Where does Mercurys atmosphere come from?
Mercury’s incredibly tenuous atmosphere is unstable, with gases regularly escaping the planet’s weak gravity. How Mercury’s atmosphere gets constantly replenished is unclear. Researchers suspect the hydrogen and helium in Mercury’s atmosphere is continuously brought there by the solar wind, the supersonic stream of charged particles from the sun. Other gases might have evaporated off Mercury’s surface, seeped from inside the planet or been brought in by vaporized meteorites. MESSENGER will closely study the planet’s atmosphere to pinpoint how it gets generated, Vilas said. Why is Mercury magnetic? A completely unexpected discovery Mariner 10 made was that Mercury possessed a magnetic field. Planets theoretically generate magnetic fields only if they spin quickly and possess a molten core. But Mercury takes 59 days to rotate and is so small — just roughly one-third Earth’s size — that its core should have cooled off long ago. To solve this mystery, MESSENGER will probe Mercury’s magneti
