Zothecula writes with an update on NASA's lunar mapping probes. From the article: "After entering orbit around the Moon at the start of the year, NASA's twin GRAIL probes, Ebb and Flow, have completed their primary mission to study the Moon's interior structure ahead of schedule. Operating around the clock since March 8, NASA says the spacecraft have provided unprecedented detail about the interior structure and evolution of the Moon and the data they have gathered will provide insights into how Earth and its rocky neighbors in the inner solar system developed." And their extended mission? From NASA: "The extended mission goal is to take an even closer look at the moon's gravity field. To achieve this, GRAIL mission planners will halve their current operating altitude to the lowest altitude that can be safely maintained. 'Orbiting at an average altitude of 14 miles (23 kilometers) during the extended mission, the GRAIL twins will be clearing some of the moon's higher surface features by about 5 miles (8 kilometers),' said Joe Beerer of JPL, GRAIL's mission manager."