A History of the Terrestrial Planets

Perhaps it seems presumptuous to consider the interiors of the other planets when man has yet penetrated by drilling and mining something less than 5 kilometers into his own. However, geophysicists have made a science out of determining what is beneath their feet, and the amount of information that can be obtained by geophysical methods in advance of drilling is quite spectacular. Indeed, by these indirect methods we have learned a good deal about the very deep inaccessible interior of the earth. It is only natural, then, that geophysicists are now talking about the interiors of the other planets, and with-I might add-more assurance in some respects than they have about the interior of the earth.