Soft X-Ray Emission from Saturn's Magnetosheath II : Solar Wind Driving

Saturn's magnetosphere is dominated by Enceladus-sourced neutrals, which spread throughout the system into the magnetosheath. The neutrals can charge exchange with highly charged solar wind ions, causing soft X-ray emission (<2 keV) upon de-excitation of the ion. Imaging these soft X-rays can reveal the global, dynamic structure of the magnetosheath and cusps of a magnetosphere and give insight into the complex nature of the solar wind interaction with the planet. A model of soft X-ray emission from Saturn's magnetosheath is presented, considering charge exchange between Enceladus-sourced neutrals and highly charged oxygen ions (O7+ and O8+). We estimate emission rates and the flux that would be detected by a SMILE-like soft X-ray imager (SXI). Solar wind dynamic pressure is varied to test the effect of solar wind conditions on X-ray production. Volumetric emission rate is on the order of 10-11 and 10-10 photon cm-3 s-1 for slow and fast solar winds, respectively. A compressed magnetosphere has higher neutral density in the magnetosheath leading to more emission. For a SMILE-like SXI imaging at at a distance of 53 RS, we estimate over a hundred photons can be detected within a quarter of a planetary rotation. A `future' SXI, with double the FOV of SMILE's and 100 cm2 effective area, significantly improves integration times, reducing integration time to~2.5 s when imaging at 25 RS. Under a point source approximation, the modelled SXIs perform well to large distances, with Earth-based observations potentially being possible with an XMM-Newton-like instrument.