Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p33a1566w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P33A-1566
Physics
[2732] Magnetospheric Physics / Magnetosphere Interactions With Satellites And Rings, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites
Scientific paper
Enceladus, orbiting at 3.95 Saturn radii, is the primary mass-loading source for the neutral cloud in the inner magnetosphere. Cassini observations have revealed that the Enceladus‘ southern plume releases hundreds of kilograms of water-group neutrals per second. Ionization of these neutrals generates pickup ions which have unstable pitch angle distributions in velocity space and create electromagnetic ion cyclotron waves. These waves can be studied as diagnostic tools for the mass-loading process because the wave amplitude is proportional to the ionization rate of the newly added mass. The ion cyclotron waves are observed throughout the extended neutral cloud, from slightly inside Enceladus‘ orbit to outside of Dione’s. At the Enceladus orbit, the waves are longitudinally asymmetric, enhanced between forty degrees upstream and over a hundred degrees downstream of the moon’s position. These observations are used to estimate the ionization rate of the neutral cloud and the ion production rate from Enceladus fast neutrals. We use a Monte Carlo particle-tracing code to simulate the pickup ions and fast neutrals produced by Enceladus. This model assumes the neutral gas produced from Enceladus is first ionized, accelerated by the corotational electric field and then drifts away from the source region. Later, it is neutralized by charge exchange and are transported across field lines as fast neutrals, which may be re-ionized or may escape the Saturnian system. The model shows that the pickup ions, which generate ion cyclotron waves, extend far from Enceladus both upstream and downstream, consistant with the wave observations. The fast neutrals also travel largely outward from the Enceladus orbit and could escape the Saturnian system. Furthermore, we compare the wave observations during each Enceladus pass with the model predictions to investigate the plume geometry, the initial velocity of particles in the plume, and variability of the ion production rate.
Cowee Misa M.
Dougherty K. M. K. M.
Jia Yu
Leisner Jared S.
Russell Christopher T.
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