Model traces Mars's 1,000-mile cloud to unobserved ice physics
Simulations attribute the Arsia Mons Elongated Cloud's formation to homogeneous nucleation, an ice-forming process never directly observed in nature.
The story in focus
Researchers report the first successful modeling of the Arsia Mons Elongated Cloud on Mars, according to Ars Technica. Their simulations required homogeneous nucleation, in which vapor freezes directly into ice crystals without seed particles, driven by rapid cooling and high humidity as wind strikes the volcano.
- The first modeled formation of the Arsia Mons Elongated Cloud was published in Nature Geoscience.
- The cloud stretches more than 1,000 miles and recurs each Martian spring and summer morning.
- Reproducing it required homogeneous nucleation, treated as theoretical and not previously observed in nature.
- Formation conditions include a 30°C temperature drop within 10 minutes and humidity over 100,000 times any value measured on Earth.
- Wind striking the 65,000-foot Arsia Mons volcano launches moist air high into the atmosphere in minutes.
An unexplained cloud, modeled at last
Since a probe first recorded it in 2018, researchers had no plausible explanation for the Arsia Mons Elongated Cloud. Every Martian spring and summer morning, the thin formation emerges near the volcano, lengthens past 1,000 miles, and dissipates, repeating for several months.
A team led by Jorge Hernández-Bernal, a planetary scientist at Paris's Sorbonne Université, modeled its formation for the first time, with results published in Nature Geoscience. Ars Technica reports the simulations reproduced the cloud once the researchers added the needed physics.
Freezing without seeds
Earth clouds typically form when water vapor condenses into droplets or ice crystals around particles such as dust or salt. The simulations instead point to homogeneous nucleation, in which vapor turns directly into ice crystals without debris. Hernández-Bernal called the process akin to condensation appearing in the middle of a room rather than on a window.
The process demands extreme conditions: a 30°C temperature drop within ten minutes and relative humidity more than 100,000 times any value measured on Earth. Wind hitting the 65,000-foot Arsia Mons volcano generates a powerful wave that lifts moist air high into the atmosphere in minutes. Before this modeling, such humidity levels were not known to exist on Mars.
What comes next
Homogeneous nucleation has been assumed possible in the upper atmospheres of other planets, including Venus and Earth, but never observed. The study's authors describe reproducing the cloud as a major success given how little is known about Mars's atmosphere compared with Earth's.
What process do the new simulations suggest forms the Arsia Mons Elongated Cloud?
Homogeneous nucleation, in which vapor freezes directly into ice crystals without seed particles. Ars Technica reports the process is treated as theoretical and has not been observed in nature.
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