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Thermal millimeter maps of Callisto’s leading and trailing hemispheres obtained with ALMA

Presentation #504.04 in the session Galilean Satellites: Scratching the Surface (Oral Presentation)

Published onOct 23, 2023
Thermal millimeter maps of Callisto’s leading and trailing hemispheres obtained with ALMA

The timeworn surface of Jupiter’s moon Callisto is one of the best records of long-term bombardment the Solar system has to offer. As though its surface were frozen in time, Callisto has seemingly done little more than collect and degrade impact features since its formation 4.5 billion years ago. One outcome of Callisto’s quiescence is that its geologic map retains only a few units, with large-scale landforms consisting of either enormous multi-ring impact basins or crater-laden plains. Despite this geologic simplicity, our knowledgebase of Callisto’s material surface properties is limited compared to the other icy Galilean moons. Mapping the distribution of the physical properties such as thermal inertia and emissivity across a surface can offer key diagnostics regarding the local exogenic and endogenic modification processes. In recent years, observations of thermal emission from Galilean satellites obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) have effectively probed the physical properties of their surfaces at depth (Europa: Trumbo+2017, 2018; Ganymede: de Kleer+ 2021). Here, we complete the icy Galilean satellite ALMA catalogue with the full Callisto dataset which includes leading and trailing hemisphere images at ALMA Bands 7, 6, and 3, corresponding to ~345, ~223, and ~97 GHz, respectively. At these frequencies, we sample the subsurface depths of order a few centimeters down to about half a meter. We model our retrieved brightness temperature maps using a thermophysical model (de Kleer+ 2021) constrained by spacecraft reflectance data to obtain global surface properties including thermal inertia and emissivity. We will present our best-fit surface properties and will discuss thermal anomalies with probable dramatic origins such as impacts, as well as thermal features for which more delicate exogenic mechanisms may be responsible. References: [1] Trumbo, S. K., Brown, M. E., & Butler, B. J. 2017, AJ, 154, 148. [2] Trumbo, S. K., Brown, M. E., & Butler, B. J. 2018, AJ, 156, 161. [3] de Kleer, K., Butler, B., de Pater, I., et al. 2021, PSJ, 2, 5.

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