive instruments let the telescope detect even small spectroscopic signals from these molecules and others.

"Webb's infrared instruments are giving us more detail than we've ever had access to before, and the initial four observations we've been able to make of planet e are showing us what we will have to work with when the rest of the information comes in," said Néstor Espinoza of the Space Telescope Science Institute. Espinoza is the lead author of one of the new papers.

The first four transits indicate that T1e has lost its primary atmosphere due to stellar flaring from the red dwarf star it orbits. But these observations also present several different scenarios for the planet. For instance, they can't eliminate the possibility of an atmosphere since some of the data suggests the planet does have one. Planets can acquire secondary atmospheres after their primary is stripped away. That's what happened on Earth.

The above graphic does a good job of presenting the JWST's spectroscopic results from four transits of T1e in front of its star. In reality, the data is nowhere near as clear and has to be analyzed in depth to extract meaning.

The differences in the four spectra above are probably related to stellar flaring. As a red dwarf, TRAPPIST-1 is known for powerful flaring that likely stripped the primordial hydrogen/helium atmospheres from the planets. The same flaring contaminates the JWST's spectra.

"Our transmission spectra exhibit similar levels of stellar contamination as observed in prior works for other planets in the TRAPPIST-1 system but over a wider wavelength range, showcasing the challenge of characterizing the TRAPPIST-1 planets even at relatively long wavelengths," the authors of the first paper explain.

The exoplanet's atmosphere is unlikely to be dominated by carbon dioxide like Venus's thick atmosphere and Mars's thin one. In fact, it doesn't appear similar to any body in our solar system. That's not surprising, since the star itself is vastly different from our stable, main sequence star.

"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 first study co-author Nikole Lewis, an associate professor of astronomy at Cornell University.

However, the lack of detected carbon dioxide may prevent the planet from experiencing the greenhouse effect. According to the researchers, the greenhouse effect may be necessary for the T1e to maintain surface water. But interpreting the JWST data is complex and observations are incomplete. The observations can't rule out some carbon dioxide, and there may be enough to preserve some amount of surface water.

"A little greenhouse effect goes a long way," said Lewis in a .

In the second paper, modeling of the JWST spectra suggests the presence of methane (CH4). Thick, methane dominated atmospheres are ruled out, but lower abundances of CH4 with higher N2 partial pressures can't be ruled out.

"If an atmosphere exists on TRAPPIST-1 e, our data suggest that it is best matched by a relatively heavy, spectrally inactive gas together with CH4," write Glidden and her co-authors in the second paper. "However, we stress that the evidence neither warrants the detection of an atmosphere nor rules one out."

Fortunately, there are 15 upcoming observations of T1e that will feature a new innovation. Espinoza, the lead author of the first paper, and co-investigator Natalie Allen of Johns Hopkins University, have developed a way to get a clearer picture of T1e's atmosphere with the JWST. It involves another of the TRAPPIST-1 planets, T1-b.

T1-b is the closest planet to its star, and the JWST has already observed it. Astronomers are confident it's just bare rock with no atmosphere. It's so close to the star that stellar stripping is a near certainty. Since T1-b transits the star right before T1-e does, astronomers can compare the spectra from each one at nearly the same time.

Any stellar artifacts present at the time of observations can be quantified by the way they appear in the spectra from T1-b then removed from the observations of T1-e. So any chemical indicators present in T1-e's spectra can be confirmed as part of its atmosphere.

"We are really still in the early stages of learning what kind of amazing science we can do with Webb," said Ana Glidden. Glidden is a post-doctoral researcher at MIT's Kavli Institute, and the lead author of the second paper. "It's incredible to measure the details of starlight around Earth-sized planets 40 light-years away and learn what it might be like there, if life could be possible there. We're in a new age of exploration that's very exciting to be a part of," she said.

While the four JWST observations so far can't conclude exactly what T1e's atmosphere is like, they constrain the possibilities. Just as planned and expected, the powerful telescope is heralding a new era in this age of exoplanets. We've moved from merely discovering them to studying their atmospheres in detail.

"We show that with the current data set, we are unable to distinguish between an atmosphere and atmosphereless scenario for TRAPPIST-1 e," Espinoza et al. write in their paper, while also acknowledging that they've made progress by constraining the possibilities. "Our work does highlight, however, how JWST is breaking ground in the study of rocky HZ exoplanet atmospheric compositions."