1,000-mile Martian cloud forms through never-before-observed exotic ice physics, Nature study confirms
Sorbonne researchers simulate the Arsia Mons Elongated Cloud using homogeneous nucleation—water vapor freezing directly into ice without dust particles.
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For decades, planetary atmospheric scientists have been puzzled by the daily emergence of the Arsia Mons Elongated Cloud (AMEC)—a gargantuan, wispy water-ice formation that materializes every morning near a 65,000-foot Martian volcano, stretches over 1,000 miles across the red planet's equator, and completely dissipates by noon. Now, a study published in Nature Geoscience has resolved the mystery by identifying a physical phenomenon never before observed in nature.
Lead researcher Jorge Hernández-Bernal and colleagues at Paris’ Sorbonne Université successfully created the first complete computer simulation of the cloud's atmospheric dynamics. The breakthrough required incorporating an exotic thermodynamic principle known as homogeneous nucleation: the process by which supersaturated water vapor converts directly into crystalline ice spontaneously, without relying on microscopic dust grains or mineral aerosols to seed crystal growth.
On Earth, virtually all cloud formation is heterogeneous: water vapor requires airborne condensation nuclei—such as salt spray, industrial soot, or desert dust—to overcome surface tension and coalesce into droplets or ice. While homogeneous nucleation is documented in theoretical physics textbooks, atmospheric scientists long assumed it was physically impossible to observe in real planetary atmospheres due to ambient particulate contamination.
However, the unique conditions above Arsia Mons—combining extreme high-altitude wind updrafts, plummeting temperatures below minus 190 degrees Fahrenheit, and air remarkably devoid of suspended dust—allow homogeneous nucleation to govern the cloud's rapid expansion. The findings provide vital empirical data for atmospheric climate models, establishing that planetary atmospheres can sustain cloud systems through thermodynamic pathways previously confined to theoretical laboratory chambers.