Passage 3 |
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Title: |
行星的卫星 |
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大致内容 |
土星的两个卫星,一颗(G打头的)17天转一圈,离土星最远,气温黑夜在-140度,科学家认为mantle冻成冰一样硬,但通过伽利略号望远镜发现好像并不完全是。还有一个卫星,因为离土星最近,所以有地质活动,形成了峡谷山脉,最后一段问两者的区别,最大区别(有题)。(最后一题是分别选出两颗卫星的特点,前面两点,后面三点) |
扩展阅读 |
Europa is the smallest of planet Jupiter’s four largest moons and the second moon out from Jupiter. Until 1979, it was just another astronomy textbook statistic. Then came the close-up images obtained by the exploratory spacecraft Voyager 2, and within days, Europa was transformed-in our perception, at least-into one of the solar system’s most intriguing worlds. The biggest initial surprise was the almost total lack of detail, especially from far away. Even at close range, the only visible features are thin, kinked brown lines resembling cracks in an eggshell. And this analogy is not far off the mark. The surface of Europa is almost pure water ice, but a nearly complete absence of craters indicates that Europa’s surface ice resembles Earth’s Antarctic ice cap. The eggshell analogy may be quite accurate since the ice could be as little as a few kilometers thick –a true shell around what is likely a subsurface liquid ocean that, in turn, encases a rocky core. The interior of Europa has been kept warm over the eons by tidal forces generated by the varying gravitational tugs of the other big moons as they wheel around Jupiter. The tides on Europa pull and relax in an endless cycle. The resulting internal heat keeps what would otherwise be ice melted almost to the surface. The cracklike marks on Europa’s icy face appear to be fractures where water or slush oozes from below. Soon after Voyager 2’s encounter with Jupiter in 1979, when the best images of Europa were obtained, researchers advanced the startling idea that Europa’s subsurface ocean might harbor life. Life processes could have begun when Jupiter was releasing a vast store of internal heat. Jupiter’s early heat was produced by the compression of the material forming the giant planet. Just as the Sun is far less radiant today than the primal Sun, so the internal heat generated by Jupiter is minor compared to its former intensity. During this warm phase, some 4.6 billion years ago, Europa’s ocean may have been liquid right to the surface, making it a crucible for life.(老托福2003.10-1) |
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