It is widely known that the side of the moon that faces us has a particularly large number of dark patches, which resemble seas of liquid, hence, "maria". It is strange, though, that the far side of the moon has a great lack of these features. Why does the far side of the moon have so few maria? If they maria formed due to impacts, is there some reason that the far side would have less collisions?
To answer to this question one must first give some explanation into Earth-Moon system and its origin.
Since Earth’s gravitational field is much larger than the Moon’s, synchronous coupling has already occurred for the Moon’s rotational and revolutional periods. This explains why the same side of the Moon is always tilted towards the Earth. Such a resonance is thought to have become entrenched during the early history of the Solar System when the planets were hotter and softer.
Under tidal actions of the Earth the more dense components of the Moon’s interior moved within the spherical body. By the time the resonance was reached the Moon’s mass distribution had been shifted along an axis pointing towards the Earth and the molten rocks had cooled.
More evidence to this scenario is obtained by comparing the appearance of the facing and opposite surfaces of the Moon. The facing hemisphere has large number of seas that are solidified lava flows whereas the reverse side has none. The relatively low-density crust is thinner on the side facing the Earth and has thus been ruptured by hotter material from Moon’s interior at certain stages of the Moon’s history. The thicker crust on the reverse face has prevented this happening there.
The near side of the moon has a thinner crust on average than the far side, and contains a larger amount of heat producing elements below the crust (causing the near side to be more volcanically active). The uneven crust and distribution of heat producing elements can be explained by the tidal lock of the moon: One side of the moon always feels a larger pull from Earth's gravity than the other.
Take a good look at the surface of the moom during the next fuul moon. You can see some of its large surface features, especially if you use binoculars or a small telescope. You will see dark-colored maria (MAR ee uh) and lighter-colored highland areas. Galileo first named the dark-colored regions maria, the Latin word for seas. They reminded him of oceans. Maria probably formed when lava flows from the Moon's surface. These depressions may have formed early in te Moon'd history. Collected during Apollo missions and then analyzed in labratories on Earth, rocks from the maria are about 3.2 billion to 3.7 billion years old. They are the youngest rocks found on the Moon thus far.
protected by Qmechanic♦ Apr 29 '13 at 15:20
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