Discovery of chlorine in the Io torus

Abstract

We report the discovery of singly ionized chlorine in the Io plasma torus through the detection of emission at 857.9 nm. The 40 Rayleigh peak intensity at 857.9 nm corresponds to a Cl+ abundance of 2±0.5% relative to all ions. Since Cl+ probably originates at Io, Io's atmosphere must have the highest proportion of chlorine of any solar system body. While Cl+ plays only a minor role in torus physics, the presence of chlorine in Io's atmosphere, surface, and interior has more profound implications. Salt as a solid or gas is probably an important source of both Na and Cl in Io's vicinity.