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If you could hop in a time-travelling spacecraft, go back three billion years and land any place in our solar system, where would you want to end up? Earth, with its barren continents and unbreathable atmosphere? Or Mars, a chillier version its big brother? Wait, what about Venus? 如果你能跳进一台时间旅行机器，穿越三十亿年的时光回到过去并降落在太阳系中的任何位置，你最后会停在哪里？地球？降落在那一片无法呼吸的荒芜大陆？还是火星？一个仅比地球温度稍低的星球？等等，你觉得金星怎么样？
金星（左）是否曾与地球相似？模型表明它很可能是的。图片：维基媒体 Venus has a rep for being a toxic hellscape, but three billion years ago, it may have been the best piece of real estate our solar system had to offer — or at least, a close second to Earth. This hypothesis has been around for years, but it’s gaining traction thanks to climate models developed by researchers at NASA’s Goddard Institute for Space Studies and elsewhere. 金星常被人形容为一个地狱般的场所，但三十亿年前，它可能是我们太阳系提供的最好的一方乐土 - 或者至少环境能接近地球。这个假设已经存在多年，但得益于NASA戈达德太空研究所（NASA’s Goddard Institute for Space Studies）以及其他地方研究员开发的气候模型，人们才逐渐开始关注它。 Those models show that for two billion years, Venus could have had balmy, Earth-like temperatures and liquid water oceans, despite getting dosed with 40 per cent more solar radiation than Earth is today. But it depends on whether the Venus of bygone days spun as slowly as modern Venus does. 这些模型显示，两十亿年来，虽然金星比现在的地球要多吸收40%的太阳辐射，但它可能依然有温和的，类似地球的温度和液态海洋。当然这取决于以前的金星是否跟现在转的一样慢。 “If Venus was spinning more rapidly, all bets are off, ” Michael Way, lead author of a new study that has been submitted for publication in Geophysical Research Letters told Gizmodo. But, under the right conditions, “you get temperatures almost like Earth. That’s remarkable.” “如果金星转的速度很快，那么所有的一切就不成立，”已在《地球物理学研究快报》提交出版的一项新研究主要作者，Michael Way告诉Gizmodo。但是，在适当的条件下，“它的温度几乎接近地球。那就是了不起的发现。“ The habitability of Earth and Mars have changed throughout the lifetime of the solar system. Geologic evidence suggests that Mars was much wetter in the distant past, although whether the Red Planet had liquid water oceans or was frozen under a mantle of ice is still a matter of debate. Earth, meanwhile, has swung from hothouse to icehouse and back, all the while accumulating oxygen in its atmosphere and becoming a more favourable place for complex life. 在太阳系的演化过程中，地球和火星的居住环境已经发生了改变。地质证据表明，火星在遥远的过去更加潮湿，但这颗红色星球否有液态海洋还是地幔下冻结的冰块仍是一个有争议的问题。反观地球，从温室到冰窖反反复复，同时积累了大气中的氧气，并成为一个更有利复杂生命生存的地方。 But what about Venus? The past habitability of Earth’s nearest neighbour has received scant attention compared with that of Mars. Our bias may stem from the fact that modern day Venus is so forbidding, with its impenetrably thick atmosphere, toxic thunderclouds and atmospheric pressure nearly 100 times higher than that of Earth. When a planet turns spacecraft after spacecraft into a puddle of goo within seconds, it’s only natural for people to get frustrated and turn their attention elsewhere. 但相比较火星，金星作为过去和地球最接近的栖息地，几乎没有获得多少关注。我们的偏见可能来自，现代金星是那么可怕的，其严密的大气层，有毒雷云和比地球高出近100倍的大气压。当一个行星没过几秒就让人们发射出一个又一个的航天器陷入泥坑，人们感到沮丧和并把注意力转到其他地方也是自然不过。 Still, just because Venus is weird and awful today doesn’t mean it always was. The entire surface was reworked by volcanic activity some 700 million years ago, and we have no idea what Venus looked like before that. But measurements of the hydrogen isotope ratio in Venus’ atmosphere imply that the planet used to have much more water — maybe enough to support oceans. 不过，现在金星的怪异和可怕并不意味着它以前也一直也是这样。整个表面在7亿年前因火山活动而被重塑，所以我们没法知道金星之前长什么样。但通过测量金星大气中的氢同位素的比值，这个星球曾经可能有过更多的水 - 也许足以生成海洋。 Taking a first stab at the question of whether Venus was once habitable, Way and his colleagues combined a global topographic dataset collected by the Magellan spacecraft with water and solar radiation estimates for past Venus. All of this information was plugged into global climate models, similar to those used to study climate change on Earth today. 对于金星曾经是否适合居住这一问题，Way和他的同事做的第一件事就是，结合麦哲伦航天器收集的全球地形数据集和对过去金星水和太阳辐射的估算。所有这些信息被代入到全球气候模型，类似于今天研究地球上气候变化的方式。 The initial results were encouraging. Despite the fact that ancient Venus would have received much more sunlight than modern Earth 2.9 billion years ago, Way’s models predict an average surface temperature of just 11C. By 715 million years ago, the surface would have only warmed up four degrees — meaning Venus could have had a temperate climate for at least 2 billion years. 初步结果令人鼓舞。尽管古代金星在29亿年前比现在的地球获得更多的阳光，Way的模型预测其表面平均温度只有11摄氏度。 截至7.15亿年前，其表面温度也只上升四度 - 这意味着金星可能有至少20亿年的温带气候。
