Mars Express Unveils Secrets of the Arsia Mons Elongated Cloud
Date: 07/10/2026
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Researchers using the European Space Agency’s Mars Express spacecraft, combined with advanced meteorological models, have discovered unusual atmospheric physics behind Mars’s most fascinating cloud—the Arsia Mons Elongated Cloud (AMEC).
The Spectacle of AMEC
Every spring and summer in Mars’s southern hemisphere, during the dusty season, the AMEC emerges, stretching up to 1,800 km long, nearly twice the length of the UK. Formed of water ice, this cloud develops downwind of the 20-km-tall Arsia Mons volcano and dissipates within hours, repeating this daily cycle. First identified by Mars Express in 2018, its evolution and dynamics have captivated researchers.
Unexpected Formation Physics
Jorge Hernández-Bernal from LMD/CNRS/Sorbonne Université explains that previous models failed to accurately recreate the AMEC until they incorporated “exotic physics” rarely observed in nature. Traditional cloud formation relies on heterogeneous nucleation, where water vapor condenses onto particles. However, the AMEC forms through homogeneous nucleation, where water vapor directly freezes into ice, bypassing the need for airborne particles.
Remarkable Atmospheric Conditions
Hernández-Bernal noted that this phenomenon forms under extreme conditions—requiring humidity levels hundreds of thousands of times above what humans experience on Earth. The study suggests that Mars’s thin atmosphere and the towering Arsia Mons combine to create the right environment for this unique cloud formation.
Mechanics of AMEC Creation
As winds pass over Arsia Mons, they trigger waves that lift humid air rapidly. This process can cool the atmosphere by 30 degrees within ten minutes, causing water vapor to freeze and form clouds.
The Model’s Success
While some modeled aspects diverge from observed data, Hernández-Bernal views the findings as significantly contributing to our understanding of Martian atmospheric processes. Mars Express has provided invaluable data with its trio of cameras, allowing it to monitor rapid changes in AMEC’s structure.
Looking Ahead
This study not only deepens our understanding of atmospheric phenomena on Mars but also highlights that unconventional processes should not be overlooked in planetary science, including studies of exoplanets.
For the complete research details, check out the publication: Homogeneous ice Nucleation from Water Vapour Suggested by Elongated Clouds on Mars in Nature Geoscience.
For inquiries:
ESA Media Relations
Email: media@esa.int
Explore the astonishing findings and implications of Mars Express’s observations of AMEC.
