Hot Rocks Survey

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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 1.65σ, 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 3σ. 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.
Funding Information
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (P500PT_225456/1)
  • Swiss State Secretariat for Education (MB22.00046)
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (51NF40\_205606)
  • Carlsberg Foundation (CF22-1254)
  • Horizon Europe Guarantee Fund (EP/Z00330X/1)
  • National Science Foundation Graduate Research Fellowship Program (DGE1746891)
  • European Research Council (805445)
  • Science Foundation Ireland (URF\R\201032)
  • eSSENCE (eSSENCE@LU 9:3)
  • Crafoord Fundation
  • The Fund of the Walter Gyllenberg Foundation
  • Carlsberg Foundation (CF22-1548)

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