Revisiting magnetospheric CAPS TOF data post Cassini

Abstract

The Cassini Plasma Spectrometer has a Time-of-Flight sensor capable of separating out the major magnetospheric ions at Saturn of protons, ions with a mass to charge of 2 amu/q, and water group ions (O+, OH+, H2O+ and H3O+), yet until this study a survey of their relative proportions in density with respect to radial distance has not been carried out. Most past work had used a standard code for the Time-of-Flight analysis, however we find that this code had a few features that resulted in it underestimating the relative proportion of water group ions and overestimating those of the light ions, which has consequences for past studies that relied on this code. Those features are addressed in this study to find that the water group ions dominate the equatorial magnetosphere out to ≈40RS, further than previously assumed. The ions of mass to charge 2 amu/q (assumed to be H2+) are the third most abundant ion group (after protons and the water group), with less than 12% of the total ion density. In addition, the presence of an H2+ distribution is found that appears to have Titan as the source, since H2+ ions can dominate the near Titan environment.