Martian volcano produces giant ice cloud

Each austral spring, a massive plume of ice forms above the Martian volcano Arsia Mons, stretching nearly 1,800 kilometers before vanishing within hours. This phenomenon, called the Arsia Mons Elongated Cloud (AMEC), is the largest known orographic cloud in the Solar System.

Cloud forms in a predictable cycle

The cloud appears before dawn, extends over two to three hours, and disappears by noon. This pattern has been observed by the Mars Express spacecraft for more than a decade, revealing a consistent and mysterious atmospheric event.

New simulations reveal a unique process

Recent simulations suggest the cloud forms through homogeneous nucleation, a theoretical process where water vapor directly transforms into ice without needing a surface to start crystallization. This mechanism, previously unobserved in nature, was confirmed using data from Mars Express.

Volcano's role in the phenomenon

Arsia Mons, a 20-kilometer-high volcano in Mars' southern hemisphere, creates the conditions for this cloud. During spring and summer, air masses are forced upward by the volcano’s terrain, creating a wave-like motion that leads to the formation of the cloud.

Earlier models failed to explain the cloud

A 2022 study described a cloud model with a head of 120 kilometers and a tail over 1,000 kilometers. However, it did not match real observations, particularly the cloud’s optical depth and the length of its tail.

New simulations include key ingredient

To better match the observed AMEC, researchers added homogeneous nucleation to their models. This theoretical process, now validated by comparisons with Mars Express data, explains how the cloud forms and stretches so far.

Discovery has broader implications

The finding suggests that a mechanism long confined to physics textbooks can manifest on a large scale in the Martian atmosphere. It highlights how Mars continues to provide unexpected insights into planetary meteorology.