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    The Crust & Interior of the Moon

         This drawing shows what the interior of the Moon might be like.
          Click on image for full size version (*92K GIF*)

The picture shows the moon's crust, about 60=150 km thick, followed by the
lithosphere </tour/link=/earth/interior/earths_crust.html&edu=high>, shown
in blue. The moon's lithosphere is the major portion of the interior,
about 1000 km thick. The moon's core
</tour/link=/glossary/det_of_interior_layers.html&edu=high> 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
</tour/link=/earth/Magnetosphere/earth_magnetic_reversals.html&edu=high>,
the Moon's crust seems to contain some magnetism
</tour/link=/earth/moon/lunar_crustal_magnetism.html&edu=high>. 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 </tour/link=/earth/moon1.html&edu=high>) 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.