Experimental constraints on the abundance and speciation of darkening agents on the surfaces of the icy Galilean moons — E8 Intelligence Research

The icy Galilean moons, Europa, Ganymede, and Callisto, have surfaces composed of water ice, various salts, sulfuric acid hydrate, and darkening agents. Darkening agents lower overall surface reflectance without imparting strong diagnostic absorption features, making their abundances difficult to constrain. Previous studies estimate darkening agent abundances of <36 wt% for Europa, 20--85 wt% for Ganymede, and 10--100 wt% for Callisto, though these ranges remain highly uncertain. In this study, we seek to understand the possible speciation and abundances of darkening agents on these moons. We prepare mixtures of water ice, sulfuric acid octahydrate (SAO) ice, and graphite or magnetite (two commonly sourced darkening agents) at relevant regolith particle sizes of <45 μm (fine) and 180 to 250 μm (coarse). We compare visible to near infrared (VNIR) reflectance spectra of these ice mixtures to orbital data collected by Galileo's Near-Infrared Mapping Spectrometer (NIMS) instrument to Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com