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The Moon Is Shrinking

August 20, 2010

Earth’s next-door neighbor, the Moon, has been found by astronomers to be shrinking, but only by a miniscule amount.

Astronomers reported Thursday in the US journal Science that they had discovered previous undetected cracks in the moon’s crust that formed as the interior cooled and shrunk over the last billion or so years. The finding indicates that the lunar satellite has definitely gotten smaller, though not enough that it would be noticed by just gazing at it.

Scientists have identified 14 landforms, known as lobate scarps, scattered over the surface of the moon, explained Thomas R. Watters of the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum.

The scarps were originally only found at the equator of the moon, but the new findings are the first evidence in other areas, indicating they result from global process. The scarps indicate “evidence of recent thrust faulting on the moon.” But in this case, meaning planetary science, “recent” could mean a billion years.

Watters explained in a telephone interview with The Associated Press that the scarps — or cliffs — extend across some small craters, and small craters tend to be obliterated over time. There are no large craters imposed on top of the scarps, which indicates they are fairly recent, he added.

“One of the really cool parts of this … the faults are so young-looking that you can’t escape the possibility that this contraction occurred recently, and could indicate that the moon is still active,” said Watters.

The size of the scarps suggests that the moon shrank in size by about 328 feet, which wouldn’t be nearly enough to be noticed with the naked eye. The moon is about one-quarter the size of the Earth.

Watters stressed that the moon is not going to disappear and the shrinkage will not affect the Earth in any way.

Lobate scarps were first spotted near the equator in the 1970s by panoramic cameras aboard the Apollo 15, 16 and 17 missions. NASA’s Lunar Reconnaissance Orbiter is responsible for taking the new high-resolution images of the 14 new faults.

The new faults are distributed across the lunar landmass and not clustered in equatorial regions, which provides powerful evidence for the shrinkage scenario.

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