This is an picture of the Lunar Prospector spacecraft, which was used to determine the size of the Moon's core.
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Image courtesy of NASA

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Read about one of Prospector's other discoveries

Earth's Moon--A Chip Off The Old Block?
News story originally written on March 19, 1999

Scientists have used the Lunar Prospector spacecraft to find out that the Moon has a small core. This supports the formation theory that the Moon was once part of Earth created by a large impact.

Lunar Prospector used gravity measurements to find out how big the Moon's core is. The Moon's core only is more than eight times smaller than the Earth's core.

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