Formation of the terrestrial planets and the Moon

Computer simulations of the evolution of orbits of planetesimals were made for the feeding zone of the terrestrial planets (Ipatov, 2019). Based on our calculations, we drew conclusions on the process of accumulation of the terrestrial planets. The inner layers of each of the terrestrial planets were mainly formed from the material located in the vicinity of the orbit of a certain planet. The outer layers of the Earth and Venus could accumulate the same material for these two planets from different parts of the feeding zone of the terrestrial planets. The Earth and Venus could acquire more than a half of their masses in 5 Myr. A relatively rapid growth of the bulk of the Martian mass can be explained by the formation of Mars' embryo (the mass of which is several times less than that of Mars) due to contraction of a rarefied condensation. When planetesimals fell onto the embryos of the terrestrial planets from the feeding zone of Jupiter and Saturn, these embryos had not yet acquired the current masses of the planets, and the material of this zone (including water and volatiles) could be accumulated in the inner layers of the terrestrial planets (Marov, Ipatov, 2018). Embryos of the Moon and the Earth may have formed as a result of contraction of a common parental rarefied condensation with a mass not less than 0.01 of the Earth mass (Ipatov, 2018). The angular momentum of this condensation required for such contraction could largely be acquired in a collision of two rarefied condensations producing the parental condensation. For the current lunar iron abundance to be reproduced, the amount of matter ejected from the Earth embryo and infalling onto the Moon embryo should have been an order of magnitude larger than the sum of the overall mass of planetesimals infalling directly on the Moon embryo and the initial mass of the Moon embryo, which had formed from the parental condensation, if the original embryo had the same iron abundance as the planetesimals. The greater part of matter incorporated into the Moon embryo could be ejected from the Earth in its multiple collisions with planetesimals (and smaller bodies). References: Ipatov S. I., Solar System Research 52, 401-416 (2018), DOI: 10.1134/S0038094618050040. Ipatov S. I., Solar System Research 53, 433-2623 (2019), DOI: 10.1134/S0038094619050046. Marov M. Ya., Ipatov S.I., Solar System Research 52, 392-400 (2018), DOI: 10.1134/S0038094618050052.