moon月亮的形成

纳丁Cat

V2【BY：DALALA】



讲月球形成的，一开始提出3个假说，分裂说，捕获说，共生说，第二段说这三种都不对，如果是分裂，成份应该跟地球相似，如果是捕获，应该整个系统速度更快，否则不可能让月球减速到可以捕获的程度，如果是共生，月球的铁内核应该跟地球相似，所以应该比现在的更大。第三段提出新假说，撞击说，说月球是地球根行星级天体碰撞产生的，这个假说可以解释月球成分铁核和运行速度，同时还强调是有角度的撞击不是直接的对撞(not head to head)



题目问如果是什么什么说，就应该怎么怎么样，如果怎么怎么样了，就可能是什么什么说，定位第二段，不难找到



V4feid1984考古

第一段：讲的就是先。有三个理论，一是fission（就称F吧）什么的，说月亮是地球转着转着甩出去的；二是A（就叫做A吧）开头的一个词，说是月亮和地球是同时由同样的方式形成的；三是capture理论（就叫做C吧），月亮是某个外面的天体飞过来，被地球引力抓住的。
第二段：作者就挨个批评了。主要从两个方面，首先是旋转速度，说要是fission的话，地月旋转速度不知道比现在快多少呢，又说如果是A的话，速度肯定又要慢得多，最后说如果C的话，更没道理，不可能一个外面飞的更快的东东的飞到地月体系就变慢了吧；然后说从物质构成上也不可能滴，说了一个FACT是月球上很少V物质（地球上很多滴），然后又说的如果是C理论的话，月球iron构成的core应该要比现在大得多（大概是这样）。
note：这些证据不是一对一的驳回，而常是一对多的驳回，有两个题是在这儿，我是后来才发现的，唉，因为觉得是JJ，所以作得太快，根本没有去仔细定位，吸取教训啊。
第三段：说最近又有个新理论出现了，比较能解释这些情况，就是collision theory，说月球是撞出来滴~以前有一个星体和地球撞了一下，撞出去的地球的物质就那个星体一起形成了月亮，而那些V物质在碰撞的高温（或者是其他条件下消失了）这个可以解释月球上问什么这个东西少，而由于这两个东西是成一定角度的撞滴，所以形体的速度变慢了
题目：
有四个问题，我不太记得的，我前面题做得太慢了，后面进入状态后只能追着追着做了
总之似乎第三段反而没考点，考点3集中集中在第二段，都是问，这个怎么怎么反驳之类的，大家注意仔细看第二段，比较混乱。分别有3个题，都是细节题针对三种理论。答案应该是：1，月亮与地球spin的关系看出理论1不成立 2，由月亮的core的构成可以判断理论2。3，由月亮的size

V5by 特仑苏爸爸
第一段：有关月球的成因科学家们有三派观点。1）月球是和地球同时形成的 2）月球本是宇宙中游走的天体，被地球俘获。3）月球是地球飞出去的一部分慢慢形成的。
第二段：这三派观点都有说不通的地方让科学家很纠结。1）如果月球是和地球同时形成的，它应该具有和地球类似的组成。但是发现月球表面锌还有别的一个金属的含量很低（不确定高低） 2）如果月球是被地球俘获的话，那地球和月球现在的转动应该更快（不确定高低）3）如果月球是从地球飞出去的部分，他的crater似乎太薄。（MD这些太细了，大家看了别上心，有细节题）
第三段：一个NB的科学家提出了一个新的解释，反正很牛逼，可以解释月球的一些特点。貌似说是地球被一个天体撞了下，撞出去了部分，同时由于撞击产生的高温把部分物质气化了，撞出了特殊的物质，使得月球compostion特别。最后一句记得特清楚，科学家觉得当时是撞偏了，不是head-on撞上地球的。这里问了细节题，所以第二段很重要。
1. 如果俘获论是正确的话，月球对地球而应该体现出什么样的特性。
我选了好像是spin faster 还是slower 大家做的时候自己关注
2.一下哪个点成立可以削弱the objection to the 3者之一的一个理论
选项无非就是根据第二段内容，改了些月球当前的特性。记得有科学家对月球表面元素的分析有错误，月球crater的厚度被低估还是什么的
3. 问了结构，我选了提出了几个存在问题的理论最后提出了一个教完美的理论。（英文不记得了）



