New data from NASA's GRAIL mission suggest that the crust of the Moon is thinner than we had thought. Is this idea consistent with the geological evidence?
Map of the thickness of the Moon's crust from GRAIL mission gravity data. Mean thickness are estimated to be 34-43 km.
Imagine a system of molten silicate material, where low-density minerals float and higher density minerals sink. Minerals rich in iron and magnesium (such as olivine and pyroxene) will settle toward the bottom of the magma body while those rich in the elements aluminum and calcium (such as plagioclase feldspar) will float. Just such a scenario – on a global basis – is thought to have created the crust of the Moon.
Before Apollo, many believed that the Moon was a primitive, undifferentiated lump of cosmic debris. By studying the samples returned by Apollo 11, scientists identified small fragments of white, plagioclase-rich rocks (anorthosite). There are no known magma compositions corresponding to this rock type – anorthosite is created by removing low-density plagioclase from a crystallizing system and concentrating it by floatation. From the evidence of fragments in the lunar soil, large amounts of anorthosite were inferred to be present in the nearby ...