Mars Mystery Solved: Scientists Pinpoint Cause of 'Impossible' Daily Cloud
A unique atmospheric phenomenon driven by exotic physics creates a massive cloud near a Martian volcano, baffling scientists until now.
Scientists have resolved a long-standing enigma on Mars: the daily formation and disappearance of an enormous cloud near the Arsia Mons volcano. This cloud, known as the Arsia Mons Elongated Cloud (AMEC), forms each day during the spring and autumn on Mars, extending an astonishing 1,120 miles (1,800 kilometers) downwind from the 12.5-mile-tall volcano.
The phenomenon, first observed in 2018, has puzzled researchers due to its regular appearance and rapid dissipation. Unlike typical cloud formation on Earth, which relies on atmospheric particles like dust for water vapor to condense around, the AMEC appears to form through a process termed "homogeneous nucleation."
This 'exotic' physics, as described by lead author Dr. Jorge Hernández-Bernal of Sorbonne University, involves water vapor directly transforming into ice particles without any intermediate step. "It’s akin to droplets of condensation appearing in the middle of a room, rather than on a window," Hernández-Bernal explained. "We call this homogeneous nucleation, and we’ve never seen it before in a planetary atmosphere. It’s wholly unexpected."
Previous attempts to model the AMEC in computer simulations failed to replicate the observed phenomenon. Scientists understood Mars's atmospheric processes but found the AMEC's behavior defied conventional explanations. For instance, the cloud's formation at high altitudes suggested it wasn't a result of water transport from the surface, and temperature variations alone didn't fully account for its daily cycle.
The key to solving the mystery, according to research published in Nature Geoscience, lies in the unique environmental conditions created by Arsia Mons. The volcano's immense height and Mars's thin atmosphere interact with prevailing winds to create a powerful wave. This wave rapidly lifts moist air parcels high into the atmosphere, causing a dramatic temperature drop of approximately 30°C (54°F) within minutes and a significant spike in relative humidity.
These extreme conditions, requiring humidity levels far exceeding those commonly found on Earth, create the precise environment needed for homogeneous nucleation to occur. "In our daily lives it is uncommon to have relative humidities higher than 100 per cent, but we need around 100,000 times that for homogeneous nucleation to occur," Hernández-Bernal noted.
When this homogeneous nucleation process was incorporated into simulations, the models began producing results that closely matched the observed AMEC. "Even though some details of the model don't exactly match the real cloud, the researchers say that the results are 'remarkable'," the study authors stated.
The discovery suggests that Mars's atmosphere may be capable of reaching extreme humidity levels previously unobserved, potentially indicating that the Red Planet is a more dynamic and complex environment than previously understood. The research was based on observations made by the European Space Agency’s Mars Express orbiter.