一.分裂说。这是最早解释月球起源的一种假设。早在1898年，著名生物学家达尔文的儿子乔治?达尔文就在《太阳系中的潮汐和类似效应》一文中指出，月球本来是地球的一部分，后来由于地球转速太快，把地球上一部分物质抛了出去，这些物质脱离地球后形成了月球，而遗留在地球上的大坑，就是现在的太平洋。这一观点很快就收到了一些人的反对。他们认为，以地球的自转速度是无法将那样大的一块东西抛出去的。再说，如果月球是地球抛出去的，那麽二者的物质成分就应该是一致的。可是通过对“阿波罗12号”飞船从月球上带回来的岩石样本进行化验分析，发现二者相差非常远。
二.俘获说。这种假设认为，月球本来只是太阳系中的一颗小行星，有一次，因为运行到地球附近，被地球的引力所俘获，从此再也没有离开过地球。还有一种接近俘获说的观点认为，地球不断把进入自己轨道的物质吸积到一起，久而久之，吸积的东西越来越多，最终形成了月球。但也有人指出，向月球这样大的星球，地球恐怕没有那麽大的力量能将它俘获。
三.同源说。这一假设认为，地球和月球都是太阳系中浮动的星云nebula，经过旋转和吸积，同时形成星体
celestial body (e.g. planet, satellite, etc.)。在吸积过程中，地球比月球相应要快一点，成为“哥哥”。这一假设也受到了客观存在的挑战。通过对“阿波罗12号”飞船从月球上带回来的岩石样本进行化验分析，人们发现月球要比地球古老得多。有人认为，月球年龄至少应在70亿年左右。
四.大碰撞说。这是近年来关于月球成因的新假设。1986年3月20日，在休士顿约翰逊空间中心召开的月亮和行星讨论会上，美国洛斯阿拉莫斯国家实验室的本兹、斯莱特里和哈佛大学史密斯天体物理中心的卡梅伦共同提出了大碰撞假设。这一假设认为，太阳系演化早期，在星际空间曾形成大量的“星子”planetesimal，星子通过互相碰撞、吸积而长大。星子合并形成一个原始地球，同时也形成了一个相当于地球质量0.14倍的天体。这两个天体在各自演化过程中，分别形成了以铁为主的金属核和由硅酸盐silicate构成的幔和壳。由于这两个天体相距不远，因此相遇的机会就很大。一次偶然的机会，那个小的天体以每秒5千米左右的速度撞向地球。剧烈的碰撞不仅改变了地球的运动状态，使地轴倾斜，而且还使那个小的天体被撞击破裂，硅酸盐壳和幔受热蒸发，膨胀的气体以及大的速度携带大量粉碎了的尘埃飞离地球。这些飞离地球的物质，主要有碰撞体的幔组成，也有少部分地球上的物质，比例大致为0.85:0.15。在撞击体破裂时与幔分离的金属核，因受膨胀飞离的气体所阻而减速，大约在4小时内被吸积到地球上。飞离地球的气体和尘埃，并没有完全脱离地球的引力控制，他们通过相互吸积而结合起来，形成全部熔融的月球，或者是先形成几个分离的小月球，在逐渐吸积形成一个部分熔融meltdown的大月球

七百年后

thx. 正在google这篇

七百年后

和JJ的信息有差异，但方向相同。有兴趣的童鞋可以参考下。

    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.

362445236

我去…前两天要是看了就好了。。。今天考试就这个。。月亮的形成…做蒙了…到第三题突然反应出了文章的真谛…然后…估计就…

alannesta

我也提供一篇背景资料

Several mechanisms have been proposed for the Moon's formation 4.527 ± 0.010 billion years ago,[nb 5] some 30–50 million years after the origin of the Solar System.[11] These include the fission of the Moon from the Earth's crust through centrifugal forces,[12] which would require too great an initial spin of the Earth,[13] the gravitational capture of a pre-formed Moon,[14] which would require an unfeasibly extended atmosphere of the Earth to dissipate the energy of the passing Moon,[13] and the co-formation of the Earth and the Moon together in the primordial accretion disk, which does not explain the depletion of metallic iron in the Moon.[13] These hypotheses also cannot account for the high angular momentum of the Earth–Moon system.[15]
The prevailing hypothesis today is that the Earth–Moon system formed as a result of a giant impact: a Mars-sized body hit the nearly formed proto-Earth, blasting material into orbit around the proto-Earth, which accreted to form the Moon.[16] Giant impacts are thought to have been common in the early Solar System. Computer simulations modelling a giant impact are consistent with measurements of the angular momentum of the Earth–Moon system, and the small size of the lunar core; they also show that most of the Moon came from the impactor, not from the proto-Earth.[17] However, meteorites show that other inner Solar System bodies such as Mars and Vesta have very different oxygen and tungsten isotopic compositions to the Earth, while the Earth and Moon have near-identical isotopic compositions. Post-impact mixing of the vaporized material between the forming Earth and Moon could have equalized their isotopic compositions,[18] although this is debated.[19]
The large amount of energy released in the giant impact event and the subsequent reaccretion of material in Earth orbit would have melted the outer shell of the Earth, forming a magma ocean.[20][21] The newly formed Moon would also have had its own lunar magma ocean; estimates for its depth range from about 500 km to the entire radius of the Moon.[20]
An exoplanetary system has been discovered in which two planets share the same orbit. Such co-orbital planets are thought to be the origin of the impact that produced the Earth-Moon system because models suggest the collision was low-speed[22]

tracy214wxy

顶~！！！！谢谢啦！！！

joyous314

谢谢！

balgirl

俺再提供一个俺在MANHATTAN的在线模考时遇到的题：

Before the age of space exploration, astronomers assumed that the Moon's core was smaller than the Earth’s, in both relative and absolute terms – the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass – but they had no way to verify this. Two sets of data gathered by Lunar Prospector have now given astronomers the ability to determine that the Moon's core accounts for 20 percent of the Moon's radius and for a mere 2 percent of its overall mass.
         First, scientists measured minute, relatively rapid variations in the wavelength of radio signals from Lunar Prospector as the craft moved towards or away from the Earth. Using these variations, scientists accurately determined even slight changes in the craft's velocity while the craft orbited the Moon, changes resulting from inconsistency in the gravitational pull of the Moon on the craft. The data were used to create a "gravity map" of both near and far sides of the Moon, highlighting new details of the distribution of the Moon's internal mass. Scientists thus determined that the Moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the Moon itself by the Moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.
         The size and composition of the Moon's core have serious implications for our understanding of the Moon's origins. If the Moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the Moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps due to a major asteroid impact that could have loosened a chunk of iron, allowing it to form the core around which the Moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.