Rare Suprathermal Heavy Ions in Saturn's Magnetosphere

The Cassini/MIMI/CHEMS ion spectrometer has measured suprathermal (~83-167 keV/e) ions in Saturn's magnetosphere since mid-2004. We report on three rare, heavy ion groups measured in Saturn's ~4-20 Rs magnetosphere at ~40, ~46, and ~56 amu/e, with the separation from other species best at higher mass. These masses suggest possible singly-charged ion identifications as Ar⁺, CO₂⁺, and Fe⁺, respectively. The presence of these species or compounds containing them has been suggested in composition studies of Saturn's particle populations using data from other instruments on Cassini. The observed rare ion intensities are highly variable in time and space. Broad temporal and spatial averaging is needed to examine these rare ion groups because their detection levels are much lower than the dominant water ion group, W⁺ (which includes O⁺, OH⁺, H₂O⁺, and H₃O⁺). W⁺ itself can be quite variable. We show that these rare ions display unique spatial and temporal variations, with similarities and differences from the dominant ion group W⁺ as well as O₂⁺ and M28⁺, all local origin ions. We compare and contrast these rare, heavy ion species to W⁺ and the recently characterized [Christon et al., 2013, 10.1002/jgra.50383] minor ions M28⁺ (C₂H₅⁺, HCNH⁺, N₂⁺, and/or CO⁺) and O₂⁺ (M32⁺).