Model explains Mars cloud mystery
Sorbonne researchers used extreme humidity levels to replicate the Arsia Mons cloud in a computer simulation.
By Thiago Kovalenko ·
Scientists have long puzzled over a specific weather pattern on Mars that defies standard atmospheric models. A new study published in Nature Geoscience offers a physical explanation for this phenomenon.
The feature, known as the Arsia Mons Elongated Cloud or AMEC, appears every morning during the Martian spring and summer. It stretches across more than 1,000 miles, a distance comparable to the straight-line span between New York and Kansas City. The cloud grows gradually until it dissipates later in the day. This cycle repeats over several months.
A probe first detected the cloud in 2018. Researchers previously struggled to explain its formation using standard cloud physics. The new modeling work represents the first successful replication of the cloud in a simulation.
Jorge Hernández-Bernal, a planetary scientist at Sorbonne Université in Paris, led the study. He stated that the simulations only worked when the team included what he described as exotic physics. This process appears in textbooks but is usually treated as theoretical. Hernández-Bernal said in a press release that once the team included this physics, the cloud emerged as hoped.
The model proposes that the cloud forms through homogeneous nucleation. In this process, vapor turns directly into ice crystals without dust or salt particles to seed the formation. On Earth, clouds typically form when water vapor condenses around tiny debris. Hernández-Bernal compared the Martian process to droplets appearing in the middle of a room rather than on a window. He called the finding wholly unexpected.
The formation requires extreme conditions. The model shows a temperature drop of 30 degrees Celsius within 10 minutes. It also requires high relative humidity. The 65,000-foot Arsia Mons volcano plays a central role. When wind hits the volcano, it creates a wave that lifts moist air into the atmosphere quickly. The humidity levels needed are more than 100,000 times greater than any value measured on Earth.
Researchers did not previously know that such humidity existed on Mars. The study suggests that similar nucleation could occur in the upper atmospheres of Venus and Earth, though it has never been observed there. Hernández-Bernal noted that far less is known about the Martian atmosphere than Earth's. He described the result as remarkable.
