Mars' 1,000-Mile Morning Cloud Requires 100,000 Times Earth's Humidity
A new model shows the cloud forms through a rare freezing process that has never been directly observed in any planetary atmosphere.
By Katherine Barnes ·
A narrow band of ice that stretches more than 1,000 miles across the Martian surface each morning likely forms through a physical process that scientists have never directly observed in any planet's atmosphere. The finding, published in Nature Geoscience, offers the first successful model for the Arsia Mons Elongated Cloud, a feature that has puzzled researchers since a probe first captured it in 2018.
The cloud appears during Martian spring and summer, growing steadily longer until it reaches a span comparable to the straight-line distance from New York to Kansas City. It then dissipates, with the cycle repeating over several months. For years, scientists struggled to explain how such a vast feature could form and vanish so predictably.
The breakthrough came when researchers at Sorbonne Université in Paris incorporated what lead author Jorge Hernández-Bernal described as "exotic physics" into their simulations. This mechanism, known as homogeneous nucleation, allows water vapor to turn directly into ice crystals without settling onto dust or salt particles. On Earth, clouds typically form when vapor condenses around debris. Hernández-Bernal compared the Martian process to droplets of condensation appearing in the middle of a room rather than on a window.
The model required extreme conditions to work. The simulations showed that air must cool by 30 degrees Celsius within just 10 minutes. The volcano Arsia Mons, which stands 65,000 feet high, plays a central role in creating these conditions. When wind strikes the mountain, it generates a powerful wave that lifts moist air high into the atmosphere rapidly.
The process demands humidity levels that are more than 100,000 times greater than any value measured on Earth. Scientists had not previously known such humidity existed on Mars. While similar nucleation was assumed to occur in the upper atmospheres of Venus and Earth, it has never been confirmed. Hernández-Bernal noted that the Martian atmosphere remains less understood than Earth's, making the successful reproduction of the cloud a notable achievement.
The study suggests that the cloud's formation is not a mystery but a specific, albeit rare, interaction between the volcano's topography and the planet's atmospheric moisture. The model now provides a baseline for understanding how such extreme weather events function on Mars.
Source: Wired
