Galileo Data Suggests Callisto's Ocean Depth Significantly Underestimated

Scientists have re-analyzed data from the Galileo spacecraft, which explored the Jupiter system in the 1990s, revealing new insights about Callisto, one of Jupiter's largest moons. The analysis supports the hypothesis that Callisto harbors a subsurface ocean.Callisto, heavily cratered and approximately the size of a small planet, presents a geologically enigmatic surface. During the 1990s, NASA's Galileo spacecraft conducted magnetic field measurements near Callisto, indicating the potential for a conductive layer beneath its icy crust, suggesting the presence of a salty ocean.However, evidence for Callisto's subsurface ocean has remained inconclusive due to the moon's intense ionosphere. Researchers propose that the conductive upper atmosphere of Callisto could mimic the magnetic signature of a subsurface ocean.The re-examination of Galileo's data involved incorporating all available magnetic field measurements from the spacecraft's close flybys of Callisto. Advanced statistical modeling of the ionosphere and geophysical properties of Callisto was employed to determine the likelihood of a subsurface ocean.The findings suggest that Callisto's ionosphere alone cannot account for the observed magnetic responses, implying the presence of a subsurface ocean. According to the study, the ocean is likely located at a depth of no more than ten kilometers beneath Callisto's icy surface. It could be up to several hundred kilometers deep. Underneath the hypothetical ocean lies a strange, slushy layer of ice.These insights provide a foundation for future spacecraft missions designed to explore ocean worlds, particularly those planned for Jupiter's icy moons. Close-range explorations are scheduled for NASA's Europa Clipper mission and the European Space Agency's JUICE (Jupiter Icy Moons Explorer) mission, both of which are already launched. The planned Chinese mission "Tianwen-4" may also investigate Callisto.