Exoplanets, -moons, -comets

Impact of Clouds on the Atmosphere-Mantle Interface of Sub-Neptunes

By Keith Cowing

Status Report

astro-ph.EP

May 29, 2026

Filed under astro-ph.EP, atmosphere, climate, exoplanet, GJ 1214 b, Hycean atmosphere, PICASO 1D, Spectroscopy, sub-Neptune, TOI-1231 b, TOI-270 d

Impact of Clouds on the Atmosphere-Mantle Interface of Sub-Neptunes — Each panel shows the T(P) profiles for the clear atmosphere (red line) and cloudy atmosphere (blue line) computed for a sub-Neptune belonging to our sample of 8 sub-Neptunes. The phases of the interfaces for TOI-270 d and TOI-1231 b are shown in Figure 5, while those for the rest of the sub-Neptunes in our sample are shown here. Similar to Figure 5, the thicker lines depict the convective regions of the atmosphere. The locus of blue and red crosses show the P and T locations of the atmosphere-mantle interface computed by coupling our atmosphere model with the interior structure model for the cloudy and clear models, respectively. The P − T location and the T(P) profiles are overlaid on the phase–diagram for silicates, depicting its solid and molten phases as blue and red shaded regions. — astro-ph.EP

Sub-Neptunes are among the most common type of close-in planets found in our galaxy, yet their bulk composition remains largely uncertain; H-rich envelopes overlaying rocky cores, volatile-rich planets, and carbon-rich interiors all remain viable configurations for members of this population.

Atmospheric characterization has been proposed as a means of distinguishing between these scenarios, but growing evidence suggests that sub-Neptunes may host molten atmosphere-mantle interfaces which could alter the composition of their atmosphere. We use the PICASO 1D climate model, coupled to interior-structure and magma-atmosphere chemistry frameworks to quantify how clouds alter the atmospheric and interior structure of sub-Neptunes.

For temperate sub-Neptunes like TOI-270 d, we find that clouds can lead to ≥1000 K heating at depth (∼104 bar) and ∼600 K cooling at shallow pressures (∼1 bar). This heating is very sensitive to the cloud sedimentation efficiency and, to a lesser extent, to metallicity. Most sub-Neptunes in our sample should have a molten atmosphere-mantle interface, except TOI-1231 b and GJ 1214 b.

For these two planets, cloudy models have a molten interface whereas clear models can allow a solid boundary. Clouds can heat the atmosphere-mantle interfaces by a temperature difference between ∼1400−2600 K for most sub-Neptunes in our sample.

Such cloud-driven heating can substantially change the composition of the interface with abundances of O₂, SiH₄, and SiO showing a ≥36% increase between cloudy and clear models of TOI-270 d.

We discuss the implications of our results for the thermal evolution and measurements of intrinsic heat flux for this population.

Sagnick Mukherjee, Matthew C. Nixon, Luis Welbanks, James Mang, Nicholas F. Wogan, Natasha E. Batalha, Michael R. Line

Comments: Accepted for publication in The Astrophysical Journal Letters, Main Text: Pages 1 to 15, 8 Figures, 1 Table, Appendix: Pages 16 to 22, 4 Figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2605.27353 [astro-ph.EP] (or arXiv:2605.27353v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.27353
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Submission history
From: Sagnick Mukherjee
[v1] Tue, 26 May 2026 17:52:52 UTC (1,627 KB)
https://arxiv.org/abs/2605.27353

Astrobiology, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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