Mars' Giant Arsia Mons Cloud: 1,800 km Daily Phenomenon 2026

The Arsia Mons Elongated Cloud (AMEC) is a gigantic cloud on Mars that appears every morning, stretches over 1,800 kilometers, and vanishes by the afternoon. This daily phenomenon has intrigued scientists for years, and recent research reveals it forms under conditions never before seen on the Red Planet.

Unlike typical clouds, AMEC is an orographic cloud—created when wind hits a mountain—and it forms around the Arsia Mons volcano in the southern hemisphere during spring and summer. Discovered in 2018 by the Mars Express orbiter, the cloud was further described in a 2021 study using Mars Express images. Since then, astronomers have been eager to understand its peculiar behavior.

What Is the Arsia Mons Elongated Cloud?

AMEC is a orographic cloud, meaning it forms when wind is forced upward by a mountain, cooling and condensing water ice. On Earth, such clouds are common, but on Mars, they are rare due to the thin, dry atmosphere. The cloud typically emerges before dawn, grows rapidly, and dissipates by midday.

Its size is staggering: at its peak, AMEC can span up to 1,800 kilometers in length, making it one of the largest clouds ever observed on Mars. This daily cycle repeats for months, driven by the Martian seasons.

Why Scientists Are Puzzled

The mystery deepens because existing cloud formation models cannot reproduce AMEC's behavior. On Earth, clouds need condensation nuclei—tiny particles like dust or salt—to form. On Mars, similar particles are scarce, yet AMEC forms without them. This suggests a unique mechanism at play.

Researchers from the University of the Basque Country and the Sorbonne University in Paris have been studying this anomaly. Their findings indicate that the cloud originates under conditions totally unexpected for Mars, challenging our understanding of atmospheric processes on the planet.

How Does AMEC Form?

The leading hypothesis involves gravity waves—oscillations in the atmosphere triggered by wind passing over the volcano. These waves can create localized cooling, allowing water ice to condense even without seeds. However, the exact process remains unclear.

Another factor is the volcano's height: Arsia Mons rises about 20 kilometers, towering over the surrounding plains. As wind hits this massive obstacle, it is forced upward, leading to rapid cooling and cloud formation. The daily cycle is driven by temperature changes from dawn to afternoon.

Key Takeaways

• AMEC is a daily orographic cloud on Mars that stretches up to 1,800 km.
• It forms around Arsia Mons volcano during spring and summer, disappearing by afternoon.
• Scientists are baffled because the cloud forms without condensation nuclei.
• Research suggests gravity waves and the volcano's height play crucial roles.
• Understanding AMEC could improve models of Martian climate and atmospheric dynamics.

Comparison with Earth Clouds

What’s Next for AMEC Research?

Future missions, including the European Space Agency's ExoMars and NASA's Mars 2020 Perseverance rover, may provide more data on Martian clouds. However, AMEC is best observed from orbit, and current orbiters like Mars Express and MAVEN continue to monitor it. The background to this story is set out in Science: latest articles.

Scientists hope to refine models by incorporating gravity wave dynamics and surface-atmosphere interactions. This could not only explain AMEC but also enhance our understanding of climate on other planets. A related thread runs through Amazon's Foldable Prefab House: Bedroom, Kitchen, Bath for €6,299. Earlier coverage in Mars' Giant Arsia Mons Cloud: 1,800 km Daily Phenomenon shows how the argument developed.