Procellarum lunar region. Gravity anomaly map of rifts surrounding the edge of the Moon's Oceanus Procellarum (Ocean of Storms) region. The gravity anomalies (red) suggest that this feature formed as a sea of basaltic lava as the lunar crust cooled billions of years ago. According to this theory, magma rose from the Moon's interior to flood low lying areas with lava (molten rock). This image shows data from the Gravity Recovery and Interior Laboratory (GRAIL) probes which operated in lunar orbit from March to December 2012. This image and the associated research was published in 2014.