【雙語閱讀】Lunacy and astronomy 天文也瘋狂

TO BE parochial on an astronomical scale sounds like a tall order. Yet people manage it all the time. When they think about the possibility of life in other parts of the universe, they think of it happening on planets. But this is simply local prejudice. Moons, which Earthlings tend to see merely as adornments to the night sky, are just as good a place to look for life as planets are, perhaps even better. Which is why astronomers are trying to spot the moons of planets around other stars (see article). And life is just a part of it. To anyone not hung up on hierarchies of who-orbits-whom, moons are in all manner of ways more various and more intriguing than planets.要說在廣闊天文學領域存在著狹隘理念聽起來不可思議，但人們還真一直都有這種想法。每當談及地外哪裡可能有生命的存在時，人們討論的範圍都是都是在行星之間。而衛星僅僅被視為夜空中的裝飾。這純粹是種偏見，其實在這些衛星上和行星一樣，都有存在生命的可能，甚至在衛星上的可能性還更高。為此，天文學家正努力在星空中尋找行星衛星，也順帶尋找地外生命。有些人則不糾結於行星、衛星誰繞著誰轉的主次關係，對他們來說衛星比行星更多樣，也更具吸引力。It is true that moons are, on average, small. But big moons can be larger than small planets. And what they lack in size moons make up for in variety and activity. Their surfaces range from the stark cratering of Earth』s moon through the cantaloupe-skin of Triton, which circles Neptune, to the cue-ball-smooth ice of Europa and the lurid leprous sulphur of Io, both companions of Jupiter. And though the three rocky planets that are not the Earth—Mercury, Venus and Mars—appear to be geologically quiescent, that is not true of many moons. Spacecraft passing both Triton and Enceladus, a satellite of Saturn, have seen geysers that dwarf those of Iceland or Yellowstone, and the volcanoes of Io are in constant tumult.總的來說，衛星體積都比較小，但也有也比小行星體積更大的衛星存在。小體積的衛星種類更豐富，運動更活躍。它們表面有的千瘡百孔，比如月球；有的像是瓜皮，比如海衛一；有的則布滿跟溜溜球一樣光滑的冰，比如木衛二；更有甚者表面鋪滿硫磺，看上去就像得了麻風病一樣恐怖，比如木衛一。九大行星中除地球外有三個石質行星——水星、金星和火星，他們在地質活動方面都表現平靜。但對多數衛星來說則恰恰相反，飛行探測器經過海衛一和土衛二時發現，這兩顆行星上的地熱噴泉要比冰島和黃石公園的同類大得多；而海衛二上的火山更是日以繼夜的活動著。Planets do have an edge when it comes to atmospheres. Venus, Earth and Mars all boast thick enough envelopes of gas to have weather; among the moons only Saturn』s Titan has anything to speak of in that department. But in the matter of oceans—widely seen as a near-necessity for life—the moons do well. Venus and Mars long ago misplaced any seas they may once have had, leaving Earth the only oceanic planet. Earth』s oceans, though, are smaller than those beneath the icy crust of Europa—and Europa』s siblings Callisto and Ganymede may well have subsurface oceans, too, as may Triton. Titan, meanwhile, has rivers, clouds, rains and lakes of methane.行星的邊緣都有大氣層：比如金星、地球和火星都孕育了足以產生多樣天氣的大氣層。而在衛星中，只有土衛六有類似的大氣。但衛星上也存在萬物賴以生存的海洋。金星和火星上面的海洋似乎在很久以前放錯了地方至今不復存在，地球是目前唯一有海洋的行星。但是要知道，木衛一的冰殼面積比我們地球的海洋還要廣闊，而木衛三和木衛四表面下面也可能存在海洋；同樣，在海衛一、土衛六表面下野可能有液態甲烷組成的河流、雲層和降雨。In other star systems, moons have many advantages as abodes for life. One of the discoveries that has come with the ability to detect planets around other stars is that planetary systems are knockabout places in their early years. A lot of small planets get flung out of their orbits into outer darkness. This is less likely to happen to such a body if it is the moon of a large planet, so moons may survive preferentially. And moons can be hospitable where planets are not. An Earth-sized planet too close to its star will end up with one face permanently illuminated and one eternally dark. But a moon going around a large planet in such an orbit is saved from such a fate; as it orbits its parent orbiting the star all of its surface will, from time to time, be bathed in the star』s welcome light.在其它星系系統中，衛星們有許多作為生命住所的優勢。依靠進步的科技，在探測外星系行星時，人們發現其實太陽系早期其實是一個大雜燴。在宇宙形成初期，許多小行星都脫離軌道而被拋向無盡的黑暗裡。但許多依附了較大行星的衛星則不會被拋走，而得以倖存。衛星比行星更加友好。地球大小的行星如果太靠近恆星則會使得一面永久光明、另一面永久黑暗。但衛星由於繞行星運轉得以避免這種厄運。因為衛星的母星在繞著恆星周轉，這樣的話，衛星的整個表面都可以按周期沐浴到太陽光了。In the heavens as it is not on Earth天空中和地球上可不一樣Moons orbiting planets far away from their stars may also be more hospitable to life than Earth-sized planets would be in similar orbits. A big planet gives off heat. That warms its moons. And further warmth is available from tides. The tides Earth』s moon raises on its parent can be powerful things. Those raised by planets on their moons are more powerful still, since a planet is bigger, and thus has stronger gravity, than its moons. It is the heat produced by constant tidal kneading of their interiors that makes Enceladus spout geysers and Io volcanoes when planets of their size would sit inert.遠離恆星的行星衛星在相似軌道下比起和地球體積差不多的行星更加適合生命生長。大行星會散發熱量，給它的衛星取暖，而潮汐也能進一步帶來熱能，地球上的潮汐由月球引起，力量強大。而由行星引力導致的衛星潮汐則會更加可觀，這也因為行星比衛星體積更大，引力更強。持續的潮汐使得星體內部得到運動，就像土衛二的噴泉和海衛一的火山就是由此產生，本來這些星體的活性還是比較平靜的。No one can say whether life is more likely on moons than on planets—but astronomy stands ready to answer such questions over the coming decades. Humans assume that the way things are on Earth is the way things must be. Science is there to help them widen those narrow minds.目前，還沒人能夠確定衛星比行星更有可能存在生命，但天文學的進步將會在未來給出這個問題的答案。人類總假設地球的生命模式是惟一的。但科學正是為了去除偏見，增廣人類的視野。
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