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Enceladus has a dynamic plume that is emitting gas, including water vapor, and dust. The gas is ionized by solar EUV radiation, charge exchange, and electron impact and extends throughout the inner magnetosphere of Saturn. The charge exchange collisions alter the plasma composition. Ice grains (dust) escape from the vicinity of Enceladus and form the E ring, including a portion that is negatively charged by the local plasma. The inner magnetosphere within 10 R S (Saturn radii) contains a complex mixture of plasma, neutral gas, and dust that links back to Enceladus. In this paper we investigate the energy distributions, ion species and densities of water group ions in the plume of Enceladus using test particle and Monte Carlo methods that include collisional processes such as charge exchange and ion-neutral chemical reactions. Ion observations from the Cassini Ion and Neutral Mass Spectrometer (INMS) for E07 are presented for the first time. We use the modeling results to interpret observations made by the Cassini Plasma Spectrometer (CAPS) and the INMS. The low energy ions, as observed by CAPS, appear to be affected by a vertical electric field ( E Z =−10 µV/m) in the plume. The E Z field may be associated with the charged dust and/or the pressure gradient of plasma. The model results, along with the results of earlier models, show that H 3 O + ions created by chemistry are predominant in the plume, which agrees with INMS and CAPS data, but the INMS count rate in the plume for the model is several times greater than the data, which we do not fully understand. This composition and the total ion count found in the plume agree with INMS and CAPS data. On the other hand, the Cassini Langmuir Probe measured a maximum plume ion density more than 30,000 cm −3 , which is far larger than the maximum ion density from our model, 900 cm −3 . The model results also demonstrate that most of the ions in the plume are from the external magnetospheric flow and are not generated by local ionization. The origin of the ions in the plume was investigated using two different velocity models. Most ions were created by the interaction with background magnetospheric plasma and by photoionization. INMS and CAPS also detected water cluster ions. We will interpret these observations as a result of ion collisions with neutral water clusters, (H 2 O) n , originating in the tiger stripe vents as suggested by Tokar et al. (2009). We also estimated the process of generating cluster ions based on the INMS observations. We suggest that the most likely source is reaction of H 3 O + with neutral water clusters or dimers such as (H 2 O) 2 formed in the plume vents. [ABSTRACT FROM AUTHOR]

While Saturn's largest moon Titan is devoid of an intrinsic magnetic field, draping of the giant planet's magnetospheric field around Titan's ionosphere generates a pile-up region at the moon's ramside. In this study, we analyze Cassini magnetic field data from all 126 Titan flybys to systematically characterize the extensions and magnitudes of the field enhancements at its ramside. Along each flyby trajectory, the segments where Cassini crossed the piled-up magnetic field are determined, and altitude profiles of the pile-up strength are also generated. We investigate the dependency of the extension and strength of the pile-up region on various parameters, such as the Saturn local time and the magnetospheric environment to which Titan is exposed. In this way, we generate a comprehensive picture of Titan's ramside magnetic pile-up region during the Cassini era. Our major findings are: (1) The extensions of the observed pile-up reveal an asymmetry between the Saturn-facing and Saturn-averted sides caused by the large gyro-radii of ionospheric pick-up ions. (2) The observed pile-up radial extensions are nearly independent of Titan's orbital position. (3) The lower boundary of the pile-up region is located at an altitude of 0.35 Titan radius, denoting the average altitude of the magnetic ionopause. (4) Considering the error bars, the altitude profiles of the pile-up strength show a stable picture, i.e., the radial profile of the field magnitude is independent of Saturn's magnetospheric environment and local time. • Extensions of the observed pile-up reveal an asymmetry between the Saturn-facing and Saturn-averted sides. • Observed pile-up radial extensions are nearly independent of Titan's orbital position. • Lower boundary of the pile-up region is located at an altitude of 0.35 Titan radii. • Altitude profiles of the pile-up strength are independent of Saturn's magnetospheric environment and local time. [ABSTRACT FROM AUTHOR]