NaCl & KCl in Io's Atmosphere

TL;DR

This study analyzes NaCl and KCl gases in Io's atmosphere using spectral data from ALMA to infer volcanic activity and magma properties, revealing high temperatures and specific gas ratios indicative of volcanic origins.

Contribution

It provides the first comprehensive spectral analysis of NaCl and KCl in Io's atmosphere, linking gas ratios to magma temperatures and volcanic processes.

Findings

NaCl and KCl gases are spatially confined and hot (~500-1000 K).

NaCl:KCl ratio varies between 3.5 and 6, consistent with volcanic outgassing.

Magma temperature inferred to be around 1300 K based on gas ratios.

Abstract

We present the first comprehensive study of NaCl and KCl gases in Io's atmosphere in order to investigate their characteristics, and to infer properties of Io's volcanoes and subsurface magma chambers. In this work, we compile all past spectral line observations of NaCl and KCl in Io's atmosphere from the Atacama Large Millimeter/submillimeter Array (ALMA) and use atmospheric models to constrain the physical properties of the gases on several dates between 2012 and 2018. NaCl and KCl appear to be largely spatially confined and for observations with high spectral resolution, the temperatures are high (~500-1000 K), implying a volcanic origin. The ratio of NaCl:KCl was found to be ~5-6 in June 2015 and ~3.5-10 in June 2016, which is consistent with predictions based on observations of Io's extended atmosphere, and less than half the Na:K ratio in chondrites. Assuming these gases are volcanic in origin, these ratios imply a magma temperature of ~1300 K, such that the magma will preferentially outgas KCl over NaCl.