How the Moon Got Its 'Face'

By: CBS News (Posted by Doug Meyers)
By: CBS News (Posted by Doug Meyers)

Have you ever wondered what gives the moon its face-like features? Scientists now say they have an answer.

The near side of the moon has larger impact craters than the far side. These formed during a period about four billion years ago. The near-side craters comprise what we think of as the face of the moon.

"Since time immemorial, humanity has looked up and wondered what made the man in the moon," Maria Zuber, a geophyisics professor the Massachusetts Institute of Technology (MIT) and the principal investigator with NASA's Gravity Recovery and Interior Laboratory (GRAIL), said in a press release.

"We know the dark splotches are large, lava-filled, impact basins that were created by asteroid impacts about four billion years ago. GRAIL data indicate that both the near side and the far side of the moon were bombarded by similarly large impactors, but they reacted to them much differently."

During the Late Heavy Bombardment (LHB) of 4 billion years ago, the entire solar system was pummeled by an asteroid hailstorm. The evidence is more visible on the moon than on young planets from the time, like Earth, because the Earth's plate tectonics and erosion have erased the scars.

Scientists from MIT and the University of Paris looked at data collected as NASA's GRAIL probes circled the moon from January to December 2012. They created a map of the moon's crust, noting the thickness in each area. The data shows that the crust on the near side is thinner than it is on the far side.

Next, they looked at volcanic activity on the moon and internal temperatures. The near-side surface had hotter internal temperatures, making it more susceptible to damage when the asteroids struck.

"Impact simulations indicate that impacts into a hot, thin crust representative of the early moon's near-side hemisphere would have produced basins with as much as twice the diameter as similar impacts into cooler crust, which is indicative of early conditions on the moon's far-side hemisphere," notes Miljkovic.

This indicates that the asteroid impacts had less to do with the "face of the moon" than did internal temperatures and volcanic activity.

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