Global Neutral gas Distribution at Saturn and Jupiter Derived From ENA Images

Neutral gas distributions around giant planets are important indicators of the source, loss and transport processes that redistribute material from the planet, its moons and rings, through interaction with the ambient plasma of the magnetosphere. Energetic Neutral Atoms (ENAs) are produced by charge exchange between energetic ions and neutral gas and can be imaged by the INCA camera on board Cassini providing a marker for plasma-neutral processes. As Cassini flew by Jupiter Cassini-INCA data was used to reveal a trans- Europa gas torus [Mauk et al., Nature, 2003]. We demonstrate a technique to retrieve the global neutral gas distribution in Saturn's magnetosphere using ENA images obtained from the INCA imager on board Cassini. The neutral gas distribution at Saturn is retrieved by simulating INCA images using ion distributions of combined CHEMS, LEMMS and INCA in-situ ion measurements that cover several passes from the SOI (183/2004) to day 100/2007, at various local times over the dipole L range 5