Differences in gravity as measured by the GRAIL mission’s two probes have helped scientists understand the Moon’s interior.

The Moon, no matter what Pink Floyd says, doesn’t have a dark side…unless, of course, you count the inside. All of our telescopes and cameras see only the light reflected off of the surface, leaving the vast interior of the Earth’s Moon unseen. But by measuring the slight irregularities in the Moon’s gravity field, we are able to probe its interior structure from the surface to the core.

In 2012, NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission orbited the Moon and mapped its gravity field in unprecedented detail, revealing some incredible surprises lurking beneath the lunar surface.

Jeffrey Andrews-Hanna, an associate professor in the University of Arizona Lunar and Planetary Laboratory, will discuss GRAIL and what it has revealed about Earth’s closest neighbor in a 3:30 p.m. Thursday (Oct. 12) lecture at the Arizona Senior Academy. Andrews-Hanna was involved in data research from the GRAIL observations.

Jeffrey Andrews-Hanna

This ingenious mission used the moon’s own gravity to study the lunar interior. Its twin craft orbited the moon, maintaining the most precisely equal distance from each other that they could. Little variations in distance between GRAIL-A and GRAIL-B occurred as they flew over areas of greater and lesser gravity. Just as on Earth, the slight change in gravity will be caused both by visible features such as mountains and craters – and by masses hidden beneath the moon’s surface.

Those hidden masses – which scientists call “mascons,” for “mass concentrations,” – are what cause one face of the moon to stay pointed in Earth’s direction. Scientists are itching to learn more about them, because, they say, this knowledge will help us understand how the moon evolved.

Written by Charles Prewitt, Academy Village Volunteer

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Oct. 12: The Dark Side of the Moon
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