The rounded head and tapered tail of the Arsia Mons Elongated Cloud drifts west from its namesake volcano in this view from Mars Express’ High Resolution Stereo Camera, captured June 24, 2024. New simulations suggest the cloud forms through homogeneous nucleation, as ice crystals freeze directly out of water vapor rather than around particles of dust, a process never before seen in a planetary atmosphere. Credit: ESA/DLR/FU Berlin

Scientists believe they may finally have an explanation for a bizarre cloud that appears and promptly disappears each day above a martian volcano during the dusty season.

Just after sunrise during spring and summer on Mars, an elongated cloud forms near the 12-mile-high (20 kilometers) volcano Arsia Mons. Stretching roughly 1,100 miles (1,800 km) in length, the aptly named Arsia Mons Elongated Cloud (AMEC) is unlike any cloud previously observed on the Red Planet.…