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The Once and Future Moon

The Lunar Surface – What Lies Beneath

10 Dec 2012, 20:36 UTC
The Lunar Surface – What Lies Beneath
(200 words excerpt, click title or image to see full post)

Gravity data from NASA's GRAIL mission show that deeply buried bodies of igneous rock in the crust can be detected from orbit.

Map of the gravity gradients of the Moon as recorded by the GRAIL spacecraft (NASA)
The NASA mission GRAIL (Gravity Recovery And Interior Laboratory) has been orbiting the Moon since last spring. The mission consists of two identical small spacecraft (dubbed Ebb and Flow) that very carefully keep track of their relative position from each other. By tracking both of these spacecraft with high precision from Earth, we can monitor any small variations (caused by variations in the Moon’s gravity field) away from their predicted orbital paths. If the satellite is flying over an area on the Moon with less material than normal (for example, over a deep crater, a hole in the Moon’s crust), it will be less attracted to the Moon because of this mass deficiency and will therefore fly away from the Moon. If, on the other hand, it flies over an area of excess mass, such as a thick stack of dense lava flows, the excess mass pulls the satellite slightly toward it, increasing its speed and pulling it downwards. As Ebb and Flow ...

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