Atmospheres, Climate, Weather

Hot And cloudy: High Temperature Clouds In Super-Earths And Sub-Neptunes

By Keith Cowing

Status Report

astro-ph.EP

January 26, 2026

Filed under 55 Cnc e, astro-ph.EP, atmosphere, Clouds, exoplanet, rocky exoplanet, Spectroscopy, sub-Neptune, super -Earth

Hot And cloudy: High Temperature Clouds In Super-Earths And Sub-Neptunes — Mass mixing ratios and condensate/cloud of the O2/CO2 atmosphere – model 5. The 15 major gas phase species are shown in the left hand side column and the solid and liquid species in the right hand side column. The upper row shows the chemistry computed with the rainout approach with FastChem3.For comparative purposes to ExoLyn we have converted the standardised output of volume mixing ratios to mass mixing ratios. In the bottom row, we have computed the cloud mass mixing ratios, particle sizes and the gas phase with the cloud formation model ExoLyn and FastChem3 combined as described in section 3.3. The grey curve in the cloud panel indicates the particle size, and the coloured lines represent the mass mixing ratios of the individual cloud components. — astro-ph.EP

JWST observations provide for the first time evidence for an atmosphere on a rocky exoplanet – 55 Cnc e. The atmosphere of 55 Cnc e is hot with T_eq>2000K and shows strong variability, for which cloud formation above a molten crust could be one possible explanation.

The composition of the atmosphere of 55 Cnc e is still unknown but suggests the presence of volatiles. We have run cloud formation models on a grid of N-dominated, O-dominated, C-dominated and H-dominated atmospheres to investigate which type of cloud we could expect on hot super-Earths and hot sub-Neptunes (1000K < T < 3000K). Our models combine radiative transfer with equilibrium chemistry of the gaseous and condensed phases, vertical mixing of condensable species, sedimentation, nucleation and coagulation.

We find that the condensability of species is highly dependent on the oxygen abundance of an atmosphere. Oxygen poor atmospheres can be heated by UV and optical absorbers PS, TiO and CN which create temperature inversions. These inhibit condensation. Oxygen rich atmospheres are colder without temperature inversions, and are therefore more favourable environments for cloud formation.

The major expected cloud component in O-dominated atmospheres with solar refractory abundance is TiO₂(s). Spectral features of clouds in these worlds are stronger in transmission than in emission, in particular at short wavelengths. We find a lack of optical data of solid species in comparison to the variety of stable cloud components which can form on hot, rocky planets.

Leoni J. Janssen, Yamila Miguel, Michiel Min, Helong Huang, Mantas Zilinskas, Christiaan P. A. van Buchem

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2601.15927 [astro-ph.EP] (or arXiv:2601.15927v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2601.15927
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Submission history
From: Leoni Janssen
[v1] Thu, 22 Jan 2026 13:05:07 UTC (8,706 KB)
https://arxiv.org/abs/2601.15927
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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