A new series of daytime images of Europa from the Atacama Large Millimeter/submillimeter Array (ALMA) has helped astronomers create first global thermal maps of this icy moon.

Evidence strongly suggests that beneath its thin veneer of ice, Europa has an ocean of briny water in contact with a rocky core.

Europa also has a comparatively young surface, only about 20 to 180 million years old, indicating that there are as-yet-unidentified thermal or geologic processes at work.

Unlike optical telescopes, which can only detect sunlight reflected by planetary bodies, radio and millimeter-wave telescopes like ALMA can detect the thermal ‘glow’ naturally emitted by even relatively cold object in our Solar System, including comets, asteroids, and moons.

NRAO astronomer Bryan Butler and Caltech researchers Samantha Trumbo and Michael Brown compared the new ALMA observations of Europa to a thermal model based on observations from NASA’s Galileo spacecraft.

This comparison allowed the team to analyze the temperature changes in the data and construct the first-ever global map of Europa’s thermal characteristics.

The new data also revealed an enigmatic cold spot on Europa’s northern hemisphere.

“These ALMA images are really interesting because they provide the first global map of Europa’s thermal emission,” Dr. Trumbo said.

“Since Europa is an ocean world with potential geologic activity, its surface temperatures are of great interest because they may constrain the locations and extents of any such activity.”

“Studying Europa’s thermal properties provides a unique means of understanding its surface,” Dr. Butler said.

The results were published in the Astronomical Journal.

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Samantha K. Trumbo et al. 2018. ALMA Thermal Observations of Europa. AJ 156, 161; doi: 10.3847/1538-3881/aada87