Kreidberg, LauraHu, RenyuSchaefer, LauraDeming, DrakeStevenson, Kevin B.Dittmann, JasonVanderburg, AndrewBerardo, DavidGuo, XueyingStassun, KeivanCrossfield, IanCharbonneau, DavidLoeb, AbrahamRicker, GeorgeSeager, SaraVanderspek, RolandKoll, DanielMorley, CarolineLatham, David2020-01-232019-08-19Laura Kreidberg, Daniel D. B. Koll, Caroline Morley, Renyu Hu, Laura Schaefer, Drake Deming, Kevin B. Stevenson, Jason Dittmann, et al. 2019. Absence of a Thick Atmosphere on the Terrestrial Exoplanet LHS 3844b. Nature 573: 87–90.0028-08361476-4687http://nrs.harvard.edu/urn-3:HUL.InstRepos:42241194The majority of terrestrial planets in the Galaxy orbit small stars with radii less than 60% that of the Sun1,2. Theoretical models predict that these planets are more vulnerable to at- mospheric escape and collapse than their counterparts orbiting Sun-like stars3–5. To deter- mine whether a thick atmosphere has survived, one approach is to search for signatures of atmospheric heat redistribution in a planet’s thermal phase curve6–9. This technique was previously applied to the super-Earth 55 Cancri e, which showed an offset hot spot indicative of atmosphere heat circulation10. Here we report a phase curve measurement for the exo- planet LHS 3844b, a 1.3 R⊕ world in an 11-hour orbit around a small, nearby star. This is the first such measurement for a planet smaller than 1.6 Re, the size marking the transition from rocky to gaseous worlds11. The phase variation is symmetric and has a large amplitude, implying a dayside brightness temperature of 1040±40 K and a nightside temperature con- sistent with zero K (1σ confidence). The data are best fit by a bare rock model with a low Bond albedo (< 0.2 at 2σ confidence), or a tenuous atmosphere with surface pressure below 0.1 bar. These results support theoretical predictions that hot terrestrial planets orbiting small stars may not retain substantial atmospheres.en-USMultidisciplinaryJournal Article2020-01-2310.1038/s41586-019-1497-4