Moon’s Blotchy Near Side Has Bigger Craters Than Expected

by Elizabeth Howell on November 13, 2013

The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic

The thickness of the moon’s crust as calculated by NASA’s GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic

The familiar blotches that make up “the man in the moon”, from the vantage point of Earth, happened because the moon’s crust is thinner on the near side than the far side to our planet, new research reveals.

The twin GRAIL spacecraft provided the most accurate sizes yet of lunar impact craters on the moon, providing more insight into what happened when Earth’s closest large neighbor was hammered with meteorites over billions of years.

“Since time immemorial, humanity has looked up and wondered what made the man in the moon,” stated Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology in Cambridge.

Artist's conception of the twin GRAIL spacecraft, called Ebb and Flow. Credit: NASA/JPL-Caltech

Artist’s conception of the twin GRAIL spacecraft, called Ebb and Flow. Credit: NASA/JPL-Caltech

“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.”

The moon’s near side is easily visible in a telescope, but it’s hard to measure the size of the impacts because lava is obscuring their dimensions. The GRAIL spacecraft, however, peered at the internal structure of the moon and also produced information showing how thick the crust is. This showed that there are more, bigger craters on the closer side of the moon to us than the further side.

Closeup of the Moon showing Endymion, Atlas and the distant Mare Humboldtianum. Credit and copyright: Danny Robb.

Closeup of the Moon showing Endymion, Atlas and the distant Mare Humboldtianum. Credit and copyright: Danny Robb.

“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,” stated lead author Katarina Miljkovic of the Paris Institute of Earth Physics (Institut de Physique du Globe de Paris).

As is common with research projects, learning more about the moon is revealing a new mystery that needs to be examined. It’s commonly cited that the moon was walloped during something called the late heavy bombardment, a period four billion years ago when it was believed that more meteorites impacted the moon.

“The late heavy bombardment is based largely on the ages of large near-side impact basins that are either within, or adjacent to the dark, lava-filled basins, or lunar maria, named Oceanus Procellarum and Mare Imbrium,” NASA stated.

“However, the special composition of the material on and below the surface of the near side implies that the temperatures beneath this region were not representative of the moon as a whole at the time of the late heavy bombardment. The difference in the temperature profiles would have caused scientists to overestimate the magnitude of the basin-forming impact bombardment.”

A research paper on the topic recently appeared in Science. GRAIL successfully concluded its mission last year after nine months of operations, flying into the side of a mountain as planned.

Source: NASA

 

About 

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

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