Last September, NASA launched a pair of twin spacecrafts, named Ebb and Flow, to get a closer look at the moon’s gravity. The mission was called Gravity Recovery and Interior Laboratory, better known as GRAIL. The spacecraft chase each other around the moon, varying from four to more than 125 miles apart. The change in distance between the two probes varies as they move over areas of greater and lesser gravity. As the first spacecraft goes over a mountain, for example, it will speed up. Since topographic features of different densities and composition — like mountains versus valleys — exert different gravitational pulls, researchers match changes in gravity with structures like mountains, impact craters, and volcanic landforms. The result is a more complete picture of the moon’s interior.
During the mission phase, which stretched from March to May 2012, the two washing-machine-sized spacecraft created a high-resolution map of the moon’s gravity field that revealed many never-before-seen details about the moon’s internal structure, including evidence of volcanic structures beneath the moon.
The findings were presented Wednesday, Dec. 5, at the American Geophysical Union meeting in San Francisco and published online by the journal Science.
“We used gradients of the gravity field in order to highlight smaller and narrower structures than could be seen in previous datasets,” GRAIL scientist Jeff Andrews-Hanna of the Colorado School of Mines said in a statement.
“This data revealed a population of long, linear gravity anomalies, with lengths of hundreds of kilometers, crisscrossing the surface. These linear gravity anomalies indicate the presence of dikes, or long, thin, vertical bodies of solidified magma in the subsurface. The dikes are among the oldest features on the moon, and understanding them will tell us about its early history,” he added.
So, it would seem that there are hidden volcanoes on the moon!
The movie below shows the variations in the lunar gravity field as measured by the twin spacecraft. Red corresponds to mass excesses (like mountains) and blue corresponds to mass deficiencies (like craters).
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