MODEL FOR THE INTERIOR
Seismic data tells us that the crust is about 60 kilometers thick, twice the thickness in kilometers of the earth's crust. The basaltic material of the maria was formed by the impact of large bodies, which provided the energy to melt partially the i ron-rich regions below the crustal layer. Heat flow from the deep interior through the lunar crust is no more than about a third of that for the earth. Thus thermally driven processes cannot be so important as for the earth.
The moon's mantle, nearly 800 to 1000 kilometers deep under the lunar crust, is uniformly structured. Most of it may be pyroxene and olivine, minerals containing silicon, oxygen, calcium, magnesium, and iron. The seismic data reinforce the view that the moon's core is unlike earth's metallic core. Probably the lunar core consists of partly molten silicates, with a small metallic center. At present scientists can neither rule out the existence of a small iron core nor prove that one does not exist.
Only a few decades ago the moon was a light in the sky that, even though near, was still part of the remote cosmos. Now it is a place that has been visited by human beings and studied to such a close extent that it seems no longer to be a cosmic body. What is its future role in the affairs of man? There are proposals to establish permanent bases on the moon for astronomical observatories, mining operations, ore refining, or manufacturing; and it is not impossible that moon the moon may become the departure station for manned exploration of the solar system. But from any point of view it is no longer a strange aand distant world.
