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The Interior of the Moon - Windows to the Universe

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The Winter 2010 issue of The Earth Scientist includes a variety of educational resources, ranging from astronomy to glaciers. Check out the other publications and classroom materials in our online store.
This drawing shows what the interior of the Moon might be like.
Click on image for full size

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 asymmetry of the lunar crust most likely accounts for the Moon's off-set center of mass. Crustal asymmetry 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 Doppler Gravity Experiment onboard the spacecraft will explore expected asymmetries in the crustal structure and permit a more accurate calculation of the so-called homogeneity constant, a number which enables scientists to determine 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 by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF