Mars Cloud Model Relies on Unseen Freezing Process
A new simulation reproduces the Arsia Mons cloud by assuming water vapor freezes into ice without dust seeds, a condition requiring humidity levels 100,000 times higher than Earth's.
By Elijah Fitzgerald ·
A daily weather pattern on Mars that has puzzled researchers for years may depend on a physical process never directly witnessed in a planet's atmosphere. The phenomenon involves a narrow cloud stretching over 1,000 miles near the Arsia Mons volcano. A new modeling study offers the first successful reproduction of this feature, suggesting it forms through homogeneous nucleation.
The Arsia Mons Elongated Cloud appears during the Martian spring and summer. It grows longer throughout the morning until it spans a distance comparable to the straight line between New York and Kansas City, then dissipates. This cycle repeats over several months. A probe first recorded the cloud in 2018, but scientists have struggled to explain its formation until now.
Jorge Hernández-Bernal, a planetary scientist at Sorbonne Université in Paris, leads the study published in Nature Geoscience. He stated that the simulations only worked after including what he called "exotic physics." This physics appears in textbooks but 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. The Martian model proposes a different mechanism. Vapor turns directly into ice crystals without any debris to seed the process. Hernández-Bernal compared this to condensation appearing in the middle of a room instead of on a window, calling it "wholly unexpected."
The process requires extreme conditions. Temperatures must drop 30 degrees Celsius within 10 minutes, and relative humidity must be very high. The Arsia Mons volcano, which stands 65,000 feet high, plays a central role. When wind hits the volcano, it creates a powerful wave that lifts moist air high into the atmosphere within minutes.
The humidity levels required are more than 100,000 times greater than any value measured on Earth. Scientists previously did not know such humidity existed on Mars. Hernández-Bernal noted that far less is known about the Martian atmosphere than Earth's. "The result is remarkable," he said.
