Origin of the Moon

Abstract

Recent geological discoveries suggest that the moon originated during a catastrophic event, at a date near −3.5 b.y. It is here suggested that the event was the fission of the proto-earth to form the moon. It is shown that fission would be expected to lead, not to a pair of corotating bodies, as generally assumed, but to two bodies each rotating with approximately the angular velocity of the critical Jacobi ellipsoid, and revolving in a period about double the period of rotation. This fission process would conserve angular momentum and would approximately conserve energy and vorticity. It would be followed immediately by a period of severe energy dissipation, in which the two bodies would be brought to corotation. During this period, both bodies would be subjected to heating sufficient to volatilize their constituents. During this period, it is suggested that the system would resemble a contact binary. In particular, it is suggested that there would be a large loss of matter and of angular momentum from the proto-moon. In this way is explained the small mass of the moon relative to the mass of the earth, the deficiency of the total angular momentum of the present earth-moon system, and the evidence of differential volatilization in the early history of the earth.