Sulfurous acid (H2SO3) on Io?

Sulfurous acid (H2SO3) has never been characterized or isolated on Earth. This is caused by the unfavorable conditions for H2SO3 within Earthʹs 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 H2SO3 at 300 K is 1 day but at 100 K it is increased to 2.7 billion years. Natural conditions to form H2SO3 presumably require cryogenic SO2 or SO2/H2O 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 H2SO3 which we compared with Galileoʹs spectra of Io and Europa. From the available data we surmise that H2SO3 is present on Io and probably but to a smaller extent on Europa.