ALMA Thermal Observations of Europa

TL;DR

This study presents the first spatially resolved thermal images of Europa's surface using ALMA, revealing variations in thermal properties and identifying an anomalously cold region, advancing understanding of Europa's surface composition and thermal behavior.

Contribution

It provides the first complete, high-resolution thermal dataset of Europa's surface and links thermal variations to surface properties using a global thermal model.

Findings

Large-scale thermal structure driven by albedo variations

Localized discrepancies explained by surface property inhomogeneity

Identification of an anomalously cold region near 90°W, 23°N

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.