Valdés, E.A. Meier, Demory, B.-O., Diamond-Lowe, H., Mendonça, J.M., August, P.C., Fortune, M., Allen, N.H., Kitzmann, D., Gressier, A., Hooton, M., Jones, K.D., Buchhave, L.A., Espinoza, N., Fisher, C.E., Gibson, N.P., Heng, K., Hoeijmakers, J., Prinoth, B., Rathcke, A.D. and Eastman, J.D. (2025) Hot Rocks Survey II. the thermal emission of TOI-1468 b reveals a bare hot rock. A&A, 698, [A68]. (doi:10.1051/0004-6361/202453449).
Abstract
Context: terrestrial exoplanets orbiting nearby small cool stars, known as M dwarfs, are well suited for an atmospheric characterisation. Because the intense X-ray and UV (XUV) irradiation from M dwarf host stars is strong, orbiting exoplanets are thought to be unable to retain primordial hydrogen- or helium-dominated atmospheres. However, it is currently unknown whether heavier secondary atmospheres can survive.
Aims.: the aim of the Hot Rocks Survey programme is to determine whether exoplanets can retain secondary atmospheres in the presence of M dwarf hosts. In the sample of nine exoplanets in the programme, we aim to determine whether TOI-1468 b has a substantial atmosphere or is consistent with a low-albedo bare rock.
Methods: the James Webb Space Telescope provides an opportunity to characterise the thermal emission with MIRI at 15 μm. The occultation of TOI-1468 b was observed three times. We compared our observations to atmospheric models that include varying amounts of CO2 and H2O.
Results: the observed occultation depths for the individual visits are 239±52 ppm, 341±53 ppm, and 357±52 ppm. A joint fit yields an occultation depth of 311±31 ppm. The thermal emission is mostly consistent with no atmosphere and a zero Bond albedo at a confidence level of 1.65, or a blackbody at a brightness temperature of 1024 ± 78 K. A pure CO2 or H2O atmosphere with a surface pressure above 1 bar is ruled out at higher than 3.
Conclusions: surprisingly, the surface of TOI-1468 b is marginally hotter than expected. This indicates an additional source of energy on the planet. This source might originate from a temperature inversion or induction heating, or it might be an instrumental artefact. The results within the Hot Rocks Survey build on the legacy of studying the atmospheres of exoplanets around M dwarfs. The outcome of this survey will prove useful to the large-scale survey of M dwarfs that was recently approved by the STScI.
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