The moon is shrinking and more faults are opening up in the lunar crust. The likely culprit? Earth’s own gravitational pull.

Using images from NASA’s Lunar Reconnaissance Orbiter (LRO), scientists found that the gravitational pull of Earth is opening up faults on the moon, nearly three-fourths of which have been imaged at high resolution.

It has long been established that the gravitation field of Earth exerts a tidal force on the moon, and that lunar gravity has a hand in the rise and fall of waters in Earth's oceans and lakes. Research, however, only recently confirmed that the pull from Earth is creating faults on the moon’s surface.

After over six years in orbit, the LRO has discovered more than 3,200 more of these faults.

“These globally distributed faults have emerged as the most common tectonic landform on the moon,” stated the official NASA release on the fault scarps. Analyzing the orientations and formations of the scarps led NASA to the conclusion that the faults manifested during the moon’s life span as its liquid core cooled and solidified, causing the lunar surface to shrink and crack.

These lunar cliffs, the moon’s most common tectonic feature, are usually dozens of yards tall and less than about 6 miles long. Previous studies suggest that these were no more than 50 million years in age and are still probably in active formation today.

Researchers said it was "a big surprise" that the faults do not exhibit random orientations if they are solely influenced by the cooling of the moon's interior. 

Something else is exerting influence on their formation and that is the Earth’s gravity, said planetary scientist Thomas Watters of the Smithsonian's National Air and Space Museum and lead author of the study published in the journal Geology.

Data also showed that the peak stresses are reached when the moon is at apogee or at its greatest distance from Earth in its orbit. During this time, there may be shallow "moonquakes" along the active faults. These can be detected and studied using a lunar seismic network in the future.

According to John Keller, LRO project scientist at the Goddard Space Flight Center, the extent of investigation on the moon made possible by the LRO is not yet doable for any other entity in the solar system beyond Earth. The LRO data set allows scientists to “tease out subtle but important processes” that would otherwise stay unknown, he said.

LRO was launched on June 18, 2009 and uses seven instruments to collect data. It is managed by the Goddard Space Flight Center in Maryland under the Science Mission Directorate at NASA headquarters in Washington.

Photo: Janet Ramsden | Flickr

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