Plumes on Europa tease NASA mission planners
A proposed NASA mission to Jupiter's moon Europa is gathering momentum. Congress has long been enthusiastic, and earlier this month the White House finally signed on to the $2 billion mission, which would investigate the habitability of Europa, which might host life in its deep, hidden saltwater ocean. Lately the mission has also gained a tantalizing target: plumes of water vapor that seem to erupt through the moon's icy crust, presumably sweeping any organic molecules into space, where they might be detectable. The trouble is, the plumes might not exist. Observers spotted them with the Hubble Space Telescope in 2012, detecting the fluorescence of oxygen and hydrogen in the water molecules as they were bombarded by electrons whipped up by Jupiter's intense magnetic fields. But dozens of other observational campaigns have failed to spot any plume. That posed a dilemma for the scientists who gathered last week at NASA's Ames Research Center in Mountain View, California, to discuss how the presence of plumes—or their absence—should affect planning for the mission.