冰冷的世界
火热的研究（英文原文） |
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作为一个科学家,我经常感到自己就像一个高科技侦探，努力尝试揭开就连阿加沙·克里斯蒂都会畏缩不前的迷题。然而，面对冥王星时，我和同事们感到就像圣诞节前孩子们试图打开礼物时那样——你几乎难以想象到里面是什么。似乎好戏总在后面。 冥王星和卡戎，这对双行星，总是蹒跚地游弋于太阳系的边缘。而在过去的十年里，我们对于它们的了解却有了爆炸性进展。想想看吧，从1978年以来，我们知道了冥王星比我们估计的要小的多，而且也含有更多的岩石成分。在天文的时间尺度上，它的轨道是混沌的。冥王星被外来的、强挥发性的氮、甲烷和一氧化碳雪层所覆盖，而卡戎却裹在杂质水冰中。冥王星的表面不寻常地变化多端，其极冠、热点等各类特征与所有内行星有着明显差异。它那胀大的大气极快地逃逸出去, 以至于其所有的地表特征将在地质时期内消失殆尽。冥王星是太阳系中唯一的真正的双行星(卡戎的半径正好是冥王星的一半)；因而就像一对紧密双星一般，冥王星脆弱的大气一部分很可能溢出到卡戎附近的轨道上。冥王星更可能是一个残余的微行星，只不过是1000多个冰质矮微行星中最大的一个——而现在看来，它们似乎是我们太阳系所产出的行星体中最多的一族。透过迷雾，我们才开始感激冥王星——我们最后留下的世界——也许比木卫一、氦卫一甚至火星更为复杂。冥王星是天王星、海王星、柯伊伯带彗星形成时代的一个遗迹，也同时是一个叛异者。而且，我们凭借现代的技术水平能够到达它！我在儿童时代看到月球成了一个实实在在的地方，接着在青春期是火星，而后在大学和研究院时是木星，土星和荒凉的天王星和海王星变成了实景。现在对我来说，同许多年轻些的行星科学家一样，这些似乎就像我父亲的奥兹莫比尔汽车变速器一般。是的，冥王星是我们的！这颗不大的行星将是我们行星探索一代想象力和问题解决的金字塔尖和珠穆朗玛峰。 冥王星（或更准确的说，冥王星－卡戎）也是最后的“天文学家的行星”。它也将使我们最终能够得知徘徊者号（月球探测卫星）、水手号、海盗号、和旅行者号所给我们上的难得几课是否充分。它也将使我们得知，我们能否在先前的探索的指引之下，通过望远镜和空间天文台真正认识一个行星。它也将使我们得知，我们是否已有足够深厚和多样的背景，能够真正意义上想象到我们即将用望远镜指向的其他太阳系。 更使我感到惊讶的是，它正像是一面镜子。有人把它看作是探索的前沿,一些人看到了唯一的双行星。有人看出了土卫六和海卫一的类似体，而另一些人却看到了柯伊伯带最大的冰矮星。一些人看到了研究大气流体动力学逃逸的物理机制，而另一些人却看到了地月系最好的近似物和创造地球和月球的巨大原始冲击。每个人都看到了些不同，而它们又全是正确的。 很久以前，有人说：“凡季皆有其时”。让我们拓宽我们的视野，探索这个新的双星世界并来看一看，就像我们曾经所做的——我们的后代是否能够发现那个有一点点冰和矿物，经典低温物理环境之下和一个千倍于我们的时间跨度之下的世界究竟是怎么样的。
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译自 The Planetary Society,2000 |
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Grazing Encounter Between Two Spiral Galaxies |
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As a scientist, I usually feel like a high-tech detective, trying to unravel mysteries even Agatha Christie would cringe at. However, with Pluto, I and many of my colleagues feel like kids at Hanukkah (or Christmas), trying to unwrap presents our siblings hardly imagined could ever (really) be for us. It's as if the best was saved for last. In the last decade, there has been an incredible explosion of knowledge about the little binary planet Pluto-Charon, which is poised on the ragged edge of the planetary system. Imagine, since 1978 we have learned that Pluto is smaller than ever expected, but also rockier. That Pluto's orbit is chaotic over astronomical timescales. That Pluto is covered with exotic, super-volatile snows of nitrogen (N2), methane (CH4) and carbon monoxide (CO), but its sole satellite, Charon, is encased in run-of-the-mill water ices. That Pluto's surface seems to be unusually diverse, with polar caps, hot spots, and markings as distinct as any on the inner planets. That Pluto's puffy, distended atmosphere is escaping from it so fast that surface features can "escape away" over geologic time. That Pluto is the only true double planet in the solar system (Charon is exactly half Pluto's diameter). That some of Pluto's tenuous upper atmosphere probably spills over into orbit about Charon, as if it were a tightly orbiting binary star. That Pluto's atmosphere comes and goes with each orbit, like some giant, planetary-scale comet with four seasons that make any others in the solar system, save Triton' s, look wan and wimpy by comparison. And that Pluto is very likely a leftover mini-planet, the largest of the 1,000-plus ice dwarf mini-planets, which seem now to make up the most populous class of planetary bodies our solar system has produced. Through the mists that hindsight clears, we are now coming to appreciate that Pluto, the world we left till last, may be more complex than Io, Triton and even Mars. Time, sweat-equity and the eye-opening explorations of Voyager have revealed that Pluto is a relic, and a reporter, and a renegade from the era of formation of Neptune, Uranus and the Kuiper comet disk. And now we are capable of reaching it. I saw the Moon become a real place in my childhood, followed by Mars in my adolescence. Jupiter, Saturn, and the wild ones, Uranus and Neptune, became places when I was in college and graduate school. And yet to me, like many other younger planetary scientists, all these seem rather like My Father's Oldsmobile. Pluto is ours! It's the little planet that could, the measure of our imagination and resolve, the top of the pyramid, the Everest for our planetary generation. Pluto (or, more properly, Pluto-Charon) is also the last "astronomer's planet." It is the one on which we will finally know if the hard-won lessons of the Rangers, the Mariners, the Vikings and the Voyagers were sufficient. It is the world on which we will learn whether we can, after all our early explorations, get a planet right from our telescopes and space-based observatories. It is the world on which we will learn whether we have gained a sufficiently deep and diverse background to imagine (in any real sense) the diverse worlds of other solar systems that we will soon plumb by telescope. What amazes me about Pluto-Charon is that it is a mirror. Some look, and see it as the frontier of exploration. Others see a unique double planet. Some see an analogue to Titan and Triton, while others see the largest ice dwarf of the Kuiper disk. Some see the chance to study the physics of hydrodynamically escaping atmospheres (read: comets on a planetary scale), but others see the best analogy to the Earth-Moon system and the ancient, giant impact that created our Terra and Luna. Each sees something different, but they are all correct. Long ago it was written: There is a time for every season under heaven. Let us extend our grasp, explore this strange new binary world and see if our children can discover, as we did ourselves, what Nature can do with a few ices and minerals, a little classical low-temperature physics, and a time span a thousand times our own. |
From The Planetary Society, 1994 |