FUV emissions on Io: Role of Galileo-observed field-aligned energetic electrons

Abstract

The excitation of Io's atmosphere by Galileo-observed magnetically field-aligned energetic (0.1-100 keV) electrons have been studied using a Monte Carlo model. The calculated OI and SI FUV emissions are compared with HST-STIS observations. It is found that Galileo EPD-observed 15-100 keV electron beams are an insignificant source of OI and SI emissions on Io since they are too energetic to be degraded in Io's atmosphere. We show that Galileo PLS-observed field-aligned 0.1-5 keV electron fluxes can explain the HST-observed S and O FUV brightness provided a fraction of these electrons precipitate into Io's atmosphere. The absorption of FUV emissions by SO2 is found to be less than 10%. From the qualitative scenario of a correlation between Jovian FUV emissions from IFT footprint and Io's FUV emissions we suggest a dual role of field-aligned IFT electrons in producing emissions at Io and Jupiter.