Volcanic Origin of Disulfur Monoxide (S2O) on Io

ered sulfur (30%) and sulfur glass (30%) give a better fit to the spectral features than do other candidate materials. We use chemical equilibrium calculations to model S2O forEarlier, Hapke (1989) proposed a mixture of solid S2O mation by high temperature thermochemical reactions in volcanic gases on Io. The calculations predict formation of 1–6% S2O with SO2 frost, polysulfur oxides (SxO)y , and basalt to gas at observed hot spot temperatures in SO2–S2 gas mixtures at explain these spectral features. It is also possible that S3 pressures of 1–100 bars in volcanoes on Io. The S2O abundance and/or S4 formed by partial decomposition of (unstable) increases with increasing pressure (up to p6% at 100 bars) and solid S2O (Schenk and Steudel 1965, 1968, Tang and Brown is relatively insensitive to temperature and the bulk O/S ratio 1975) contribute to the red coloration of S2O frost (Hapke over wide ranges. Condensation of volcanic S2O provides a and Graham 1989). plausible explanation for the solid S2O that has been suggested Sulfur dioxide gas has been observed in a volcanic plume to be present on Io’s surface (e.g., around the Pele volcano). over Loki and over the Pele volcanic region on Io (e.g.,  1998 Academic Press Pearl et al. 1979, Sartoretti et al. 1994, Spencer and Schnei