Scientists Replicate Mars Cloud Using Physics Long Considered Theoretical

A new computer model successfully reproduces the formation of a massive cloud on Mars by applying a physical process that scientists previously believed did not occur in nature. The study, published in Nature Geoscience, offers the first plausible explanation for a feature that has puzzled researchers since its discovery.

The Arsia Mons Elongated Cloud, or AMEC, appears each morning during the Martian spring and summer. It forms near the Arsia Mons volcano and stretches across more than 1,000 miles before dissipating. This cycle repeats over several months, covering a distance comparable to the straight-line route from New York to Kansas City.

A probe first detected the cloud in 2018. For eight years, scientists struggled to explain its existence using standard atmospheric models. The new work by researchers at Sorbonne Université in Paris solved the puzzle by incorporating what lead author Jorge Hernández-Bernal described as exotic physics. This process, known as homogeneous nucleation, involves water vapor turning directly into ice crystals without dust or salt particles to seed the reaction.

Hernández-Bernal noted that while this mechanism appears in textbooks, it is usually treated as theoretical. He compared it to condensation forming in the middle of a room rather than on a window. The simulations only worked when the researchers included this specific physics, which he called wholly unexpected.

The volcano plays a central role in creating the necessary conditions. When wind hits the 65,000-foot peak, it generates a wave that lifts moist air high into the atmosphere. This rapid ascent causes a temperature drop of 30 degrees Celsius within 10 minutes. The process requires relative humidity levels more than 100,000 times higher than any value measured on Earth.

Scientists had long assumed similar nucleation might occur in the upper atmospheres of Venus and Earth, but it had never been observed. The extreme humidity required explains why the phenomenon remained hidden on Earth. Hernández-Bernal stated that the result is remarkable because far less is known about the Martian atmosphere than the one on Earth.

The study confirms that such extreme humidity conditions exist on Mars, a fact previously unknown to researchers. The successful replication of the cloud in the model marks a major step in understanding Martian weather patterns.