最近的研究表明，金星上强大的“电气风”可以帮助水汽脱离这颗行星的大气层。图片：NASA There is, however, a catch: Those numbers are entirely dependent on past Venus having similar topography and orbital characteristics to modern Venus. When Way re-ran his models but gave 2.9 billion year-old Venus a facelift to look like modern day Earth, surface temperatures rose considerably. 然而，有一个难题：这些数字是完全依赖于过去金星与现在金星具有类似的地形和轨道特性。当Way针对类似地球的地形给29亿岁的金星重跑了他的模型，其表面温度有明显的上升。 “We wanted to see what effect topography might have had on the climate state of this world,” Way said. “Sure enough, it had a big effect.” The reason, he says, probably has to do with changes in the amount of reflective surface on Venus, and shifting atmospheric dynamics. “我们想看看地形对这个世界的气候会产生什么样的影响，”Way说。 “果然，它带来很大的影响。”究其原因，他说，可能是由于金星表面的改变影响了阳光的反射，从而使得大气层动态变化着。 Another fascinating twist has to do with Venus’ rotation. In his initial models of 2.9 billion year old Venus, Way stuck with a slow, modern-day rotational period of 243 Earth days. But when he spun Venus up to give it a 16 Earth-day period, the planet once again became a pressure cooker. 另一个奇妙的怪异点在于金星的公转。在他对29亿岁金星的最初的模型中，Way使用一个现在的缓慢公传周期，相当于243个地球日。但是，当他把金星的公转周期加速到16个地球日时，这颗行星再次成为一个高压锅。 This has to do with the impact of Venus’ rotational rate on atmospheric circulation patterns called Hadley cells. 金星的这种旋转速率对大气环流的影响称为哈德利环流。 “Earth has many [circulation] cells because our planet rotates fast,” Way said. “But if you rotate slowly, you have one in the north and one in the south, period. That changes the atmospheric dynamics of the world by a significant amount.” “地球上有很多种环流，是因为我们的地球旋转快，”Way说。 “但如果你慢慢地旋转，你只有一个北极环流和一个南极环流。这些都会对显著改变世界上的大气动力学“。 Specifically, slow-rotating Venus develops a gigantic cloud right at the sub-solar point, that is, where the sun’s rays are hitting the surface dead on. This basically turns the atmosphere of Venus into a giant solar reflector. When Venus rotates more quickly, this pattern doesn’t form. 具体地，缓慢旋转的金星会在日下点产生一片巨大的云，因此，所有照在这表面的太阳光线都无法到达行星内部。这基本上使得金星的大气层成为了一个巨大的太阳能反射器。当金星更快速地旋转，这种情况将不会形成。 While the study doesn’t actually confirm that Venus was once habitable, it does point to a plausible scenario in which Venus could have been. It’s worth noting that a planet’s rotation rate can change dramatically over time — Earth’s rotation is gradually slowing down because of the Moon — and some researchers suspect that Venus spun more quickly in the past. But there’s no easy way for us to find out. We could get indirect evidence by doing population studies on small, rocky exoplanets in Venus-like orbits. 虽然这项研究并没有真正证实金星曾经是可居住的，但它指向了一个可信的情景，这个情景可能就是金星曾经经历的。值得注意的是一颗行星的旋转速度可随时间发生显著变化 - 地球因为月球的存在旋转速度才逐渐减慢 - 一些研究人员怀疑，金星过去更迅速地旋转。但对我们来说没有简单的方法。我们只能通过研究星族轨道来获得间接证据，如系外类似金星的小型岩质行星。 And, if Venus was a balmy paradise for billions of years, one has to wonder what sort of apocalypse led to the present-day situation. 而且，如果金星在数十亿年间都是一个温和天堂，人们想知道什么样的灾变导致了现今的局面。 “We really need more data before we can say much more,” Way said. But, he added, the study does indicate that worlds in Venus-like orbits should not immediately be deemed uninhabitable. “我们确实需要更多的数据才能揭示的更多，”Way说。但是，他补充说，这项研究确实表明，当发现类似金星轨道的行星，不应该立即认为其不适合居住。 “In plots of the habitable zone, you typically see Venus on the outside,” he said. “And for modern day Venus, that’s certainly true. But, if you have a Venus-like world around a solar-type star with a slow rotation, it could be quite a reasonable place for life to exist, especially in the oceans.” “在对可居住对象的研究中，你通常会看到金星被排除在外，”他说。 “而对于现在的金星，这么做毫无疑问。但是，如果你发现了一个类似太阳系中的缓慢旋转的金星，这可能是生命存在的地方，尤其是在海洋中。“ A past-habitable Venus also opens up new possibilities about the origin of life on Earth. From meteorites, we know that Earth and Mars were swapping material in the distant past, prompting astrobiologists to wonder whether the Red Planet could have seeded our world with life. But if life was just as likely to emerge on Venus, that’s one more planet to add to mix. Incredibly, we don’t know whether there are any meteorites from Venus here on Earth, because we’ve never been able to analyse a rock on Venus for comparison. 一个过去可居住的金星同时也暗示着地球生命起源的新的可能性。从陨石中，我们知道，地球和火星都在遥远的过去交换物质，促使太空生物学家怀疑这颗红色星球是否可能将生命播种到我们生活的世界。但是，如果金星中可能出现生命，那么将有多一个星球混合进来。令人难以置信的是，我们不知道是否有来自金星的陨石落在地球上，因为我们从来没有去分析金星上的岩石从而进行比较。 Until then, we can’t deny the possibility that our distant ancestors were actually born on that torrid acid bath next door. “It could be that life got started on Venus, and then seeded Earth,” Way said. “Or vice-versa.” 在此之前，我们不能否认，我们的远祖可能实际上出生在隔壁那个炎热的酸浴行星上。 “可能生命开始于金星，然后播种地球,”Way说。 “或者相反。”(翻译：杨乃漳) |
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