Free Astronomy Magazine November-December 2025

29 NOVEMBER-DECEMBER 2025 TRAPPIST-1 d, the third planet from the red dwarf star, lies on the cusp of that temperate zone, yet its dis- tance to its star is only 2 percent of Earth’s distance from the Sun. TRAP- PIST-1 d completes an entire orbit around its star, its year, in only four Earth days. Webb’s NIRSpec (Near-In- frared Spectrograph) instrument did not detect molecules from TRAPPIST- 1 d that are common in Earth’s at- mosphere, like water, methane, or carbon dioxide. However, Piaulet- Ghorayeb outlined several possibili- ties for the exoplanet that remain open for follow- up study. “There are a few poten- tial reasons why we don’t detect an atmosphere around TRAPPIST- 1 d. It could have an extremely thin atmosphere that is difficult to de- tect, somewhat like Mars. Alter- natively, it could have very thick, h i g h - a l t i t u d e clouds that are blocking our de- tection of specific atmospheric sig- natures — some- thing more like Venus. Or, it could be a barren rock, with no atmos- phere at all,” Pi- aulet-Ghorayeb said. No matter what the case may be for TRAP- PIST-1 d, it’s tough being a planet in orbit around a red dwarf star. TRAP- PIST-1, the host star of the sys- tem, is known to be volatile, often releasing flares of high-energy radi- ation with the potential to strip off the atmospheres of its small plan- ets, especially those orbiting most closely. Nevertheless, scientists are motivated to seek signs of atmos- pheres on the TRAPPIST-1 planets because red dwarf stars are the most common stars in our galaxy. If plan- ets can hold on to an atmosphere here, under waves of harsh stellar radiation, they could, as the saying goes, make it anywhere. “Webb’s sensitive infrared instruments are al- lowing us to delve into the atmos- pheres of these smaller, colder plan- ets for the first time,” said Björn Benneke of IREx at Université de Montréal, a co-author of the study. “We’re really just getting started using Webb to look for atmospheres on Earth-sized planets, and to define the line between planets that can hold onto an atmosphere, and those that cannot.” Webb observations of the outer TRAPPIST-1 planets are on- going, which hold both potential and peril. On the one hand, Benneke said, planets e, f, g, and h may have better chances of having atmos- pheres because they are further away from the energetic eruptions of their host star. However, their dis- tance and colder environment will make atmospheric signatures more difficult to detect, even with Webb’s infrared instruments. “All hope is not lost for atmospheres around the TRAPPIST-1 planets,” Piaulet-Gho- rayeb said. “While we didn’t find a big, bold atmospheric signature at planet d, there is still potential for the outer planets to be holding onto a lot of water and other atmospheric components.” “As NASA leads the way in searching for life outside our solar system, one of the most important avenues we can pursue is understanding which planets retain their atmospheres, and why,” said Shawn Domagal-Gold- man, acting director of the Astro- physics Division at NASA Head- quarters in Washington. “NASA’s James Webb Space Telescope has pushed our capabilities for studying exoplanet atmospheres further than ever before, beyond extreme worlds to some rocky planets – allowing us to begin confirming theories about the kind of planets that may be po- tentially habitable. This important groundwork will position our next missions, like NASA’s Habitable Worlds Observatory, to answer a uni- versal question: Are we alone?” ! T his artist’s concept depicts planet TRAPPIST-1 d passing in front of its turbulent star, with other mem- bers of the closely packed system shown in the background. [NASA, ESA, CSA, Joseph Olmsted (STScI)]