Mapping Io's Surface Composition With Juno/JIRAM

Abstract

AbstractThe surface composition of Io is dominated by SO2 frost, plus other chemical species identified or proposed over the past decades by combining Earth‐based and space‐based observations with laboratory data. Here we discuss spectroscopic data sets of Io obtained by the Jovian InfraRed Auroral Mapper (JIRAM) spectro‐imager onboard Juno in nine orbits, spanning a 3‐year period. We display average spectral profiles of Io in the 2–5 μm range, and we use band depths derived from those profiles to map the geographic distribution of SO2 frost and other spectral features. This data set allows for an ~22% surface coverage at 58 to 162 km/px and in a broad range of latitudes. Our results confirm the broadly regional SO2‐frost trends already highlighted by Galileo/NIMS. Io's average spectral profiles as well as the mapping of the 4.47‐μm band also confirm that SO2 exists in the 32S16O18O isotopic form. Surprisingly, the mapping performed by JIRAM shows that the absorption band at 2.1 μm is unrelated to SO2 frost, while we map for the first time the depth of the 2.65‐μm band, highlighting regions enriched in this absorber, possibly H2S. JIRAM data confirm that the 3.92‐μm band, likely due to Cl2SO2, is largely related to the SO2 distribution. The correlation between Cl2SO2 and ClSO2, possibly revealed at 4.62 μm, is not equally clear. The simultaneous presence of two very weak spectral features at 4.55 and 4.62 μm suggests that nitrile compounds or tholins may also be present on the surface.