The Neutral Water Torus of Europa

Abstract

Abstract The neutral particles that escape Europa form a neutral torus which asymmetrically encircles the giant planet Jupiter. The study of this structure can inform on neutral escape at the icy moon and on the loading of the Jovian magnetosphere with Europan material. In this letter, we present the first Monte Carlo model of the neutral water torus of Europa. Water molecules are released to high altitude by ion sputtering of the surface and get dissociated and ionized mostly by electron impact. We find that the density of H2O molecules can be as large as atomic O in a large region of the Jovian magnetosphere. The neutral torus of Europa may therefore have a more diverse composition than previously thought. Plasma instrumentation able to separate H2O+ from O+ pick‐up ions could help to advance our understanding of the neutral torus of Europa.