Using data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL), mission scientists have solved a lunar mystery almost as old as the Moon itself.
Early theories suggested the craggy outline of a region of the Moon’s surface known as Oceanus Procellarum, or the Ocean of Storms, was caused by an asteroid impact. If this theory had been correct, the basin it formed would be the largest asteroid impact basin on the Moon. However, mission scientists studying GRAIL data believe they have found evidence the craggy outline of this rectangular region — roughly 1,600 miles (2,600 kilometers) across — is actually the result of the formation of ancient rift valleys.
“The near side of the Moon has been studied for centuries, and yet continues to offer up surprises for scientists with the right tools,” said Maria Zuber, principal investigator of NASA’s GRAIL mission, from the Massachusetts Institute of Technology, Cambridge. “We interpret the gravity anomalies discovered by GRAIL as part of the lunar magma plumbing system — the conduits that fed lava to the surface during ancient volcanic eruptions.”
The surface of the Moon’s near side is dominated by a unique area called the Procellarum region, characterized by low elevations, unique composition and numerous ancient volcanic plains.
The rifts are buried beneath dark volcanic plains on the near side of the Moon and have been detected only in the gravity data provided by GRAIL. The lava-flooded rift valleys are unlike anything found anywhere else on the Moon and may at one time have resembled rift zones on Earth, Mars and Venus.
Earth’s moon as observed in visible light (left), topography (center, where red is high and blue is low), and the GRAIL gravity gradients (right). The Procellarum region is a broad region of low topography covered in dark mare basalt. The gravity gradients reveal a giant rectangular pattern of structures surrounding the region. Image Credit: NASA/GSFC/JPL/Colorado School of Mines/MIT.