A massive Martian cloud forms daily over Arsia Mons, revealing new atmospheric processes. Published in Nature Geoscience, the study highlights an unobserved condensation mechanism.
Giant Martian cloud forms daily near Arsia Mons
A massive cloud stretching over 1,800 km forms each morning above the extinct Martian volcano Arsia Mons during spring and summer, according to research published in Nature Geoscience on October 7, 2026. This phenomenon, observed during the Martian seasons, is a newly discovered atmospheric process.Cloud forms through unusual condensation
The study, led by planetary scientist Jorge Hernández-Bernal from Sorbonne University, describes how the cloud forms through a condensation process not previously seen in planetary atmospheres. The cloud vanishes within a few hours and spans one twelfth of Mars' circumference.Mars Express tracks the cloud for years
The European Space Agency’s Mars Express probe has monitored the cloud since 2018 using three instruments, including its visual monitoring camera. The cloud is classified as an orographic cloud, formed when wind flows over a topographic feature like a mountain.Mountain wave drives cloud formation
The cloud forms due to a mountain wave, an atmospheric phenomenon created when wind flows over a summit. This wave lifts air rapidly, causing a sudden drop in temperature of about 30 °C in ten minutes. This cooling increases humidity, but the Martian atmosphere lacks the particles needed for typical ice formation.New model explains cloud’s size
Classical simulations failed to reproduce the cloud until researchers added a process called homogeneous nucleation, where ice forms without particles. This model now matches the observed size, shape, and timing of the cloud. While some water may come from the atmosphere, the source of the vapor remains uncertain.Process has Earth and planetary implications
Homogeneous nucleation could also occur in Earth’s high-altitude clouds, where air is dry and cold. It may apply to other planets with thin atmospheres. Confirming this would require probes that can measure water vapor inside clouds. Mars Express continues to gather data on this phenomenon, having observed Mars since 2003.
