Researchers model formation of a cloud more than 1,000 miles long on Mars — Ars Technica

Researchers have for the first time modeled the formation of an elongated cloud near the Martian volcano Arsia Mons. The model indicates that the structure, which stretches for more than 1,000 miles and later dissipates, may form due to a physical process that has not yet been directly observed in the atmosphere of any planet, Ars Technica reports.

The cloud appears in the morning

The thin cloud, known as the Arsia Mons Elongated Cloud, or AMEC, appears every morning during spring and summer on Mars. It forms near the volcano, gradually stretches into a long plume, and then dissipates. This cycle repeats for several months.

Such a cloud was first recorded by a probe in 2018. The 65,000-foot-high Arsia Mons volcano plays a key role in the model: when an airflow encounters it, a powerful wave forms, lifting moist air high into the atmosphere within minutes.

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Ice crystals without dust

On Earth, clouds usually form when water vapor creates droplets or ice crystals in the presence of small particles, including dust or salt. The authors of the study, published in Nature Geoscience, suggest that a different mechanism operates for AMEC: homogeneous nucleation. Under this mechanism, vapor turns into ice crystals without foreign particles.

Such a process requires extreme conditions: the temperature must drop sharply by 30 degrees Celsius within 10 minutes, while relative humidity must be very high. The scientists note that the required humidity level is more than 100,000 times higher than any values measured on Earth. Before this model was created, it was not known that similar conditions could exist in Mars' atmosphere.