Longitude dependences of energetic H+ and O+ at Saturn

Abstract

The charge‐energy‐mass spectrometer instrument in the Cassini spacecraft measured differential fluxes of protons (2.8–236 keV) and oxygen ions (8.8–236 keV) from July 2004 to August 2007. The fluxes were bin‐averaged in Saturn longitude system (SLS) longitude within ±5 RS of the equator and between 8 and 12 RS in radial distance (1 RS = 60,238 km) to determine their global morphology. The 3‐year time period is the range of validity of the SLS, which is based on a variable period of Saturn kilometric radiation. Fluxes at all energies of H+ and O+ display an essentially sinusoidal variation in longitude, often with peak‐to‐trough ratios of 2:1. For E < 77 keV, the maxima are consistently at ∼70° longitude (the minima are at ∼230°). For E > 77 keV; the maxima shift to ∼250°. The ion distributions closely resemble those of energetic neutral hydrogen and neutral oxygen atoms observed by the ion neutral camera onboard Cassini.