Modeling the Loss of Neutral Material From Io

Abstract:

While Io has been known since the 1970s to produce clouds of neutral material (S, O, and Na atoms) that stretch around its orbit, the actual processes causing the ejection of these neutrals are poorly understood.
The canonical rate of 1 ton per second of neutral loss is largely based on what is needed to feed these atomic neutral clouds as well as feed the Io plasma torus (via electron impact ionization of the neutrals).

We note that reactions with molecular species from Io’s atmosphere need to be included.

We estimate Io’s SO2 neutral loss from two important mechanisms: (1) resonant charge exchange of SO2+ ions in the atmosphere and corona of Io; and (2) the dissociative recombination of SO2+ ions in Io’s dense wake.

To estimate Io’s loss rate we combine an MHD simulation of the plasma flow around Io with a multi-species chemistry simulation of the ion-neutral reactions in an SO2 atmosphere.