Callisto's near-surface studied using ALMA thermal images

Researchers analyzed six archival ALMA thermal images from 2012 to probe the top few centimeters of Callisto's regolith and estimated a surface temperature near 133 K; the study refines regolith composition maps and indicates subsurface temperature variations.

Researchers used archival observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate the shallow subsurface of Jupiter's moon Callisto. The team analyzed six thermal images taken between July and November 2012 and compared those results with archival data from NASA's Galileo spacecraft. The study, accepted by The Planetary Science Journal, aimed to establish a baseline temperature and improve models of the uppermost regolith. Callisto is an outer Galilean satellite noted for heavy cratering and is hypothesized to host a subsurface liquid water layer. Key findings: - The analysis used six ALMA thermal images recorded from July 17 to November 4, 2012. - The study focused on the top few centimeters of Callisto's surface and compared those observations with Galileo-era data. - The researchers estimated a surface temperature of about 133 K (approximately −140°C). - The work produced improved mappings of regolith composition across different terrain types and reported variations in inferred subsurface temperatures. - The authors note that future ALMA observations and measurements by the ESA JUICE mission (arrival at Jupiter around 2031) can enhance spatial and spectral coverage and help constrain the depth dependence of Callisto's thermal properties. Summary: These results provide a baseline thermal picture of Callisto's uppermost regolith and refine knowledge of surface composition. Future ALMA campaigns and upcoming JUICE observations should improve spatial resolution and extend thermal maps in depth, allowing more detailed study of subsurface temperature structure.