Fragments of the Moon Formation: Geophysical Consequences of the Giant Impact

Abstract

The most likely scenario for the Moon formation is given by calculations of the Giant Impact (GI) of the ProtoEarth with a protoplanet with a mass close to Mars. During the GI, gases and silicate fragments with a total mass of about 55 to 70% of the mass of the Moon go to infinity, but infinity for the runaway particles is infinity in the terrestrial reference frame. In the Solar System, these fragments go into finite orbits with periods both less and more than a year. The most important feature of their orbits is that they all pass through the region of the Earth’s orbit where the GI occurred. A concentrated gas–dust flow was formed there with a fading intensity; it existed for about a million years. Numerically solving the three-body problem yields numerous fragment trajectories. The probabilities of fragments colliding with the Earth and the Moon are estimated as a function of time after the GI. The scenario of fragments falling into the L4 and L5 triangular Lagrange points and the trajectories of their evolution is considered. The most important geophysical consequence of these collisions was the formation of the terrestrial atmosphere and ocean from the concentrated gas–dust flow.