A study published Tuesday in the journal Geology suggests that the cracks caused by the moon’s shrinkage are actually influenced by Earth’s gravitational pull.
Back in 2010, researchers using images from NASA’s Lunar Reconnaissance Orbiter (LRO) observed what they called “lobate scarps.” These cliffs were made by small cracks in the moon’s surface, usually less than 6 miles long and all less than 300 feet high, with most of them much smaller.
Scientists recognized them from elsewhere in the solar system: On Mercury, lobate scarps can be hundreds of miles long.
They form when the hot, molten core of a young planet (or moon) cools down. The contraction of the cooling core forces the mantle and surface to squish together, forming the faults.
"We estimate these cliffs, called lobate scarps, formed less than a billion years ago, and they could be as young as a hundred million years," Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum said in a 2010 statement. Since the moon is 4 billion years old, these cracks were surprisingly youthful. "Based on the size of the scarps, we estimate the distance between the moon's center and its surface shrank by about 300 feet,” Watters said.
In the new study, Watters confirms a theory he floated back in 2010. The scarps on the moon should be random, if they’re only influenced by the moon’s shrinkage. But they’re not random — there were patterns in their formation. When he published his 2010 paper, Watters suggested that the Earth’s gravitational pull might be helping to shape the faults.
Since then, the LRO has identified more than 3,000 additional scarps — compared with just 14 in 2010. And the researchers confirmed that their positions made sense, when overlaid with the tidal force of the Earth on the moon.
They also believe, based on the youth of many of the scarps, that more continue to form today.
“The discovery of thousands of young fault scarps, influenced by tidal forces from Earth, is an exciting new dimension to our understanding of the close relationship between our planet and the Moon,” said Watters.