The moon has shrunk globally in the past billion years, new high-resolution pictures suggest. The evidence comes in the form of cliffs all over the moon that have formed over the last million millennia like wrinkles on the surface of a dried-out piece of fruit.
Scientists have studied 70 to 80 of these cliffs, called lobate scarps, since the Apollo missions in the ’70s. The scarps are generally tens of kilometers long and less than 100 meters high. Researchers had already hypothesized that the scarps were due to shrinkage, but the Apollo images showed only the moon’s equatorial region. Scientists weren’t sure whether the scarps spanned the entire surface of the moon.
Now, images in the Aug. 20 Science from the Lunar Reconnaissance Orbiter, NASA’s unmanned moon satellite, reveal 14 new scarps from spots all over the moon. It’s the first definitive evidence that the scarps occur globally.
“This is the best observational evidence so far that the lunar cooling and contraction has persisted over the last billion years,” says planetary scientist Sean Solomon of the Carnegie Institution for Science in Washington, D.C.