Strikingly Geometric’ Rifts Upturn Theories of Moon’s Formation

This series of images show the moon as seen in visible light (left), its topography (center; red is high terrain, blue is low), and NASA's GRAIL gravity measurements (right). The moon's Ocean of Storms is a broad region of low topography covered in dark mare basalt, with gravity measurements revealing a giant rectangular pattern of structures around the area. NASA/Colorado School of Mines/MIT/JPL/Goddard Space Flight Center

In a surprising revision to earlier theories, researchers report that a massive feature on the moon formed due to lunar rifts.

Scientists had previously thought the Ocean of Storms, also known as Oceanus Procellarum, was created by a giant cosmic impact that left a crater about 2,000 miles wide (3,200 kilometers). But readings from NASA's GRAIL mission reveal that the feature is not round. Instead, it's surrounded by a strange giant rectangle beneath the surface.

This suggests the Ocean of Storms was not caused by a meteor strike, but formed as the moon's surface rifted apart.

The full moon as seen from the Earth, with the Ocean of Storms (Procellarum) border structures superimposed in red. Scientists now think this huge feature on the moon was formed by lunar lava early in the moon's formation, and not a cataclysmic impact. Kopernik Observatory/NASA/Colorado School of Mines/MIT/JPL/Goddard Space Flight Center

"As a solid cools and contracts, fractures and faults can form, and these fractures will commonly take on a polygonal pattern," lead study author Jeffrey Andrews-Hanna of the Colorado School of Mines explained. On the moon, these ancient rift zones took on a rectangular shape.

"The observed pattern of gravity anomalies on the moon is so strikingly geometric and in such an unexpected shape that it is forcing us to think in new and different ways about the processes operating on the moon and planets in general," Andrews-Hanna said.

The research is detailed in Thursday's issue of the journal Nature.

—Charles Q. Choi,

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