NASA/R. Hurt/T. Pyle
Artist’s representation shows TRAPPIST-1 and its planets reflected on a surface
New observations of TRAPPIST-1 b and TRAPPIST-1 c suggest that the two planets in the iconic TRAPPIST-1 system, which have a permanent day on one side and a permanent night on the other, do not have dense atmospheres.
An international team including the University of Bern (UNIBE) and the University of Geneva (UNIGE), members of NCCR PlanetS (National Center of Competence in Research PlanetS), has managed, for the first time, to map the climate of rocky exoplanets with masses similar to Earth.
This important advancement is based on ongoing observations with the James Webb Space Telescope.
The two planets studied belong to the iconic planetary system, discovered ten years ago. This is a real laboratory for scientists who study life in the Universe, particularly around red dwarf stars.
The two planets do not appear to have atmospheres, as observations reveal temperature differences between day and night exceeding 500 degrees Celsius. The results were published in the journal Nature Astronomy.
Red dwarf stars – cooler and smaller than our Sun – make up more than 75% of the stars in our Galaxy. Astronomers demonstrated that Small, Earth-like planets are common around this type of star.
Consequently, the question of emergence of life on these worldsso different from ours, quickly became a central issue.
Among the planetary systems discovered around red dwarfs, TRAPPIST-1, which celebrates its tenth anniversary this year, occupies a place of distinction. prominence in scientific research.
Astronomers marked this anniversary with an observation campaign using the James Webb Space Telescope (JWST), focusing on the system’s two innermost planets, TRAPPIST-1 b and TRAPPIST-1 c.
These continuous observations ruled out the hypothesis of dense atmospheres on both planets, confirming that adverse conditions around these stars can influence planetary evolution.
“The TRAPPIST-1 system is incredible! Seven planetssome with masses similar to Earth, orbit the same star”, notes Emeline Bolmontprofessor in the Department of Astronomy at the Faculty of Sciences, director of the CVU (Centre for Life in the Universe) at UNIGE and co-author of the study.
“At least three planets are located in star’s habitable zonewhere surface temperatures would allow the presence of liquid water. It is the perfect field of study for comparative planetology, unraveling the mysteries of this type of planet and testing our hypotheses about the development of life around these stars”, adds the researcher.
Energy bombings
Although red dwarf stars and their planets are common in our Galaxy, their habitability is not necessarily guaranteed. Firstly, these stars are very active and bombard their planets with intense ultraviolet radiation and streams of energetic particles, which could corrode their atmospheres and eradicate any life that might exist.
Second, planets in a red dwarf’s habitable zone orbit very close to their star, and tidal forces they synchronize their rotation with their orbital period, as happens with the Moon and the Earth.
These planets, therefore, complete a rotation around their axis at the same time as they orbit their star. The result is a permanent day on one side and a permanent night in the other.
“The presence of an atmosphere around these tidally coupled planets could allow the transfer of energy between the day and night sides, resulting in more moderate temperatures across the planet, with a significant impact on their potential habitability,” he adds. Brice-Olivier Demory, professor and director of UNIBE, co-author of the study.
“Successfully detecting the atmosphere of one of these planets has therefore become a fundamental objective for our community, highlighting the importance of the TRAPPIST-1 system with JWST”, explains Demory.
Sixty hours of TRAPPIST-1 observations
Observations with JWST involved continuously observing the two planets closest to the star, and therefore most exposed to its influence, in infrared light over a complete orbit.
These 60 hours of observations allowed scientists, for the first time, map the climate of planets the size of the Earth.
By measuring the flux of light coming from TRAPPIST-1 and planets “b” and “c”, astronomers were able to determine the surface temperatures of both planets with great precision, both on the day and night sides.
The two planets have a significant temperature difference between its two hemispheres. During the day, the surface temperatures of the two planets exceed 200°C and 100°C, respectively, while the nights are plunged into freezing temperatures below -200°C.
This enormous contrast suggests a lack of energy redistribution between the two sides of the planets and, consequently, the absence of atmospheres. If the two planets had atmospheres during their formation, these were completely eliminated by the extreme conditions imposed by their star.
The search continues
The absence of a dense atmosphere on the two inner planets of the TRAPPIST-1 system supports the hypothesis that the intense radiation and energetic ejections from red dwarfs play a significant role in the evolution of planets around this type of star.
What about the slightly more distant planetslocated in the habitable zone? The Webb Telescope is currently observing the system’s planet “e”, which lies within the star’s habitable zone – the region where liquid water may exist on the surface.
“TRAPPIST-1 serves as a reference system. Our theoretical models show that the outermost planets of the TRAPPIST-1 system may have an atmosphere, despite this absence on the two inner planets”, says Emeline Bolmont.
“This is similar to Mercurythe closest planet to our Sun, which has no atmosphere, while Venus and Earth have kept theirs. We look forward to continuing the exploration of the TRAPPIST-1 system!”, concludes the researcher.
