The Enceladus and OH Tori at Saturn

The remarkable observation that Enceladus, a small icy satellite of Saturn, is actively venting has led to the suggestion that ejected water molecules are the source of the toroidal atmosphere observed at Saturn for over a decade using the Hubble Space Telescope ( HST ). Here we show that the venting leads directly to a new feature, a narrow Enceladus neutral torus. The larger torus, observed using HST , is populated by charge exchange, the process that limits the lifetime of the neutrals in the Enceladus torus.