ALMA Thermal Observations of Europa

Abstract

We present four daytime thermal images of Europa taken with the Atacama Large Millimeter Array. Together, these images comprise the first spatially resolved thermal dataset with complete coverage of Europa's surface. The resulting brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a typical linear resolution of roughly 200 km. At this resolution, the images capture spatially localized thermal variations on the scale of geologic and compositional units. We use a global thermal model of Europa to simulate the ALMA observations in order to investigate the thermal structure visible in the data. Comparisons between the data and model images suggest that the large-scale daytime thermal structure on Europa largely results from bolometric albedo variations across the surface. Using bolometric albedos extrapolated from Voyager measurements, a homogenous model reproduces these patterns well, but localized discrepancies exist. These discrepancies can be largely explained by spatial inhomogeneity of the surface thermal properties. Thus, we use the four ALMA images to create maps of the surface thermal inertia and emissivity at our ALMA wavelength. From these maps, we identify a region of either particularly high thermal inertia or low emissivity near 90 degrees West and 23 degrees North, which appears anomalously cold in two of our images.

arXiv comment9 pages, 3 figures, accepted for publication in the Astronomical Journal

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• Global regolith thermophysical properties of the Moon from the Diviner Lunar Radiometer Experiment
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• LunaIcy: Exploring Europa's Icy Surface Microstructure through Multiphysics Simulations
• MultIHeaTS: A Fast and Stable Thermal Solver for Multilayered Planetary Surfaces
• Revealing the dynamics of magnetosphere, atmosphere, and interior of solar system objects with the Square Kilometre Array