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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

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

Scientists have used data from the Lunar Prospector spacecraft to determine that the Moon has a small core. This finding supports the formation theory that the Moon was once part of Earth and was ejected following a large impact.

"This impact occurred after the Earth's iron core had formed, ejecting rocky, iron-poor material from the outer shell into orbit," explained Dr. Alan Binder, principal investigator for Lunar Prospector. "It was this material that collected to form the Moon."

Lunar Prospector used gravity measurements to determine the size of the Moon's core. It contains less than four percent of the Moon's mass. The Earth's core on the other hand contains 30 percent of our planet's mass.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA