Gravitational forces between the Earth and the moon are causing both our own world and its companion satellite to distort into egg-like shapes. This is caused by tidal forces, which raise the height of water (and to a lesser degree, land), making oceans rise onto beaches on Earth.
Tidal forces on the moon are difficult to study, since the body has a small core, and is gravitationally locked to our planet, with one hemisphere permanently turned toward 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 the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts and NASA's Goddard Space Flight Center in Maryland, said.
Researchers carefully examined data from a pair of NASA missions to study how gravitational forces between the bodies affects our planetary companion. Data from the Lunar Reconnaissance Orbiter (LRO), which has been studying the moon since 2009 was examined. This was added to information from the Gravity Recovery and Interior Laboratory (GRAIL) mission, a pair of craft which orbited the moon from March to December 2012. These orbiters recorded data from all around the moon, including the side never seen by Earth-bound observers.
Tidal forces from the Earth on the moon can raise the lunar surface by 20 inches on the sides both directly facing and opposite our world. The angle and formation of the moon's orbit causes our world, as seen from our satellite, to "wobble around" in one patch of sky. As the pair each swing around their common center of gravity, the bulge slowly shifts, like a dancer following her partner.
"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," Mike Barker co-author of the new study, stated in a NASA press release.
Researchers studied the height of the lunar surface using the Lunar Orbiter Laser Altimeter (LOLA) aboard the LRO. In areas where the spacecraft passed over more than once, researchers could easily calculate how much the surface had risen, or lowered, over time. The purpose of the GRAIL mission was to explore fine detail of the moon's gravitational field, examining small anomalies that were first discovered during the 1960,s as NASA planned for the Apollo missions. This information detailed mass concentrations that affect how the surface reacts to tidal forces.
The investigation of how tidal forces affect the moon was detailed in the journal Geophysical Research Letters.
