Earth’s Gravity Is Reshaping the Moon

Leaving cracks on the surface as it slowly contracts

Moon surface

The moon is shrinking and it’s all thanks to the Earth.

NASA scientists have known since 2010 that the moon is slowly getting smaller, but according to a new study of cracks on the moon’s surface, it appears that the Earth’s tides are also helping reshape the surface of the moon. While the moon plays a part in influencing the ocean’s tides, it turns out that tidal forces go both ways, influencing how the cracks formed, Rachel Feltman writes for The Washington Post.

“There is a pattern in the orientations of the thousands of faults, and it suggests something else is influencing their formation, something that’s also acting on a global scale,” Tom Watters, the study’s author and researcher at the Smithsonian’s National Air and Space Museum said in a press release. “That something is the Earth’s gravitational pull.”

Watters first noticed these cracks in photographs taken by NASA’s Lunar Reconnaissance Orbiter (LRO) in 2010. Much as on other moons and planets in the solar system, these cracks are formed when the molten core of a celestial body cools down, causing the surface to contract.

"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," Watters said in a statement in 2010. "Based on the size of the scarps, we estimate the distance between the moon's center and its surface shrank by about 300 feet.”

Back in 2010, lunar images had only mapped a fraction of the moon’s surface and uncovered only 14 scarps. Since then, the LRO has covered almost 75 percent of the moon and identified over 3,200 scarps across its surface. When Watters examined the new images of the cracks, most of them appeared to run east to west near the moon’s poles and north to south by its equator – a curious thing, as they should have appeared randomly across the moon’s surface, as they do on other planets and moons where scientists have observed them. The only reason the scarps would have formed in such an orderly fashion is if an external force was tugging on the moon’s surface as it shrunk, Adam Epstein writes for Quartz.

When Watters and his team saw these patterns, they realized that they were strikingly familiar to Earth’s own tidal patterns near the poles and the equator. Essentially, Watters writes in a study published in the October issue of the journal Geology, the Earth’s tidal forces are acting on the moon’s surface much as the moon influences the Earth’s oceans.

“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,” Watters said in a statement.

h/t The New York Times

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