Presentation #103.02 in the session Unmeltable Me, verse 1: From the Sky to the Lab.
The ancient surface of Jupiter’s moon Callisto is one of the key records of long-term bombardment in the Solar System. Bearing little to no evidence for geologic activity or any discernible surface-interior interactions, Callisto has done little more than collect and degrade its impact features for the past 4.5 billion years. Such features range from simple craters to the enormous multi-ring impact basin Valhalla (D ~ 3800 km). At present, our knowledgebase of Callisto’s material surface properties is limited compared to this satellite’s Galilean siblings At thermal mm wavelengths, high resolution maps have been obtained for the other icy Galilean moons, and such maps were useful for probing the physical properties (e.g, thermal inertia, emissivity) of their surfaces at depth (Europa: Trumbo+2017, 2018; Ganymede: de Kleer+ 2021). Understanding the distribution of the physical properties across a planetary surface can illuminate both the interior and evolution of a planetary body. Here, we present a thermal image of Callisto’s leading hemisphere obtained at 345 GHz with ~790 km spatial resolution using the Atacama Large Millimeter/submillimeter Array (ALMA). We model these data using a thermal model (de Kleer+ 2021) constrained by spacecraft data to obtain global surface properties (e.g., thermal inertia and emissivity). We will present our best-fit global models, and will discuss both thermal anomalies that might correspond to known geologic features (e.g., large impact basins) and systematic patterns of thermal anomalies unaccounted for by the model. These results are part of a suite of observations we acquired to make 1) the first global thermal map of Callisto, and 2) the highest-resolution millimeter maps of its surface to date.