JWST just scanned the skies of potentially habitable exoplanet TRAPPIST-1 b

About 40 light years away, there is a system known as TRAPPIST-1, which contains seven Earth-sized planets orbiting a star much cooler and smaller than our Sun. Discovered in 2016, these planets have sparked interest due to their potential to support conditions that might be suitable for life. Three of these planets are located in the star’s habitable zone, often referred to as the “Goldilocks zone,” where conditions could potentially allow for liquid water.

Recent observations using the James Webb Space Telescope (JWST) have advanced our understanding of one of these planets. Specifically, the JWST has studied TRAPPIST-1 b, the planet closest to its star. The telescope’s observations have ruled out the presence of a thick, extended atmosphere, and have not detected elements such as hydrogen. The study also managed to mitigate interference from the star, improving the clarity of the data. These findings are detailed in a study published on September 22 in The Astrophysical Journal Letters.

The research involved using the JWST’s NIRISS instrument to observe TRAPPIST-1 b during two transits, when the planet crossed in front of its star. This allowed the team from institutions in the United States and Canada to gather valuable data about the planet’s atmospheric properties.

The team employed a technique known as transmission spectroscopy to analyze the atmosphere of TRAPPIST-1 b. This method allowed them to detect the unique spectral signatures of molecules and atoms within the planet’s atmosphere. “These are the first spectroscopic observations of any TRAPPIST-1 planet obtained by the JWST, and we’ve been anticipating them for years,” said Olivia Lim, a doctoral student at Université de Montréal and co-author of the study.

Previous observations of exoplanets have sometimes been complicated by the influence of their host stars. These stars can produce “ghost signals” that mislead researchers into detecting false molecular signatures in the exoplanet’s atmosphere. This issue, known as stellar contamination, arises from the star’s own features—such as sunspots and bright faculae—distorting the chemical fingerprints detected by telescopes.

Additionally, the team encountered a stellar flare during their observations, an unpredictable event that caused the star to appear temporarily brighter. “This flare affected our measurements of the light blocked by the planet,” Lim explained. “Such stellar activity can be challenging to model, but it’s crucial to account for it to interpret the data accurately.”

Using their observations, the team tested various atmospheric models for TRAPPIST-1 b and ruled out the possibility of a cloud-free, hydrogen-rich atmosphere. This suggests that the planet is unlikely to have a thick, extended atmosphere. However, the data did not conclusively rule out the presence of a thinner atmosphere that could consist of substances like water vapor, carbon dioxide, or methane.

According to the team, these results highlight the need to account for stellar contamination when planning future observations of exoplanetary systems. This is particularly important for systems like TRAPPIST-1, which is centered around a red dwarf star known for its frequent flares and sunspots.

Further observations are required to better understand the composition of TRAPPIST-1 b’s atmosphere and to assess its potential for supporting human life. “These initial observations are just the beginning,” said René Doyon, a study co-author and astronomer at Université de Montréal. “They demonstrate the capabilities of the NIRISS instrument and the James Webb Space Telescope in studying the atmospheres of rocky planets, but many more observations and analyses will be needed to gain a clearer picture.”