Observations and Analysis of NaCl and KCl in Io’s Atmosphere

Io’s volcanically-driven atmosphere is controlled by a number of competing processes which affect its density, temperature, and spatial distribution. Trace gases NaCl and KCl in Io’s atmosphere are thought to be the result of volcanic outgassing, but the lack of spatial correlation between these trace gases with Io’s sulfurous volcanic gases open many questions about other possible sources of NaCl and KCl, including sputtering or variations in magma composition.

We present spectral line observations of NaCl and KCl in Io’s atmosphere from the Atacama Large Millimeter Array (ALMA). NaCl and KCl were observed on June 9 and July 26, 2016 in ALMA Band 6 (211-275 GHz), and KCl was observed on March 20, 2018 in ALMA Band 7 (330-348 GHz). By matching the reduced images and line profiles with models of NaCl and KCl spectral line emission, we infer the spatial distribution and constrain the temperature-column density relationship of these trace gases. Variations in these properties will be compared between the different dates, and correlation between the spatial distribution of these gases with that of sulfurous gas emission and a geological map of Io will be assessed. These results will also be compared with ALMA Cycle 1 observations of NaCl and KCl.