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Thermal Properties of Europa’s Leading and Trailing Sub-surface

Presentation #504.05 in the session Galilean Satellites: Scratching the Surface (Oral Presentation)

Published onOct 23, 2023
Thermal Properties of Europa’s Leading and Trailing Sub-surface

Previous measurements by spacecraft and Earth-based facilities have revealed the surface of Europa to be relatively young and active, with several identified terrain units, a dearth of craters, and hemispherically-asymmetric coloration and composition. The asymmetries may arise from exogenous weathering from the Ionian plasma torus and Jovian radiation environment and/or from endogenic alteration from Europa’s sub-surface ocean. The structure, composition, and evolution of the regolith shed light on the surface modification processes, and can be ascertained in part through (sub)millimeter observations, which permit the measurement of sub-surface thermophysical properties at millimeter to meter depths. We present observations of Europa at ~3, 1.3, and 0.87 mm acquired with the Atacama Large Millimeter/submillimeter Array (ALMA) in 2016 and 2017, with a spatial resolution of ~0.1-0.15’’ (corresponding to ~400-600 km at Europa). We derive hemispheric brightness temperatures and global thermal inertia and porosity values from ALMA thermal emission maps of both the leading and trailing hemispheres in all three frequency bands. These observations allow for the investigation of porosity variations with depth and longitude, while temperature anomalies (i.e. features not well matched by the global best-fit properties) can be compared to local surface features seen in past optical imagery (e.g. impact craters). These measurements improve our understanding of the material properties of Europa between the surface and the deeper crust, as sensed by infrared and radar measurements respectively, and of the modification of icy surfaces by external or internal sources more broadly.

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