Homogeneous Nucleation of Water Vapor Evidenced by Elongated Clouds on Mars

[astro-ph.EP] It is widely accepted that water vapor forms clouds by heterogeneous nucleation (condensation on pre-existing dry nuclei).

Homogeneous nucleation (directly from water vapor, without a pre-existing nuclei) is theoretically possible, but it requires high levels of supersaturation and so it is not considered a viable cloud formation process under real atmospheric conditions.

Here, we show that introducing homogeneous nucleation in a meteorological model of Mars allows to successfully reproduce the unique characteristics of the Arsia Mons Elongated Cloud, a remarkable water ice cloud that occurs recurrently on Mars and which had remained impossible to model under conventional cloud microphysics.

This finding demonstrates that homogeneous nucleation happens on Mars, provides the first evidence of homogeneous nucleation of water vapor in a planetary atmosphere, and challenges current assumptions about cloud formation processes, which is also relevant for certain clouds on Earth and potentially on other planets.

J. Hernandez-Bernal, A. Maattanen, A. Spiga, F. Forget

Comments: This preprint has not undergone peer review or any post-submission improvements or corrections
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.37259 [astro-ph.EP] (or arXiv:2609.37259v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.37259
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Related DOI:
https://doi.org/10.1038/s41561-026-02089-9
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Submission history
From: Jorge Hernández-Bernal
[v1] Tue, 29 Sep 2026 11:10:34 UTC (3,974 KB)
https://arxiv.org/abs/2609.37259

Astrobiology,