Peering Into TRAPPIST-1e: JWST’s First Glimpses of a Habitable-Zone Rocky World

TRAPPIST-1e is one of seven Earth-sized planets orbiting the small, cool star TRAPPIST-1. What makes it special is that it lies in the star’s “habitable zone,” the distance where liquid water might exist if the right atmosphere is present. In this study, Espinoza and collaborators used NASA’s James Webb Space Telescope (JWST) to take four detailed looks at the planet in 2023, hoping to learn what its atmosphere is like.

Why TRAPPIST-1 Matters

The TRAPPIST-1 system is especially promising for atmospheric studies. Because the star is so small, planets passing in front of it block a relatively large fraction of its light, making their signals easier to detect. However, the system’s star is also very active, producing frequent flares and spots on its surface. These stellar features complicate the view, creating “contamination” that mimics or hides the planet’s atmospheric signals.

Observing the Transits

Espinoza’s team observed four transits of TRAPPIST-1e, moments when the planet passed in front of its star, using JWST’s NIRSpec instrument. These observations captured starlight filtered through the planet’s potential atmosphere, covering wavelengths from 0.6 to 5 micrometers. Even though the data were precise, they revealed strong variability between different observing dates, likely caused by the changing surface of the star rather than the planet itself.

Dealing With Stellar Contamination

Existing computer models of stars could not fully explain the strange patterns seen in the data. To tackle this, the researchers developed a new method using Gaussian processes, a statistical approach that helps account for unknown or poorly modeled effects. This allowed them to “marginalize over” (essentially, remove the influence of) stellar contamination and focus on signals that might come from TRAPPIST-1e’s atmosphere.

What They Found

After correcting the data, the team reached remarkable precision, able to detect atmospheric features as small as 50 parts per million. However, they could not clearly distinguish whether TRAPPIST-1e has an atmosphere. What they could do is rule out one major possibility: the planet almost certainly does not have a thick, hydrogen-dominated atmosphere like Jupiter’s. Such an atmosphere would have been obvious in the data, but it wasn’t there. Instead, if TRAPPIST-1e has an atmosphere at all, it is more likely to be a “secondary atmosphere” rich in heavier gases like carbon dioxide, similar to Venus, Earth, or Mars.

Why This Matters

This study marks one of the most precise attempts yet to probe the atmosphere of a rocky planet in the habitable zone. While the results don’t give a final answer on whether TRAPPIST-1e has an atmosphere, they demonstrate both the power and the difficulty of using JWST for such work. The star’s own activity remains the biggest obstacle, but with new techniques and future data sets, including many more transits of TRAPPIST-1e and its siblings, astronomers are steadily moving closer to answering whether worlds like this could truly be habitable.

Source: Espinoza