NASA says its Gravity Recovery and Interior Laboratory mission uncovered the origin of massive regions inside the moon that make its gravity uneven. GRAIL's findings may help spacecraft on missions to other celestial bodies navigate with greater precision in the future, the space agency said Thursday. In a nine-month mission, GRAIL's twin spacecraft studied the internal structure and composition of the moon in unprecedented detail, pinpointing the locations of large, dense regions called mass concentrations, or mascons, characterized by strong gravitational pull. Mascons are located beneath the lunar surface and cannot be seen by normal optical cameras, researchers said. "GRAIL data confirm that lunar mascons were generated when large asteroids or comets impacted the ancient moon, when its interior was much hotter than it is now," Jay Melosh, a GRAIL co-investigator at Purdue University, said. "We believe the data from GRAIL show how the moon's light crust and dense mantle combined with the shock of a large impact to create the distinctive pattern of density anomalies that we recognize as mascons." On a map of the moon's gravity field, a mascon appears in a target pattern, with a bulls-eye possessing a gravity surplus surrounded by a ring with a gravity deficit. An outer ring with a gravity surplus surrounds the bulls-eye and the inner ring. The increase in density and gravitational pull at a mascon's bulls-eye is caused by lunar material melted from the heat of a long-ago asteroid impact, researchers said. "Knowing about mascons means we finally are beginning to understand the geologic consequences of large impacts," Melosh said. "Our planet suffered similar impacts in its distant past, and understanding mascons may teach us more about the ancient Earth, perhaps about how plate tectonics got started and what created the first ore deposits."