Water-Group Pickup Ions From Europa-Genic Neutrals Orbiting Jupiter.

Water-group gas continuously escapes from Jupiter's icy moons to form co-orbiting populations of particles or neutral toroidal clouds. These clouds provide insights into their source moons as they reveal loss processes and compositions of their parent bodies, alter local plasma composition, and act as sources and sinks for magnetospheric particles. We report the first observations of H 2 + pickup ions in Jupiter's magnetosphere from 13 to 18 Jovian radii and find a density ratio of H 2 + /H +  = 8 ± 4%, confirming the presence of a neutral H 2 toroidal cloud. Pickup ion densities monotonically decrease radially beyond 13  R J consistent with an advecting Europa-genic toroidal cloud source. From these observations, we derive a total H 2 neutral loss rate from Europa of 1.2 ± 0.7 kg s -1 . This provides the most direct estimate of Europa's H 2 neutral loss rate to date and underscores the importance of both ion composition and neutral toroidal clouds in understanding satellite-magnetosphere interactions.