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This drawing shows what the interior of the Moon might be like.
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The Crust & Interior of the Moon

The picture shows the moon's crust, about 60=150 km thick, followed by the lithosphere, shown in blue. The moon's lithosphere is the major portion of the interior, about 1000 km thick. The moon's core may be comprised of two zones, a "soft" partially molten zone and a solid iron zone, as shown in the picture. Moonquakes, as measured by seismometers left behind by the Apollo astronauts, seem to take place between the outer core and the lithosphere.

The Moon's crust is a composed of a dusty outer rock layer called a regolith. The term regolith refers to a rocky layer resembling concrete, which has been broken and blasted apart, then fused back together somehow. Like the Earth's crust, the Moon's crust seems to contain some magnetism. Both the crust and regolith of the Moon are unevenly distributed over the entire Moon. The crust ranges from 38 miles (60 km) on the near side to 63 miles (100 km) on the far side. The regolith varies from 10 to16 feet (3 to 5 meters) in the maria to 33 to 66 feet (10 to 20 meters) in the highlands. Scientists think that such uneveness of the lunar crust most likely accounts for the Moon's off-set center of mass. Crustal uneveness may also explain differences in lunar terrain, such as the dominance of smooth rock (maria) on the near side of the Moon.

The Lunar Prospector Mission expects to explore more about the crust of the Moon. The Gravity Experiment onboard the spacecraft will explore uneveness in the crustal structure and permit a more accurate calculation of the density of the lunar core. This is important information for designing fuel-efficient future lunar missions and landing operations.


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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