# Mars Cloud Forms Via Never-Before-Seen Ice Physics

> A 1,100-mile cloud on Mars forms through a unique process where water vapor freezes without dust particles, a phenomenon previously unobserved in any planetary atmosphere.

By PrimaryBrief newsroom · Published 2026-10-24T12:42:55.506139Z
Canonical: https://primarybrief.com/article/mars-cloud-forms-via-never-before-seen-ice-physics-9bb22d8f

A study published on October 7, 2026, in *Nature Geoscience* revealed that the 1,100-mile-long Arsia Mons Elongated Cloud (AMEC) on Mars forms through a process called homogeneous nucleation, marking the first observation of this phenomenon in a planetary atmosphere [2][4][5]. The research, led by Jorge Hernández-Bernal of LMD/CNRS/Sorbonne Université in Paris, explains how water vapor directly freezes into ice crystals without requiring dust particles as seeds [1][4][5].

This discovery changes scientific understanding of cloud formation beyond Earth. It highlights how drastically atmospheric processes can differ between planets, offering new insights for future studies of extraterrestrial environments and challenging existing assumptions about how clouds form [2][10][11].

## What the records show
Researchers analyzed data from the European Space Agency's Mars Express orbiter, specifically using its Visual Monitoring Camera (VMC), High Resolution Stereo Camera (HRSC), and OMEGA spectrometer [8][12][13][14]. Their simulations demonstrated that winds rising along the slopes of the 12-mile-high Arsia Mons volcano can cause temperatures to drop by approximately 54 degrees Fahrenheit (30 degrees Celsius) in about 10 minutes [2][5][9]. This rapid cooling leads to extreme humidity levels, soaring to "ten million percent" and becoming roughly 100,000 times higher than typical Earth conditions [2][4][9]. In this dust-scarce environment, with only 0.1 dust grains per cubic centimeter in the Martian summer atmosphere, water vapor spontaneously freezes into ice crystals [4][7]. Earlier attempts to model the AMEC using conventional cloud physics failed to reproduce its features [6][7][9][10][11]. The new model, incorporating homogeneous nucleation, successfully replicated the cloud's unique characteristics [10][11].

## The timeline
The Arsia Mons Elongated Cloud is a recurring feature, appearing almost daily during Martian spring and summer, developing each morning and dissipating by evening [2][6][9]. The European Space Agency's Mars Express orbiter first imaged this curious cloud in 2018 [9]. The study detailing its formation mechanism was published in *Nature Geoscience* on October 7, 2026 [2][4][5].

## What changed and for whom
For planetary scientists, the identification of homogeneous nucleation provides a long-sought explanation for the AMEC, which had puzzled researchers for decades [7][9]. This marks the first observed instance of water vapor freezing without requiring a pre-existing particle in any planetary atmosphere, a process previously considered theoretical in nature for such conditions [5][10]. The finding suggests that planetary atmospheres can host more varied and exotic physical processes than previously confirmed.

## What the subject has said publicly
Lead author Jorge Hernández-Bernal stated that the study "provides the first observation of homogeneous nucleation in a planetary atmosphere" [2]. He further emphasized the novelty, saying, "We call this homogeneous nucleation, and we've never seen it before in a planetary atmosphere" [4][5]. Hernández-Bernal explained that the cloud forms without needing "any of this 'stuff'," referring to seed particles, and compared it to condensation appearing in the middle of a room [4][6].

## What we could not confirm
The study infers the homogeneous nucleation mechanism from modeling and observations, rather than directly observing the process in action [5][6]. Although the simulations reproduce key features of the AMEC, the authors note that some mismatches with actual measurements still exist [6]. It also remains unclear why a similar cloud formation does not occur over Olympus Mons, a significantly taller Martian volcano [9].

## Evidence cited
1. A 1,000 Mile Cloud On Mars May Reveal Physics Never Seen In Nature: A 1,000-mile cloud on Mars may reveal physics never seen in nature (orbitalrecord.com) — https://orbitalrecord.com/
2. Mars' Giant Arsia Mons Cloud Is Stranger Than Scientists Thought (tippinsights.com) — https://tippinsights.com/
3. Homogeneous ice nucleation from water vapour suggested by elongated clouds on Mars (researchgate.net) — https://researchgate.net/
4. Mars Cloud Reveals Never-Before-Seen Ice Formation Physics (orbital-wire.com) — https://orbital-wire.com/
5. Mars' 1,100-Mile Cloud Forms Through Never-Before-Seen Physics (natureworldnews.com) — https://natureworldnews.com/
6. Mars Cloud Forms Through 'Exotic Physics' Never Before Seen In Nature (thebrighterside.news) — https://thebrighterside.news/
7. A 1,800 km Long Cloud on Mars Forms by “Flash-Freezing out of Thin Air” (universetoday.com) — https://universetoday.com/
8. Mars Cloud Forms From "Exotic Physics" Never Before Seen in a Planetary Atmosphere (scitechdaily.com) — https://scitechdaily.com/
9. How Mars's "Weirdest Cloud" Gets Its Start (skyandtelescope.org) — https://skyandtelescope.org/
10. Homogeneous ice nucleation from water vapour suggested by elongated clouds on Mars (ip-paris.fr) — https://ip-paris.fr/
11. Homogeneous ice nucleation from water vapour suggested by elongated clouds on Mars (arxiv.org) — https://arxiv.org/
12. A new paper offers new insights into Mars’ weirdest cloud (earthsky.org) — https://earthsky.org/
13. A mechanism without dust particles (ua.news) — https://ua.news/
14. Mars' Massive Cloud Mystery Solved, Explains "Exotic Physics" (discovermagazine.com) — https://discovermagazine.com/
15. Repurposing Mars Express’s webcam for science (esa.int) — https://esa.int/
16. Le "nuage sans poussière" de Mars est le premier exemple d'un phénomène « exotique » (sciencepost.fr) — https://sciencepost.fr/