Martian Cloud Forms Through Unseen Freezing Process
New models show the Arsia Mons cloud requires a 30-degree temperature drop in ten minutes to create ice without dust particles.
By Aiko Soto ·
A new modeling study explains how a massive cloud forms over the Martian volcano Arsia Mons. The feature, known as the Arsia Mons Elongated Cloud, stretches more than 1,000 miles each morning before vanishing. Researchers say the cloud relies on a physical process never before directly observed in any planet's atmosphere.
The cloud appears during Martian spring and summer. It grows gradually throughout the morning until it reaches a length comparable to the straight-line distance between New York and Kansas City. The cycle repeats for several months before stopping. A probe first recorded the cloud in 2018, leaving scientists without a clear explanation for its formation.
The new work, published in Nature Geoscience, is the first to successfully reproduce the cloud's formation in a computer model. The simulations only worked when researchers included specific conditions described by lead author Jorge Hernández-Bernal as "exotic physics." Hernández-Bernal, a planetary scientist at Sorbonne Université in Paris, noted that while this physics appears in textbooks, it is usually treated as theoretical rather than natural.
"Once we included this physics in our simulations, the AMEC emerged just as we hoped," Hernández-Bernal said in a press release. On Earth, clouds form when water vapor condenses around tiny particles like dust or salt. This study proposes a different mechanism for Mars called homogeneous nucleation. In this process, vapor turns directly into ice crystals without any debris to seed the formation.
The mechanism requires extreme conditions to function. The model shows a temperature drop of 30 degrees Celsius occurring within just ten minutes. High relative humidity is also necessary for the ice to form. Hernández-Bernal compared the process to condensation appearing in the middle of a room rather than on a window, calling the outcome "wholly unexpected."
The volcano Arsia Mons plays a central role in creating these conditions. When wind encounters the 65,000-foot peak, it generates a powerful wave that lifts moist air high into the atmosphere within minutes. This rapid ascent triggers the necessary temperature plunge. Scientists have long assumed similar nucleation could occur in the upper atmospheres of Venus and Earth, but they had never observed it.
The required humidity levels are more than 100,000 times greater than any value measured on Earth. This extreme moisture likely explains why the process has not been seen elsewhere. Researchers did not previously know that such humidity existed on Mars. Hernández-Bernal stated, "The result is remarkable," noting that far less is known about the Martian atmosphere than Earth's.
