Europa's sodium atmosphere: An ocean source?

Sputtering and decomposition of Europa's surface by energetic ions and electrons produce an atmosphere. Here we use a 3D Monte Carlo simulation, including collisions with the background O-2 atmosphere, to describe recent measurements of the sodium component of the atmosphere. By constraining the model with the observational data, we attempt to reconstruct the source processes, the energy distribution, and the flux of the ejected sodium. We confirm that electronic sputtering from ice-rich regions dominates the ejecta and that Europa loses between 5 and 10 x 10(6) Na cm(-2) s(-1). This is about one order of magnitude more sodium than that implanted from the jovian magnetosphere. (C) 2002 Elsevier Science (USA).