Mars Cloud Mystery Solved: Exotic Ice Physics Creates 1,000-Mile Storm
A new model reveals that the Arsia Mons Elongated Cloud forms through a rare ice process that demands conditions never previously recorded on any planet.
By Harper Hassan ·
The wispy cloud that stretches across more than 1,000 miles near the Martian volcano Arsia Mons every morning likely forms through a physical process never directly observed in a planetary atmosphere. A new modeling study published in Nature Geoscience successfully reproduces the cloud's daily cycle, offering the first plausible explanation for a phenomenon that has puzzled scientists since its discovery.
Known as the Arsia Mons Elongated Cloud, or AMEC, this feature appears during the Martian spring and summer. It grows longer through the morning until it reaches a size comparable to the straight-line distance between New York and Kansas City, then dissipates. This cycle repeats over several months. A space probe first recorded the cloud in 2018, but researchers have struggled to explain its existence without relying on standard cloud formation theories.
Lead author Jorge Hernández-Bernal, a planetary scientist at Sorbonne Université in Paris, stated that the simulations only succeeded when they included what he described as exotic physics. This process, known as homogeneous nucleation, involves water vapor turning directly into ice crystals without any dust or salt particles to seed the formation. Hernández-Bernal compared it to droplets of condensation appearing in the middle of a room rather than on a window. He noted that while the physics appears in textbooks, it is usually treated as theoretical and unlikely to occur in nature. Once the team added this mechanism to their models, the AMEC emerged exactly as observed.
The process requires extreme conditions to function. The model shows that the cloud forms when wind hits the 65,000-foot Arsia Mons, generating a powerful wave that lifts moist air high into the atmosphere within minutes. This rapid ascent causes a temperature drop of 30 degrees Celsius in just 10 minutes. The environment must also sustain high relative humidity, a factor that explains why the cloud was not previously detected in other planetary atmospheres like Venus or Earth.
The humidity levels required for this nucleation process are more than 100,000 times greater than any value measured on Earth. Scientists had not previously known that such humidity existed on Mars. Hernández-Bernal emphasized that far less is known about the Martian atmosphere than about Earth's, making the ability to reproduce the cloud's specific behavior a major step forward in understanding the planet's weather systems.
The findings suggest that similar nucleation processes may occur in the upper atmospheres of other planets, though they have yet to be observed. The study indicates that the Arsia Mons volcano is central to creating the necessary conditions for the cloud's daily formation. The research, originally reported by Wired Czech Republic and Slovakia, provides a concrete mechanism for a feature that has defied explanation for years.
Source: Wired
