无月叁阅读JJ补充一个冥王星那篇

lilyzora

我前天去考做到20题，给了我一篇超级恐怖的阅读……就是这篇将轨道什么的migration的文章 三段但jj上原本就很少也没有什么题，所以就很慌啊……20道之后就做的不太好了。这篇文章中有许多the more...the more...类型的句子，大家也都知道GMAT最喜欢在此处作文章，但此类句子几乎贯穿了文章的第二和第三段！！！看得晕死啊，我觉得以后遇到这种，要写在草稿纸上，标个箭头什么的，我这次就彻底亏了呀~~
废话不说了，不甘心的我找到了维基百科上的资料，我记得文中第三段讲到了mechanism2个，维基上有，还有scattering这个单词哦，绝对是一道题目里面的！！
给个链接：http://en.wikipedia.org/wiki/Planetary_migration

Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis. The generally accepted theory of planet formation from a protoplanetary disk predicts such planets cannot form so close to their stars, as there is insufficient mass at such small radii and the temperature is too high to allow the formation of rocky or icy planetesimals. It has also become clear that terrestrial-mass planets may be subject to rapid inward migration if they form while the gas disk is still present. This may affect the formation of the cores of the giant planets (which have masses of the order of 10 Earth masses), if those planets form via the core accretion mechanism. Planetary migration is the most likely explanation for hot Jupiters, extrasolar planets with jovian masses and orbits of only a few days.

Type I migration
Terrestrial mass planets drive spiral density waves in the surrounding gas or planetesimal disk. An imbalance occurs in the strength of the interaction with the spirals inside and outside the planet's orbit. In most cases, the outer wave exerts a somewhat greater torque on the planet than the interior wave. This causes the planet to lose angular momentum and the planet then migrates inwards on timescales that are short relative to the million-year lifetime of the disk.
Type II migrationPlanets of more than about 10 Earth masses clear a gap in the disk, ending Type I migration. However, material continues to enter the gap on the timescale of the larger accretion disk, moving the planet and gap inward on the accretion timescale of the disk. This is presumably how 'hot Jupiters' form.
Gravitational scatteringAnother possible mechanism that may move planets over large orbital radii is gravitational scattering by larger planets. In the case of our solar system, Uranus and Neptune may have been gravitationally scattered in close encounters with Jupiter and/or Saturn.^[1] Planetesimals that were present in the early formation of the solar system called oligarchs are much smaller than Uranus and Neptune and so are likely to have been scattered much further out and be roaming the space between the Kuiper belt and the Oort cloud. Sedna may be the first known example of such oligarch planets. Even smaller objects would have been scattered even further out to become the Oort cloud.

总之首先希望大家运气好一点不要遇到这篇啦，万一万一遇到，不要慌！要淡定~~
祝大家好运！也希望自己再战的时候能更加顺利！