Recent observations from the James Webb Space Telescope (JWST) targeting the exoplanets TRAPPIST-1b and TRAPPIST-1c have revealed extreme temperature disparities, presenting the inaugural detailed climatic profiles of rocky exoplanets. These findings significantly diminish prospects for habitability on these celestial bodies.
This artist’s impression shows an imagined view from the surface one of the three exoplanets orbiting the ultracool dwarf star TRAPPIST-1 38.8 light-years from Earth. These alien worlds have sizes and temperatures similar to those of Venus and Earth. In this view one of the inner planets is seen in transit across the disc of TRAPPIST-1. Image credit: M. Kornmesser / ESO.
Red dwarf stars, characterized by their smaller stature and lower temperatures compared to our Sun, constitute over 75% of the stellar population within the Milky Way galaxy.
Astrophysicists have ascertained that planets comparable in size to Earth are remarkably prevalent in orbit around these less luminous stars, thereby posing a critical inquiry: could life emerge on worlds so profoundly dissimilar to our own?
The TRAPPIST-1 system has emerged as a pivotal locus for this ongoing scientific investigation.
This stellar arrangement, identified in 2017, is situated approximately 38.8 light-years distant within the celestial sphere of Aquarius.
Its configuration comprises seven planets that transit across their host star’s face: TRAPPIST-1b, c, d, e, f, g, and h.
These planetary bodies are all roughly analogous in dimension to Earth and Venus, or marginally smaller, and exhibit extremely abbreviated orbital periods.
“The TRAPPIST-1 system is truly remarkable! Seven planets, some possessing masses akin to Earth’s, are in orbit around a single star,” remarked Emeline Bolmont, an astronomer affiliated with the University of Geneva (UNIGE).
“A minimum of three planets are situated within the star’s habitable zone, a region where surface temperatures theoretically permit the existence of liquid water.”
“This system represents an ideal laboratory for comparative planetology, enabling us to decipher the enigmas associated with this class of planet and to validate our hypotheses regarding life’s potential development around such stars.”
Dr. Bolmont and her research team leveraged the observational capabilities of the James Webb Space Telescope (operated jointly by NASA, ESA, and CSA) to scrutinize the two innermost planets of the system: TRAPPIST-1b and TRAPPIST-1c.
“While red dwarf stars and their associated planets are widespread throughout our galaxy, their capacity to sustain life is not inherently assured,” the researchers stated.
“Primarily, these stars undergo periods of intense activity, subjecting their planets to potent ultraviolet radiation and energetic particle fluxes. Such bombardment could potentially strip away planetary atmospheres and eliminate any nascent life forms.”
“Secondly, planets residing within the habitable zone of a red dwarf are positioned in very close proximity to their star. Gravitational forces can lead to tidal locking, synchronizing their rotational period with their orbital period, much like the Moon’s relationship with Earth.”
“Consequently, these planets complete a single rotation on their axis concurrently with their orbital revolution around their star. This phenomenon results in perpetual daylight on one hemisphere and perpetual darkness on the opposing hemisphere.”
This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. Image credit: NASA / R. Hurt / T. Pyle.
Through the meticulous measurement of light emitted by both the star and the two studied planets, the astronomers successfully determined the surface temperatures of TRAPPIST-1b and TRAPPIST-1c with exceptional accuracy, differentiating between their illuminated and shadowed sides.
On their sun-facing sides, the surface temperatures of these two planets reach upwards of 200 degrees Celsius and nearly 100 degrees Celsius, respectively. Their nocturnal hemispheres, however, plunge into abyssal coldness, falling below -200 degrees Celsius.
This profound thermal differential strongly indicates a deficiency in heat distribution between the planetary hemispheres, suggesting the absence of substantial atmospheres.
It is posited that if atmospheres were present during these planets’ formation, they have been entirely eradicated by the extreme environmental conditions imposed by their parent star.
The research team posits that the lack of a dense atmosphere on the two inner planets of the TRAPPIST-1 system corroborates the theory that intense stellar radiation and energetic outbursts from red dwarf stars play a pivotal role in shaping planets orbiting such stars.
“The TRAPPIST-1 system serves as a crucial reference point. Our theoretical models indicate that the more distant planets within the TRAPPIST-1 system may indeed possess atmospheres, despite the absence thereof on the two inner planets,” Dr. Bolmont elaborated.
“This scenario is analogous to Mercury, the planet closest to our Sun, which lacks an atmosphere, while Venus and Earth have managed to retain theirs.”
“We eagerly anticipate continuing our exploration of the TRAPPIST-1 system.”
These pivotal findings were formally presented on April 3rd in the esteemed scientific journal, Nature Astronomy.
_____
M. Gillon et al. No thick atmosphere around TRAPPIST-1 b and c from JWST thermal phase curves. Nat Astron, published online April 3, 2026; doi: 10.1038/s41550-026-02806-9
