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Shock waves from ancient lunar impacts may be responsible for creating the Earth’s single most famous face – the “Man in the Moon”.

People have long interpreted a series of dark patches on the Moon’s surface as a human face but no one knew how they formed. Now, scientists at Ohio State University, US, appear to have solved the mystery by creating a topographical model of the Moon and mapping gravity signatures of rocks all the way to the core.

Their findings suggest that the impacts of ancient collisions on the far side of the Moon were so great they caused a corresponding bulge on the near side, and the Earth’s gravitational pull further tugged at this bulge.

Those colossal movements opened cracks in the crust and let magma from the lunar mantle flood onto the surface, at a time when the Moon was still geologically active. This solidified to form what we now see from Earth as the eyes, nose and mouth of the Man in the Moon.

Rocked to the core

“Where you have impact craters, you get an anomalous distribution of mass, and that’s what shows up on the gravity field model,” explains Ralph von Frese, a geologist at Ohio State, and one of the team.

“The impacts were huge enough to disrupt the Moon to its core and at the same time Earth’s gravity field moved mass preferentially to the nearside. Because this happened when the Moon was solidifying, the movements of mass produced a gravity anomaly that we can measure four billion years later.”

The researchers used gravity fluctuations measured by NASA’s Clementine and Lunar Prospector satellites to map the moon’s interior.

Journal reference: Physics of the Earth and Planetary Interiors (DOI: 10.1016/j.pepi.2005.06.013)