The cloud on Mars that shouldn’t exist — Jorge Hernández-Bernal cracks the red planet’s oddest wisp

Every Martian spring, a white wisp of ice nearly 1,800 km long unfurls from the Arsia Mons volcano each morning, then vanishes by evening. A new peer-reviewed study in Nature Geoscience led by Jorge Hernández-Bernal of the CNRS and Sorbonne finally explains it: winds fling moist air upward so fast that water vapor freezes straight into ice particles with no dust needed — “homogeneous ice nucleation,” long treated as purely theoretical. It is the first time the mechanism has been seen working in nature, and it may shape clouds on distant planets too.