Featured Image: Saturn’s Moon Phoebe Is a Water-Rich Rock

These maps of Saturn’s moon Phoebe show different views of the water-ice absorption across a model of Phoebe’s surface, revealing the body’s icy-rock nature. At 213 km across, Phoebe is the largest of Saturn’s highly inclined irregular satellites, thought to have been captured long ago from the outer solar system. In a recent publication, scientists Wesley Fraser (Queen’s University Belfast, UK) and Michael Brown (California Institute of Technology) have reanalyzed high-resolution spectral imaging of this moon from Cassini’s flyby to explore the water-ice distribution across Phoebe’s surface. Fraser and Brown use their observations to argue that Phoebe’s surface was once quite water poor; its current water-rich state is a consequence of a violent history of impacts, which dredged up water-rich subsurface material. Impact histories like Phoebe’s may explain why there’s so much variation in the amount of water-ice seen on outer-solar-system bodies: more collisions may mean more water-ice. To learn more about the study (and to see more awesome maps and images of Phoebe’s surface!), check out the article below.


Wesley C. Fraser and Michael E. Brown 2018 AJ 156 23. doi:10.3847/1538-3881/aac213