5. The Moon: stepping stone to the planets
Inside the Moon
Moonquakes have been recorded by sensitive seismometers left on the lunar surface, and used to infer the internal structure of the Moon. The Moon is slightly asymmetrical in bulk form, with a thicker crust on the far side. Most of the volcanic maria occur on the near side where the crust is thinner. On average, the lunar crust is about 70 thousand meters thick. It is only a few tens of thousands of meters thick beneath the mare basins, but over 100 thousand meters thick in the highlands and the far side of the Moon. As a result, the Moon's center of mass is offset from its geometric center by about 2 thousand meters in the direction of the Earth. Data from Lunar Prospector obtained in 1998-1999, indicate that the Moon's iron-rich core has a radius of 350 thousands meters, or 20 percent of the satellite's radius, and only about 2 percent of the body's mass.
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Copyright 2010, Professor Kenneth R. Lang, Tufts University