Paris Researchers Reproduce Daily Martian Cloud Using Theoretical Ice Process
Simulations of the Arsia Mons cloud only matched observations after humidity levels exceeded anything measured on Earth by more than 100,000 times.
By Carolina Wood ·
The humidity required to form a 1,000-mile cloud near a Martian volcano exceeds any value ever recorded on Earth by more than 100,000 times. That figure appears in a new modeling study published in Nature Geoscience, which reproduces the daily formation of the Arsia Mons Elongated Cloud, a feature that grows through the morning and disappears by afternoon during the Martian spring and summer.
The study proposes that the cloud forms through homogeneous nucleation, where water vapor turns directly into ice crystals without dust or salt particles to start the process. Researchers at Sorbonne Université in Paris said their simulations failed to produce the cloud until they added this mechanism. The volcano Arsia Mons stands 65,000 feet tall, and wind passing over it generates a wave that lifts moist air high into the atmosphere within minutes. The required conditions include a temperature drop of 30 degrees Celsius in 10 minutes.
A probe first recorded the feature in 2018. Since then, scientists have not produced a model that matches its behavior. The current work, led by planetary scientist Jorge Hernández-Bernal, is the first to do so.
Hernández-Bernal described the mechanism as "exotic physics" that appears in textbooks but is treated as theoretical and usually considered not to occur in nature. He compared the process to condensation forming in the middle of a room rather than on a window, calling it "wholly unexpected." He said in a press release that once the team included this physics in their simulations, the cloud emerged as expected.
Similar nucleation has been assumed to occur in the upper atmospheres of Venus and Earth, but it has never been observed there. The humidity such a process demands may explain the gap, since the levels required sit far above anything measured on Earth. Researchers also did not previously know that Mars held humidity at those levels. Hernández-Bernal noted that much less is known about the Martian atmosphere than Earth's, and he called the result "remarkable."
The Arsia Mons cloud repeats its morning growth and dissipation cycle over several months each year.
