The extended Saturnian neutral cloud as revealed by global ENA simulations using Cassini/MIMI measurements

We show that the neutral gas vertical distribution at Saturn must be similar to 3-4 times more extended than previously thought for the >5R(S)regions, while the neutral Hdistribution is consistent with Hdensities that reach up to similar to 150/cm(3)close to the orbit of Titan. We utilize a technique to retrieve the global neutral gas distribution in Saturn's magnetosphere, using energetic ion and energetic neutral atom (ENA) measurements, obtained by the Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft. Our ENA measurements are consistent with a neutral cloud that consists of H2O, OH, H, and O, while the overall shapes and densities numbers concerning the neutral gas distributions are constrained according to already existing models as well as recent observations. The neutral gas distribution at Saturn is determined by simulating a 24-55keV hydrogen image of the Saturnian magnetosphere, measured by the Ion and Neutral Camera (INCA), averaged over the time period from 1July 2004 to 23 August 2005. The ionic input of the model includes a proton distribution of combined Charge Energy Mass Spectrometer (CHEMS, 3-230keV/e), Low Energy Magnetospheric Measurements System (LEMMS, 30.7keV to 2.3MeV), and INCA (5-300keV) in situ measurements. These measurements cover several passes from 1July 2004 to 10April 2007, at various local times over the dipole Lrange 5<20R(S). A parameterized neutral gas distribution is changed until agreement between the simulated and average INCA image is obtained.