Astronomers led by a team from the University of Montreal have made significant progress in understanding the fascinating exoplanet system TRAPPIST-1, first discovered in 2016 when it was thought it may one day provide habitat for humans. New research not only sheds light on the nature of TRAPPIST-1 b, the exoplanet orbiting the star of the unified system, but also shows the importance of parent stars in the study of exoplanets. Published in the Astrophysical Journal, the findings by astronomers from the Trottier Institute for Exoplanet Research (iREx) at UdeM and colleagues from Canada, the UK and the US have sheds light on the complex interactions between stellar activity and the characteristics of exoplanets.
TRAPPIST-1, a star much smaller and cooler than our sun located about 40 light-years from Earth, has attracted the attention of scientists and space enthusiasts since upon the discovery of seven exoplanets the size of Earth seven years ago. These worlds, tightly clustered around their star, including three worlds in the habitable zone, have raised hopes of finding habitable environments beyond our solar system . Led by iREx doctoral student Olivia Lim, the researchers used the powerful James Webb Space Telescope (JWST) to observe TRAPPIST-1 b. Their observations were collected as part of the largest Canadian-led General Observer (GO) program during JWST’s first year of operations. (This program also includes observations of three other planets in the system, TRAPPIST-1 c, g, and h.) TRAPPIST-1 b was observed during two transits—when the planet passed ahead Its star — using the Canadian system — produces the NIRISS device aboard the JWST. “These are the first spectroscopic observations of the planet TRAPPIST-1 that JWST has obtained, and we have been waiting for them for many years,” said Lim, GO principal investigator.
She and her colleagues used transmission spectroscopy techniques to look deeper into distant worlds. By analyzing the light from the central star after it passes through the exoplanet’s atmosphere during transit, astronomers can see unique fingerprints left by molecules and atoms looking for seen in the atmosphere that left behind.
“This is just a small set of many other observations of this unique planetary system,” added René Doyon, principal investigator of the NIRISS instrument and co-author of the study. “These initial observations highlight the power of NIRISS and JWST in general in probing thin atmospheres around rocky planets.” The astronomers’ main discovery was the importance of stellar activity and contamination when trying to determine the nature of an exoplanet. Stellar contamination refers to the influence of a star’s unique features, such as dark spots and bright surfaces, on measurements of an exoplanet’s atmosphere.
The team found compelling evidence that stellar contamination plays an important role in shaping the transmission spectra of TRAPPIST-1 b and possibly other planets in the system. The central star’s activity can produce a “ghost signal” that could fool observers into thinking they have detected a specific molecule in the exoplanet’s atmosphere. The results highlight the importance of taking stellar contamination into account when planning future observations of all exoplanetary systems, the scientists said. This is especially true of systems like TRAPPIST-1, since the system is centered around a red dwarf star that can be exceptionally active with frequent starspots and halos. “In addition to contamination by star spots and streaks, we also observed stellar flares, an unpredictable event in which a star appears brighter for a few minutes or hours,” Lim said. . “This eruption affected our measurements of the amount of light blocked by the planet. Such signatures of stellar activity are difficult to model, but we must take them into account to ensure accurate interpretation of the data.
Based on the observations JWST collected, Lim and his team explored a series of atmospheric models for TRAPPIST-1 b, considering different components and possible scenarios. They found that they could confidently rule out the existence of a cloudless, hydrogen-rich atmosphere – in other words, there appeared to be no widespread, transparent atmosphere around TRAPPIST-1 b. However, the data cannot confidently rule out thinner atmospheres, such as those consisting of pure water, carbon dioxide or methane, as well as atmospheres similar to Titan’s moon. Earth and the only moon of the solar system with its own atmosphere.