Search

Most known terrestrial planets orbit small stars with radii less than 60 per cent of that of the Sun.sup.1,2. Theoretical models predict that these planets are more vulnerable to atmospheric loss than their counterparts orbiting Sun-like stars.sup.3-6. To determine whether a thick atmosphere has survived on a small planet, one approach is to search for signatures of atmospheric heat redistribution in its thermal phase curve.sup.7-10. Previous phase curve observations of the super-Earth 55 Cancri e (1.9 Earth radii) showed that its peak brightness is offset from the substellar point (latitude and longitude of 0 degrees)--possibly indicative of atmospheric circulation.sup.11. Here we report a phase curve measurement for the smaller, cooler exoplanet LHS 3844b, a 1.3-Earth-radii world in an 11-hour orbit around the small nearby star LHS 3844. The observed phase variation is symmetric and has a large amplitude, implying a dayside brightness temperature of 1,040 [plus or minus] 40 kelvin and a nightside temperature consistent with zero kelvin (at one standard deviation). Thick atmospheres with surface pressures above 10 bar are ruled out by the data (at three standard deviations), and less-massive atmospheres are susceptible to erosion by stellar wind. The data are well fitted by a bare-rock model with a low Bond albedo (lower than 0.2 at two standard deviations). These results support theoretical predictions that hot terrestrial planets orbiting small stars may not retain substantial atmospheres. Phase curve measurements for the small (1.3 Earth radii) terrestrial exoplanet LHS 3844b show absence of a thick atmosphere, in agreement with theoretical predictions., Author(s): Laura Kreidberg [sup.1] , Daniel D. B. Koll [sup.2] , Caroline Morley [sup.3] , Renyu Hu [sup.4] [sup.5] , Laura Schaefer [sup.6] , Drake Deming [sup.7] , Kevin B. [...]

Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a unique opportunity to search for atmospheres on small planets outside the Solar System 1 . Thanks to the recent launch of the James Webb Space Telescope (JWST), possible atmospheric constituents such as carbon dioxide (CO 2 ) are now detectable 2,3 . Recent JWST observations of the innermost planet TRAPPIST-1 b showed that it is most probably a bare rock without any CO 2 in its atmosphere 4 . Here we report the detection of thermal emission from the dayside of TRAPPIST-1 c with the Mid-Infrared Instrument (MIRI) on JWST at 15 µm. We measure a planet-to-star flux ratio of f p /f ⁎  = 421 ± 94 parts per million (ppm), which corresponds to an inferred dayside brightness temperature of 380 ± 31 K. This high dayside temperature disfavours a thick, CO 2 -rich atmosphere on the planet. The data rule out cloud-free O 2 /CO 2 mixtures with surface pressures ranging from 10 bar (with 10 ppm CO 2 ) to 0.1 bar (pure CO 2 ). A Venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6σ confidence. Thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. The absence of a thick, CO 2 -rich atmosphere on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with less than [Formula: see text] Earth oceans of water. If all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system., (© 2023. The Author(s).)