Moon's 'Dancing Tide' Sways with Earth's Pull

NASA missions in orbit have for the first time allowed scientists to observe the Moon's "dancing tide" swaying with Earth's gravitational pull.

The team drew on studies by NASA's Lunar Reconnaissance Orbiter (LRO), which has been investigating the moon since 2009, and by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. Since these spacecraft orbit around the Moon, scientists could assess the orb from every angle, not just from the side seen from 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," Erwan Mazarico, from NASA's Goddard Space Flight Center, said in a news release.

The Moon's lopsided shape can be explained by its gravitational tug-of-war with Earth. The mutual pulling of the two planetary bodies, in fact, is powerful enough to stretch each one into the shape of an egg with their ends pointing toward one another. On Earth, this affect can drive the tides of the oceans.

It's difficult to detect Earth's affect on the Moon, given that the Moon is mostly solid except for its small core. Even so, there's still enough pull so that a 20-inch-high bulge is created on its near and far sides. What's more interesting is that this bulge shifts over time, demonstrating that the Moon actually sways with Earth's movements in a cosmic dance.

"If nothing changed on the Moon - if there were no lunar body tide or if its tide were completely static - then every time scientists measured the surface height at a particular location, they would get the same value," said co-author Mike Barker, a Sigma Space Corporation scientist based at Goddard.

To further investigate the tide's signature, scientists took data from LRO's Lunar Orbiter Laser Altimeter (LOLA), which mapped the height of features on the Moon's surface. They were able to take a more direct measurement of the lunar body tide and receive much more comprehensive coverage than ever before.

In turn, it could help with future studies when it comes to gravitational forces that shape the Moon and its dancing partner Earth.

The findings are published in the journal Geophysical Research Letters.