問題詳情

Europa is the smallest of planet Jupiter's four largest moons and the second moonout from Jupiter. Until 1979, it was just another astronomy textbook statistic. Thencame the close-up images obtained by the exploratory spacecraft Voyager 2, and withindays, Europa was transformed--in our perception, at least--into one of the solar system'smost intriguing worlds. The biggest initial surprise was the ahnost total lack of detail,especially from far away. Even at close range, the only visible features are thin, kinkedbrown lines resembling cracks in an eggshell. And this analogy is not far offthe mark.The surface of Europa is almost pure water ice, but a nearly complete absence ofcraters indicates that Europa's surface ice resembles Earth's Antarctic ice cap. Theeggshell analogy may be quite accurate since the ice could be as little as a few kilometersthick--a tree shell around what is likely a subsurface liquid ocean that, in turn, encasesa rocky core. The interior of Europa has been kept warm over the cons by tidal forcesgenerated by the varying gravitational tugs of the other big moons as they wheel aroundJupiter. The tides on Europa pull and relax in an endless cycle. The resulting internal heatkeeps what would otherwise be ice melted almost to the surface. The cracklike marks onEuropa'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 ofEuropa were obtained, researchers advanced the startling idea that Europa's subsurfaceocean might harbor life. Life processes could have begun when Jupiter was releasing avast store of internal heat. Jupiter's early heat was produced by the compression of thematerial forming the giant planet. Just as the Sun is far less radiant today than the primalSun, 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 liquidright to the surface, making it a crucible for life.
10. What does the passage mainly discuss?
(A) The effect of the tides on Europa's interior
(B) Temperature variations on Jupiter's moons
(C) Discoveries leading to a theory about one of Jupiter's moons
(D) Techniques used by Voyager 2 to obtain close-up images

參考答案

答案：D[無官方正解]
難度：適中0.5
統計：A(0),B(0),C(0),D(0),E(0)

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