Sulfurous acid (H 2SO 3) on Io?

Abstract

Sulfurous acid (H 2SO 3) has never been characterized or isolated on Earth. This is caused by the unfavorable conditions for H 2SO 3 within Earth's atmosphere due to the high temperatures, the high water content and the oxidizing environment. Kinetic investigations by means of transition state theory showed that the half-life of H 2SO 3 at 300 K is 1 day but at 100 K it is increased to 2.7 billion years. Natural conditions to form H 2SO 3 presumably require cryogenic SO 2 or SO 2/H 2O mixtures and high energy proton irradiation at temperatures around 100 K. Such conditions can be found on the Jupiter moons Io and Europa. Therefore, we calculated IR-spectra of H 2SO 3 which we compared with Galileo's spectra of Io and Europa. From the available data we surmise that H 2SO 3 is present on Io and probably but to a smaller extent on Europa.