From interstellar gas to the Earth-Moon system

Autor: A. G. W. Cameron
Rok vydání: 2001
Předmět:
Zdroj: Meteoritics & Planetary Science. 36:9-22
ISSN: 1945-5100
1086-9379
DOI: 10.1111/j.1945-5100.2001.tb01806.x
Popis: — This paper reports the current status of my smoothed particle hydrodynamic (SPH) simulations of the formation of the Moon. Since the Moon has recently been found to have been formed approximately 50 Ma after the solar nebula itself was formed, I have placed the lunar formation problem in the entire context of the formation and early evolution of the solar nebula. This set of processes remains controversial, and I have outlined what I believe to be the essential physical processes involved. These start with the formation of short-lived (now extinct) radioactive nuclides in a massive supernova. Then follows the probable role of the supernova ejecta in triggering the collapse of a core in a molecular cloud to form the solar nebula, and the injection of the radioactivities into the collapsing cloud core. Most of the solar nebula dissipates to form the Sun, and what remains becomes relatively quiescent. Gas drag acting on interstellar grains and the dustballs formed from them, due both to vertical descent to midplane and inward spiralling in midplane, quickly causes growth of the solid materials to form planetesimals. When these bodies reach the kilometer size range and beyond, gravitational forces dominate the accumulation process. The accumulation of the Earth requires of the order of 108 years. About half-way through that process the giant impact occurs with the next largest accumulating body near the protoearth. I have been simulating the giant impact using SPH with 100 000 particles. The simulations of three of these runs are depicted in detail with a series of color images. It is shown that conventional accumulation simulations that assume Keplerian orbits and that merge bodies upon collision are misleading because they cannot take account of tidal stripping nor of loss and gain of particles during the accumulation. In addition, the large rotational flattening of the protoearth renders the orbital motions nonkeplerian. The simulations that are shown in detail have been followed for just over a week of real time, and in that time the largest accumulating clump has reached about half or more of the mass of the Moon and additional clumps have accumulated into bodies in the range of 1 to 20% of a lunar mass. It is important to note that although these runs have given very promising results, the parameter space that could plausibly be associated with the giant impact is not yet adequately explored.
Databáze: OpenAIRE
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