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Published September 5, 2019 | Accepted Version + Supplemental Material
Journal Article Open

Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b


Most known terrestrial planets orbit small stars with radii less than 60 per cent of that of the Sun. Theoretical models predict that these planets are more vulnerable to atmospheric loss than their counterparts orbiting Sun-like stars. 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. 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. 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 ± 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.

Additional Information

© 2019 Nature Publishing Group. Received 22 March 2019; Accepted 22 July 2019; Published 19 August 2019. Data availability: The raw data used in this study are available at the Spitzer Heritage Archive, https://sha.ipac.caltech.edu/applications/Spitzer/SHA. Code availability: We processed and fitted the data with the open-source pipeline POET, which is available at https://github.com/kevin218/POET. We used the code version corresponding to commit ID adbe62e7b733df9541231e8d1e5d32b7e2cdad76. L.K. is a Junior Fellow of the Harvard Society of Fellows. J.D. is a 51 Pegasi b Postdoctoral Fellow. A.V. is a NASA Sagan Fellow. D.D.B.K. was supported by a James S. McDonnell Foundation postdoctoral fellowship. R.H. is supported in part by NASA Grant number 80NM0018F0612. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. A.V.'s work was performed under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory, funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. D.C. acknowledges support from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. Author Contributions: L.K. conceived the project, planned the observations and carried out the primary data reduction. D.D.B.K., C.M. and R.H. ran theoretical models for the planet's atmosphere and surface. L.S. provided atmospheric evolution models. D.D., K.B.S., J.D., A.V., D.B. and X.G. contributed to the data analysis. K.S. modelled the stellar spectrum. I.C., D.C., D.W.L., A.L., G.R., S.S. and R.V. provided useful comments on the manuscript and assisted with the observing proposal. The authors declare no competing interests.

Attached Files

Accepted Version - 1908.06834.pdf

Supplemental Material - 41586_2019_1497_Fig10_ESM.jpg

Supplemental Material - 41586_2019_1497_Fig5_ESM.jpg

Supplemental Material - 41586_2019_1497_Fig6_ESM.jpg

Supplemental Material - 41586_2019_1497_Fig7_ESM.jpg

Supplemental Material - 41586_2019_1497_Fig8_ESM.jpg

Supplemental Material - 41586_2019_1497_Fig9_ESM.jpg


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August 22, 2023
October 18, 2023