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BloGitud : The Origin of The Moon

To explain the origin of the Moon, the most likely hypothesis is that it’s a result of a collision of Earth with a celestial body which had the size of Mars. According to two researchers from the University of Santa Cruz, this collision would have caused another moon , later, between the young moon and an orbiting companion. This would explain the appearance of the dark side of the moon.
Early in the Hadean, that is to say there are more than 4 billion years ago , a celestial body with the size of Mars, named after Theia, is colliding with the Earth. The iron core of Theia would have merged with that of the Earth but part of the mantle torn by a tangential impact, mixed with that of Theia, although at a very high temperature and form a debris disk, would eventually accreting to give the moon. It was explained this way why the moon is low in water and volatile elements, while having an isotopic composition reminiscent of the mantle of the Earth.


Numerical simulations on the formation of the planets are in favor of this hypothesis, which seems more likely that formation of the satellite away from Earth, followed by a subsequent capture.
But according to other simulations by Erik Asphaug and Martin Jutzi, University of California at Santa Cruz, other important events would also be passed shortly after the formation of the Moon across the evolution of the solar system of course. If the scenario proposed by the two researchers in a recent article in Nature (link given below) is correct, we would have the key to a mystery dating back to the observations of the Soviet probe Luna 3 in 1959. The pictures she showed, in fact, provided a striking contrast between the appearance of the dark side of the moon and his face, hard to explain.

Several hypotheses have been proposed since then. The last is the idea, supported by numerical simulations, that the Moon was not the only body in the vicinity of the accreting Earth.
A second Moon to Earth
Just as there is an asteroid that can be described as a trojan in the Lagrangian points of the Earth-sun, a small body with about 3% of the mass of the Moon would have formed from material common to Earth and Theia at the site of a Lagrange point of Earth-Moon system.
Still unstable, the orbit of the Trojan little body would have to collide after 100 million years with the dark side of the moon today. The collision would have been “soft”, only 8600 km / h. As a result, the small celestial body would have crashed by deforming by taking a little look like a pancake, covering one lunar hemisphere. This would cause the virtual absence of sea on the lunar far side of the moon‘s topography and higher.


One way to test this theory in the coming years there may be. In September, a NASA mission called the Grail should start towards Moon. Its purpose is to make gravity measurements of thin Moon. Solving what is called an inverse problem in geophysics, planetary scientists can deduce from the knowledge of the gravitational field of the moon a number of characteristics of its crust and its mantle. It is possible that we discover that they are exactly what one would expect in the scenario and Asphaug Jutzi.
We would then at least two moons were orbiting the Earth at some point in its history.

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