Exoplanets, -moons, -comets

Hot Rocks Survey II: The Thermal Emission Of TOI-1468 b Reveals A Hot Bare Rock

By Keith Cowing
Status Report
astro-ph.EP
March 27, 2025
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Hot Rocks Survey II: The Thermal Emission Of TOI-1468 b Reveals A Hot Bare Rock
Emission spectra for different atmospheric scenarios. The curves show the planetary flux to stellar flux ratio in ppm as a function of wavelength in µm. In all cases we considered a surface albedo of 0.1, heat redistribution factor based on Koll (2022) and colour-coded in the legend, ordered by the corresponding location of the model in the 15 µm bandpass. Only the no atmosphere cases have an albedo of 0 and 0.1 and zero heat redistribution. The grey dashed line and the shaded area is the blackbody emission at 1024 K and 1σ confidence interval. The black dot is the measured joint occultation depth with its 1σ uncertainty, while the pink diamond is the measured value from the independent analysis using Frida. The blue curve and light blue shaded area at the bottom is the response function of the F1500W filter. — astro-ph.EP

Terrestrial exoplanets orbiting nearby small, cool stars known as M dwarfs are well suited for atmospheric characterisation. Given the strong XUV irradiation from M dwarf host stars, orbiting exoplanets are thought to be unable to retain primordial H/He-dominated atmospheres.

However, the survivability of heavier secondary atmospheres is currently unknown. The aim of the Hot Rocks Survey programme is to determine if exoplanets can retain secondary atmospheres in the presence of M dwarf hosts. Among the sample of 9 exoplanets in the programme, here we aim to determine whether TOI-1468 b has a substantial atmosphere or is consistent with a low-albedo bare rock.

The James Webb Space Telescope provides an opportunity to characterise the thermal emission with MIRI at 15 μm. TOI-1468 b’s occultation was observed three times. We compare our observations to atmospheric models including varying amounts of CO2 and H2O. The observed occultation depth 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 zero Bond albedo at 1.65-σ confidence level 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 over 3-σ. Surprisingly, TOI-1468 b presents a surface marginally hotter than expected, hinting at an additional source of energy on the planet.

It could originate from a temperature inversion, induction heating or be an instrumental artifact. 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 on M dwarfs recently approved by the STScI.

E.A. Meier Valdés, B.-O. Demory, H. Diamond-Lowe, J.M. Mendonça, P.C. August, M. Fortune, N.H. Allen, D. Kitzmann, A. Gressier, M. Hooton, K.D. Jones, L.A. Buchhave, N. Espinoza, C.E. Fisher, N.P. Gibson, K. Heng, J. Hoeijmakers, B. Prinoth, A.D. Rathcke, J.D. Eastman

Comments: 18 pages, 10 figures. Accepted for publication on A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2503.19772 [astro-ph.EP] (or arXiv:2503.19772v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2503.19772
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Submission history
From: Erik Andreas Meier Valdés
[v1] Tue, 25 Mar 2025 15:43:47 UTC (8,953 KB)
https://arxiv.org/abs/2503.19772
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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