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NASA Observes Moon's Tidal Bulge from Lunar Orbit

  • VOA News

Illustration of Earth as seen from the moon. The gravitational tug-of-war between Earth and the moon raises a small bulge on the moon. The position of this bulge shifts slightly over time.

Illustration of Earth as seen from the moon. The gravitational tug-of-war between Earth and the moon raises a small bulge on the moon. The position of this bulge shifts slightly over time.

The moon’s gravity is responsible for the rise and fall of the ocean’s tides, but the Earth has a similar effect on the moon.

Scientists at the U.S. space agency, NASA, say they’ve been able to observe, for the first time from lunar orbit, a “bulge” in the moon caused by the “gravitational tug-of-war with Earth.”

“The deformation of the moon due to Earth’s pull is very challenging to measure, but learning more about it gives us clues about the interior of the moon,” said Erwan Mazarico, a scientist with the Massachusetts Institute of Technology in Cambridge, Mass., who works at NASA’s Goddard Space Flight Center in a statement.

NASA scientists said the gravitational effects on both the Earth and moon are powerful enough to stretch them enough “so they wind up shaped a little like two eggs with their ends pointing toward one another.”

While we can observe the moon’s effect on Earth by watching the ocean’s tides, the effect on the moon is harder to observe because the moon is basically solid except for a small core. Also, only one side of the moon faces the Earth.

Still, scientists said the Earth’s gravity is strong enough to create a 51 centimeter high bulge on both the near and far sides of the moon.

NASA said the lunar bulge “shifts a few inches over time,” responding “to Earth’s movements like a dance partner, following wherever the lead goes.”

The NASA scientists used data from the Lunar Reconnaissance Orbiter, which has been investigating the moon since 2009, and from the Gravity Recovery and Interior Laboratory, or GRAIL, mission. This allowed them to observe the entire moon rather than the one side that constantly faces Earth.

Using the altimeter aboard the LRO, to measure 350,000 locations on the lunar surface. They then compared changes in altitude to see how the bulge had moved.

The study was published online in Geophysical Research Letters.

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