Mars grows an 1,800-km cloud every morning, and it may form in a way never seen on any planet

Every morning on Mars, a water-ice cloud up to 1,800 km long, nearly twice the length of Britain, unfurls off the Arsia Mons volcano and fades by noon. A new study finds the only way to reproduce it is with “exotic physics”: water freezing straight out of vapor without dust, a process never seen in any planet’s atmosphere. A look at what’s measured and what’s inferred.