The Moon’s secret history

A topographic map of the Moon (low elevations in purple, high in red) shows extensive lava flows on the Ocean of Storms. New data from the GRAIL spacecraft suggests the region was formed by ancient volcanic activity, not by a large impact as had long been suspected. The image was rendered by Jay Dickson from Brown University with data from NASA's Lunar Reconnaissance Orbiter and Lunar Orbiting Laster Altimeter.
Jay Dickson / Brown University

The “man in the Moon”, the face-like pattern on the Moon’s surface, was caused by ancient volcanic activity and not by an asteroid strike as previously believed, scientists say.

Measurements taken by NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission to the Moon, have caused scientists to reassess how the giant plain on the nearside of the Moon, also known as the Ocean of Storms, came to be.

It was once believed that a rocky ridge on the edges of the 3200 km-wide plain was created when an asteroid crashed into the Moon. But maps made with the help of the GRAIL orbiters found the rocky border was not circular, as one would expect from a meteor impact, but polygonal.

The latest theory is that these lines were produced by giant cracks in the Moon’s crust as it cooled around a plume of hot material from the interior.

“How such a plume arose remains a mystery,” said Maria Zuber, who is principal investigator for the GRAIL mission.

Scientists believe the magma rose to just beneath the Moon’s surface, cooling and crystallising over time. The data from GRAIL, gathered over nine months in 2011 and 2012, have deepened their understanding of the Moon. The results of their study have been published in Nature.

The authors say their investigation has challenged our understanding of the Moon’s evolution – and of what caused the man in the Moon pattern of light and shade on the Ocean of Storms.

“A lot of things in science are really complicated, but I’ve loved to answer simple questions,” said Zuber. “How many people have looked at the Moon and wondered what produced the pattern we see – let me tell you, I’ve wanted to solve that one!”

The full moon as seen from Earth. Gravitational anomalies surrounding the Ocean of Storms region are superimposed in red. New research suggests these anomalies were once the source of a massive lava flow on the moon
Kopernik Observatory/NASA/Colorado School of Mines/MIT/JPL/Goddard Space Flight Centre

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