Once again we take advantage of older databanks to tease out new information. Europa is the case in point this morning, with Galileo data — magnetic field and plasma wave observations from 1997 — being brought in as evidence for a water vapor plume rising from the surface. The Galileo flyby took the craft closer than 400 kilometers, where a brief spike in plasma density was detected along with a concurrent decrease in magnetic field magnitude and a bend in the direction of the field. The data are consistent with a plume interacting with Jupiter’s plasma outflow, and support earlier Hubble indications of possible plumes on the moon.
We have no firm measurement of the thickness of Europa’s ice, but if we are to get to that fascinating ocean now known to exist below the surface, we have to contend with penetrating it. Plumes from the interior would be helpful indeed, as Enceladus showed us at Saturn. Flying a spacecraft through a plume lets us measure its ingredients and sample the ocean below. So this new work, which has just been published in Nature Astronomy, offers the prospect of plume sampling via close flyby for upcoming missions like Europa Clipper.