A 1,800 km Cloud Wakes Up on Mars Every Morning Every Martian spring and summer, something extraordinary happens on the Red Planet.Just before sunrise, a gigantic ribbon of cloud awakens on the leeward side of Arsia Mons — a colossal, extinct volcano that still towers 20 km above the Martian surface. In just two and a half hours, this cloud explodes in size: stretching 1,800 km long and 150 km wide, racing westward at over 600 km/h — faster than a jet airliner. It becomes the largest orographic cloud ever recorded on Mars, so massive it can be seen from Earth through a telescope.Then, as the Sun climbs higher and warms the atmosphere, the entire cloud detaches, drifts away… and completely evaporates before noon.This is AMEC — the Arsia Mons Elongated Cloud — a breathtaking daily performance of Martian weather, not a volcanic eruption. It’s made of water-ice crystals condensing at an altitude of 45 km as cold air is forced up the volcano’s slopes.The cycle is incredibly reliable. It repeats like clockwork for more than 80 Martian days (sols) every spring and summer.We’ve been watching it for nearly 50 years:NASA’s Viking 2 caught the first blurry hints in the 1970s.
Today, MAVEN, Mars Reconnaissance Orbiter, and Mars Odyssey study its chemistry and winds.
On May 2, 2025, Mars Odyssey captured the first-ever clear view of the volcano’s peak poking through the dawn cloud tops.
ESA’s Mars Express has delivered stunning time-lapse footage showing the full dramatic “birth and disappearance” of this cosmic ribbon.
A dead volcano on Mars is still creating one of the most spectacular weather phenomena in the Solar System — every single morning. Nature never stops surprising us.