NASA features an unusual cloud on Mars stretching more than 1,500 kilometres

On November 2, 2026, NASA's Astronomy Picture of the Day highlights an unusually long cloud on Mars. It forms near the volcano Arsia Mons and is known as the Arsia Mons Elongated Cloud (AMEC). The observation shown is archival; the photograph was not taken today.

Ice, not volcanic smoke

The pale streak is a water-ice cloud that forms during spring and summer in the planet's southern hemisphere, mainly in the morning. After it forms, air currents stretch it westward; under certain conditions it extends over 1,500 kilometres, while earlier observations suggest a maximum of around 1,800 kilometres. The cloud usually dissipates within a few hours.

The phenomenon has been photographed by the European Space Agency's Mars Express spacecraft. Researchers have also identified an earlier record dating to 1977 in archives from the Viking 2 mission. Scientists continue to investigate how ice crystals form in Mars's thin atmosphere and how winds produce this unusual shape.

NASA notes that a better understanding of clouds on Mars may also support research into atmospheric processes on Earth. Today's feature revisits a known and studied phenomenon; it is not an announcement of a newly discovered volcanic eruption.

Sources: NASA APOD, November 2, 2026; European Space Agency — image and description.

Photo: ESA/GCP/UPV/EHU Bilbao, CC BY-SA 3.0 IGO (archive image from 2018).