We head out to Jupiter to revisit an old friend of the show, Ganymede. In a new paper published in The Planetary Science Journal, a team of scientists analyzed data from the Atacama Large Millimeter/submillimeter Array (ALMA) taken at several different millimeter wavelengths to create a thermal model of Jupiter’s largest moon. This data allowed them to create a global temperature map and identify a few interesting features.

First off, Ganymede gets more densely packed the further below the surface you go, dropping from 85% porosity to 10%. The more porous the rock, the more easily it responds to changes in heating, so the outer surface will react more quickly than the subsurface rock. That means just a little heat from the daytime sunlight, even at that distance, could have a substantial effect on the expansion and contraction of the surface.

Next, there are a few craters that are cooler than expected, which could mean some localized variation in composition, porosity, or even the properties of the grains of rock. Maybe even some combination of those qualities.

Last but definitely not least, there are a few large-scale deviations in the temperatures expected: excess heat was measured at the equator, and at the middle latitudes, cooler temps. These results likely mean that Ganymede’s surface temperatures are mostly influenced by external processes such as micrometeorite and plasma bombardment from Jupiter.

The team is planning to do further studies using ALMA data, including more analysis of Ganymede as well as Jupiter’s moons Europa and Callisto. We’ll bring you those results here on the Daily Space when they are available.

More Information

AAS Nova article

“Ganymede’s Surface Properties from Millimeter and Infrared Thermal Emission,” Katherine de Kleer et al., 2021 January 22, The Planetary Science Journal