月度1.2.7月球的形成

sallylulu · 发表于 2011-5-19 13:40:39

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The Formation of the Moon
Any successful theory must account for everything we know about the Moon now, as well as make predictions about future observations. There are three theories about how the moon came to be in place:
that the moon came out of the crust of the Earth
that the moon was captured by the Earth
that the Earth and moon formed together out of the primordial nebula
By whatever means it came to be in place, as the Moon finished forming, about 4 billion years ago, the surface continued to be bombarded(遭受炮轰） by the remains of planetary material (planetismals) available nearby. This period is the same for all planets, and is called the Period of Late, Heavy Bombardment. During this time the moon warmed, separated into a core and mantle, and experienced volcanism(火山作用）. There is abundant evidence of volcanic plains from this time period. Toward the end of the Period of Late, Heavy Bombardment scientists think that the Moon experienced a series of significant collisions which formed what we know today as the lunar Maria. The impact basins formed by the collisions flooded with darker material from the interior of the Moon, forming smoother, darker plains.
Because of its small size, the Moon would have cooled very rapidly compared with the Earth. When the Period of Bombardment ceased, the Moon cooled completely to the form we see today. Surface activity in the form of plate tectonics and other forms of surface activity ceased once the Moon cooled. Even the interior of the Moon seems to have cooled to the form of inactivity today.

参考英文阅读：
In some ways, it might not seen a complicated question, where did the moon come from? One would assume it formed as did the other solar system bodies and ended up in orbit around the Earth. But it is not as simple as all that, and astronomers have argued several theories about lunar origins for years. The fission theory states that the moon broke from a rapidly spinning "proto-earth." If this happened after the Earth differentiated (dense materials sunk inward, less dense floated to top) it would explain why the moon is less dense than Earth. In fact, the moon has a very low iron content and this fits in perfectly with this theory. What killed this theory was analysis of the lunar rocks. They differ chemically from the crustal rocks of Earth. Another blow to this theory was that if the proto-earth was spinning fast enough to "spit" out the moon, there would be more angular momentum in the Earth-Moon system than is observed today. The next theory to be offered up was the condensation theory which suggested that the Earth and Moon condensed from the same cloud of material. This theory died quickly because the Earth and Moon have quite different densities and compositions. The Moon is poor in volatile materials such as water, which is abundant on the Earth. The capture theory suggests that the Moon formed elsewhere and was later captured by the Earth. This would explain the different densities and compositions, but leads to some tough questions with no satisfactory answers. There would have to be a complex set of circumstances for Earth to be able to capture a body as large as the Moon. It is also believed that it would take such strong gravitational forces by the Earth to capture the Moon, that it would likely tear the Moon apart. The most widely supported theory as to the origin of the Moon is the large impact theory. If a very large body (such as Mars size) struck the Earth, a huge amount of eject would be thrown up and into orbit around the Earth. It is possible the Moon could have formed from this debris. This material would be a combination of debris from both Earth and the impacting body. This theory explains the differences in density and composition.

sallylulu · 发表于 2011-5-19 13:42:36

拷到的童鞋帮忙看看哇~~

[考古] 月度1.2.7月球的形成

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