f705 J-M Souriau: On the Dynamics of the Solar System (p5)
...The idea of a lunar origin due to a collision between Earth and another planet is not new. Recently, highly suggestive numerical simulations have brought this hypothesis to the forefront of scientific media, accompanied by stunning artist's renderings. I suggest enriching this hypothetical scenario as follows:
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A "primitive Earth" would initially have followed a more balanced trajectory, in accordance with a general golden ratio law. It may already have possessed an atmosphere. It might even have harbored primitive life (if the collision occurred during the early stages of the solar system; less likely if it happened more recently).
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A collision, or a component of the perturbation, conjectured by Claire, would then involve a very massive planet, rich in metallic elements (iron).
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The collision would produce an enormous "splash." Earth's crust would be torn apart. Fragments of the crust and pieces of Earth's magma would be ejected. These materials—these ejecta—would form the young Moon, and possibly a group of asteroids and future satellites of other planets.
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Some of these ejected objects could subsequently be captured by large planets, forming non-resonant satellites, while resonant satellites would be considered "origin satellites."
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The components causing the perturbation would disrupt "Jupiter's ring," these components becoming the future comets.
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Some of these components would form the asteroid belt, joining a non-resonant orbit.
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Part of the mass of the impacting body would become incorporated into Earth, forming its iron core.
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Earth would then acquire a "non-resonant" orbit. See the corresponding figure based on the golden ratio, shown earlier.
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During the collision with this object X (to be defined), Earth's magma would erupt and cover a significant portion of the original crust:
Fig.13 (p020): The impact has just occurred. A mixture of surface magma and debris from Earth's crust is ejected. Since the collision was not perfectly frontal, an ejecta (the future Moon) is also thrown outward. The magma falls back onto Earth in a corona-like pattern.
...We cannot assume anything about the state of this primitive Earth before impact, if it indeed occurred. It may already have released its atmosphere, possibly harbored primitive life. And perhaps—why not?—if the catastrophe happened late enough, even a highly organized life, or even a civilization, severely damaged by this cosmic accident.
...The kinetic energy from the impact heats the magma, triggering intense volcanism, which in turn leads to the reformation of a "secondary primitive atmosphere."
Fig.14 (p021): After the collision. The Moon begins to form.
Earth has regained its sphericity.
...The magma is exposed to the surface. As it solidifies, it forms the oceanic crust, thinner in thickness, with the major scar being the Pacific Ocean.
Fig.15: The debris have either been scattered throughout the solar system or absorbed. The Moon has taken on its spherical shape, retaining a bulge—a sign of its initial status as an ejecta. Earth's magma solidifies. The primitive atmosphere (if it had one) has either been dispersed or severely disturbed. Intense volcanism, driven by renewed convection, rebuilds it through volcanic activity.
...The heat generated by the impact must be dissipated. This energy input would restart convective currents. Life, if it existed before the collision and was not entirely destroyed by the catastrophe, would resume, however painfully. Evolution might have accelerated due to the survival of primitive organisms despite the extremely harsh conditions following the impact. The primitive continent, a fossil of Earth's original crust, would begin to fragment (continental drift, absent on other solid planets in the solar system).
...It is commonly assumed that lunar maria are lava flows resulting from asteroid impacts. But why, under these conditions, are they located facing Earth? Why, at a time when the Moon still rotated on its axis, were these strong impacts not uniformly distributed across the satellite?
...If these impacts occurred after the Moon had oriented itself toward Earth due to its bulge, they would have been weaker, as Earth would have shielded the Moon from such impacts, while simultaneously deflecting objects that escaped Earth's gravity and then struck the Moon. Conversely, the far side of the Moon is heavily cratered, as incoming objects benefited from Earth's gravitational pull. Another interpretation: these maria could represent the "wound" on the Moon's side. The Moon might have formed from two components: a fragment of Earth's crust and some denser magma. When this droplet assumed a spherical shape, the denser part, facing Earth, would have formed the bulge.
...However, there exists another competing hypothesis, which I acknowledge is very strong, as noted by Souriau: Initially, the Moon rotated on its axis. Then it suffered a colossal impact corresponding to a single dense object, which—due to tidal forces, like the Shoemaker-Levy comet—had already fragmented before impact. These fragments, descending at extremely high speed, plunged into the young Moon's surface, piercing its crust and causing magma to erupt. Thus, the maria were formed. All these maria would have formed simultaneously, during a single multiple impact. But these fragments could not freely flow toward the Moon's center, which by then was already too viscous, and instead became embedded beneath the crust, forming "mascons" (mass concentrations), subcrustal masses later detected. Thus weighted, the Moon acquired its bulge and ceased rotating.
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