The origin of the Moon

All the satellites of the Solar System are small: from 25 to thousands of times smaller than their relative planets. The only exceptions are the Earth-Moon and the Pluto-Charon systems; our Moon has a diameter that is only 1/3 the Earth’s diameter. This implies that maybe the processes that brought to the formation of the Moon were different from those of the other satellites. To date, four hypotheses have been advanced regarding the origin of the Moon:
1) The Moon might be a fragment that separated from the Earth shortly after its formation (fission hypothesis);
2) After having being formed in some part of the Solar System, the Moon might have been captured by Earth’s gravity (capture hypothesis);
3) The Moon might have formed from dust and debris orbiting around Earth (accretion hypothesis);
4) The Moon might be the result of the aggregation of many planetesimals orbiting around our planet, resulting from the collision of the Earth with a planetary body the size of Mars (collision hypothesis).
Currently, the most favoured hypothesis seems the last one. After the gigantic “slap”, the Moon must have formed as a result of the mutual gravitational attraction of the remains of the collision, bringing about further re-fusion and differentiation of the layers and matter and a consequent cooling. During this process, the surface must have been subjected to an intense meteorite bombardment that transformed the rocks on the surface into a layer of dust and debris. Subsequently, the internal heating must have caused the eruption of matter, creating the basalt lava flows called maria, and the other characteristic tectonic and volcanic activities that are present on the surface.
This sequence of events would explain why the Moon is very similar to the Earth as far as some characteristics are concerned, but not respect to others that it might have “inherited” from the body that collided with our planet.

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