A groundbreaking international collaboration, including researchers from the University of Bern (UNIBE) and the University of Geneva (UNIGE), has achieved an unprecedented milestone in exoplanetary science. For the first time, scientists have successfully mapped the climate of Earth-sized rocky exoplanets, unveiling new insights into the atmospheres—or alarming lack thereof—of worlds orbiting a distant star. This landmark achievement was made possible through continuous observations with the James Webb Space Telescope (JWST), focusing intently on the two innermost planets of the iconic TRAPPIST-1 system, known as TRAPPIST-1b and TRAPPIST-1c. These findings, published in the esteemed journal Nature Astronomy, expose the extraordinarily harsh environmental conditions these worlds endure and challenge pre-existing notions about their atmospheric compositions and potential habitability.
Red dwarf stars, such as TRAPPIST-1, are the smallest and coolest stellar bodies populating our Milky Way galaxy. Comprising more than 75% of all stars, they have rapidly become focal points in the search for habitable exoplanets due to the prevalence of Earth-like planets in their orbit. However, the intrinsic characteristics of red dwarfs—primarily their intense magnetic activity and stellar flares—cast doubt on whether planets in their systems can sustain atmospheres dense enough to foster life. The TRAPPIST-1 system, with its seven rocky planets closely packed in tight orbits, serves as a natural laboratory, providing an extraordinary opportunity to investigate these tantalizing questions on planetary evolution and habitability under such extreme conditions.
This year marks the tenth anniversary since the discovery of the TRAPPIST-1 system, a milestone celebrated through a dedicated observational campaign deploying the JWST’s unprecedented infrared capabilities. Specifically, researchers targeted TRAPPIST-1b and TRAPPIST-1c, the two planets closest to the star, which would logically be the most susceptible to erosive stellar effects. These continuous 60-hour observations aimed to detect thermal phase curves—a method monitoring the variation in infrared brightness as planets orbit their star—to determine the presence or absence of atmospheres by assessing surface temperature contrasts between their day and night sides.
The results were striking: both TRAPPIST-1b and TRAPPIST-1c exhibited extreme temperature disparities, with daytime surface temperatures exceeding 200°C on TRAPPIST-1b and nearing 100°C on TRAPPIST-1c, while their nights plunged to temperatures below -200°C. Such a colossal diurnal temperature gradient strongly indicates the absence of a thick atmosphere capable of redistributing heat around the planet, a function seen in planetary bodies within our own solar system, including Earth and Venus. If these planets ever harbored atmospheres, they have evidently been stripped entirely away by relentless stellar radiation and energetic particle bombardment.
Contextualizing these observations requires understanding the dynamic environment red dwarf planets inhabit. Tidally locked due to their close proximities—meaning one hemisphere perpetually faces the star while the other remains in stygian night—these planets depend heavily on atmospheric presence to moderate temperature extremes through atmospheric circulation. Without an atmosphere, the designated dayside is scorched while the nightside freezes in darkness, producing hostile conditions for any prospective biospheres. Moreover, red dwarfs unleash intense ultraviolet radiation and coronal mass ejections that erode planetary atmospheres over time, magnifying the challenge for planetary habitability.
The implications of these findings extend well beyond the peculiarities of TRAPPIST-1b and c. They fundamentally reshape our understanding of atmospheric retention on rocky exoplanets orbiting red dwarfs. Where previously the existence of Earth-sized planets within habitable zones engendered optimism about life’s potential elsewhere, these new results underscore the fragility of atmospheres under harsh stellar influence. The paradigm shifts toward recognizing that only planets orbiting at sufficient distances, potentially shielded by magnetic fields or geological mechanisms, might sustain atmospheres conducive to life.
This ongoing line of inquiry is exemplified by the JWST’s current attention to TRAPPIST-1e, a planet residing comfortably within the star’s habitable zone—the range where temperatures could allow liquid water to exist on the surface. The hope is that unlike its inner siblings, TRAPPIST-1e may have preserved an atmosphere, possibly offering a more clement environment. The parallel drawn to our solar system—with Mercury stripped bare of atmosphere close to the Sun, while Earth and Venus retain theirs—provides a compelling comparative framework in this quest.
Dr. Emeline Bolmont, associate professor at the University of Geneva and a co-author of the study, emphasizes the value of the TRAPPIST-1 system as a premier natural laboratory for comparative planetology. “The diversity of planetary conditions in this system allows us to test and refine our models of planet formation, atmospheric loss, and habitability, particularly in environments so disparate from our own,” she notes. Her enthusiasm reflects the broader scientific community’s anticipation as further JWST observations hope to unlock the mysteries of other TRAPPIST worlds.
Prof. Brice-Oliver Demory from the University of Bern, also a co-author, highlights the instrumental role JWST has played, stating, “Detecting the presence or absence of an atmosphere on tidally locked planets around red dwarf stars is a critical first step for understanding their climate dynamics and potential habitability. The TRAPPIST-1 system’s proximity and richness make it an extraordinary case study.” Their meticulous measurements of thermal phase curves not only illuminate the current state of these planets but also contribute invaluable data for simulations predicting their atmospheric evolution under extreme stellar conditions.
Technically, these observations represent a major advancement in exoplanet atmospheric science. The JWST’s Near-Infrared Camera (NIRCam) captured continuous light curves over full planetary orbits with exquisite precision, enabling scientists to discern subtle changes attributable to surface temperatures. This approach marks a leap forward from previous methods reliant on transit spectroscopy, which often struggled to separate planetary signals from host-star noise, especially for small terrestrial planets. The success of this thermal phase curve technique heralds a new era in characterizing exoplanet climates directly.
This study, while decisive for the inner TRAPPIST-1 planets, raises further intriguing questions about atmospheric variability across the system. The outer planets, subject to weaker stellar fluxes and possibly better shielded, may retain atmospheres, or even tenuous envelopes of volatile substances, sustaining more hospitable climates. Continuous observations and improved modeling efforts aim to constrain these possibilities, with forthcoming JWST campaigns expected to provide richer datasets enabling unprecedented interplanetary comparisons.
In conclusion, the comprehensive climate mapping of TRAPPIST-1b and TRAPPIST-1c fundamentally establishes that dense atmospheres are unlikely on these worlds, reshaping how scientists assess habitability in red dwarf systems. The broader implication is clear: habitability around such stars is complex, contingent not merely on location within a habitable zone but also on a fragile equilibrium between stellar activity and planetary atmospheric retention. As we probe deeper into this nearby planetary system, each discovery refines our search for life beyond Earth, underscoring the vital role cutting-edge observatories like JWST play in unraveling the universe’s greatest mysteries.
Subject of Research: Not applicable
Article Title: No thick atmosphere around TRAPPIST-1 b and c from JWST thermal phase curves
News Publication Date: 3-Apr-2026
Web References: DOI: 10.1038/s41550-026-02806-9
Keywords
Exoplanets, TRAPPIST-1, James Webb Space Telescope, Red dwarf stars, Atmospheric stripping, Thermal phase curves, Planetary habitability, Tidal locking, Rocky planets, Climate mapping, Planetary atmospheres
