Exoplanets, -moons, -comets

PICASO 4.0: Clouds And Photochemistry In Climate Models Of Brown Dwarfs And Exoplanets

By Keith Cowing

Status Report

astro-ph.EP

February 28, 2026

Filed under astro-ph.EP, atmosphere, brown dwarf, climate, exoplanet, imaging, PICASO

PICASO 4.0: Clouds And Photochemistry In Climate Models Of Brown Dwarfs And Exoplanets — A heatmap of Planck-weighted correlated-k tables to complement Figure 5 of PICASO 3.0 release in order to show any major differences between opacity and chemistry updates. The four panels correspond to Gauss points 1, 3, 5, and 7 (shown in the title of each panel). The dashed black lines correspond to Sonora-bobcat pressure-temperature profiles at increasing effective temperatures for reference (as labeled in the upper left panel) (Marley et al. 2021). All major features of the correlated-k tables remain the same between v3 and v4. — astro-ph.EP

We present a major update to the open-source atmospheric modeling package PICASO, designed for simulating the thermal structure and spectra of hydrogen-rich atmospheres of brown dwarfs and exoplanets.

This release, PICASO 4.0, expands upon the existing radiative-convective equilibrium model framework by incorporating several new capabilities. Key additions include the integration of Virga for self-consistent cloud modeling, new flexible treatments for rainout and cold trapping of volatile species, and support for photochemistry.

We also introduce a parameterized energy injection scheme to simulate additional external or internal heating processes. These features are motivated by lessons from recent JWST observations that reveal the prevalence of non-equilibrium chemistry and clouds.

We benchmark the new functionalities against previously published results in the literature, including the Sonora Diamondback grid, energy injected atmospheres, patchy cloud models, and other photochemical models of WASP-39b. PICASO continues to be actively developed as an open-source package aimed at enabling reproducible, community-driven atmospheric modeling of all substellar objects.

James Mang, Natasha E. Batalha, Caroline V. Morley, Nicholas F. Wogan, Sagnick Mukherjee, Channon Visscher, Mark S. Marley, Jonathan J. Fortney, Katy L. Chubb, Peter Gao, Isaac Malsky

Comments: Accepted in ApJ. Code available here: https://github.com/natashabatalha/picaso along with documentation here: https://natashabatalha.github.io/picaso /
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2602.22468 [astro-ph.EP] (or arXiv:2602.22468v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2602.22468
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Submission history
From: James Mang
[v1] Wed, 25 Feb 2026 23:07:50 UTC (1,226 KB)
https://arxiv.org/abs/2602.22468
Astrobiology, Astrochemistry

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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