经济学人下载:另一个地球? 远离家乡的家

Science and Technolgy
科技

Another Earth?
另一个地球？

Home away from home
远离家乡的家

The existence of the most Earthlike planet yet has just been confirmed
类地球行星的存在已刚被确认

ONE of the more memorable slogans to come out of the climate-change talks in Durban over the past few days is: "there is no planet B". But what if there were? Over the past couple of decades astronomers have logged thousands of so-called "exoplanets"—worlds which orbit stars other than the sun. On December 5th the scientists in charge of Kepler, a space telescope designed to look for such planets, confirmed their instrument's discovery of its first Earthlike world. It is dubbed, rather unromantically, Kepler 22b.
在过去几天的Durban气候变化会谈上提出的较难忘的口号之一就是"没有星球B"，但是如果有呢？在过去的几十年内，天文学家记载了数以千计的所谓的"外行星"---饶太阳以外的星球轨道运行的宇宙。12月5号，负责开普勒号的科学家确认他们的仪器发现了第一个类地球星体，开普勒号是专门为寻找这样的类地球星体而设计的太空望远镜。

The existence of this planet, which circles a star 600 light-years away, in the constellation of Lyra, had previously been suspected. Kepler, which belongs to NASA, America's space agency, works by observing dips in a star's brightness as a planet passes in front of it. It flags likely looking reductions as "candidate planets", of which Kepler 22b was one. But three passes are needed to confirm a planet's existence, and Kepler 22b has now passed this test. Crucially, it orbits well within its star's "Goldilocks zone": neither too close nor too far away for liquid water (and therefore, perhaps, life) to exist on its surface.
存在这么一个行星，它环绕天琴座星系中一颗600光年远的恒星运行，之前被怀疑的不存在，开普勒号，隶属于美国国家航空与宇宙航行局，即美国航天局，它通过观察当行星通过时恒星光亮度的变化来工作。它标识显现的光度弱化可能为候选行星，开普勒22b就是一个。但是一个行星的确认需要通过三个检测，开普勒22b现在已经通过检验。最重要的是，他环绕着其恒星的"适居带"很好地运行；不会太近也不太远（因此，可能，生命）液体水可能存在在上面。

It joins two other Earthlike planets-Gliese 581d and HD 85512 b-discovered by another instrument within the past few years. In truth, the term "Earthlike" is a stretch. Kepler 22b has a radius 2.4 times that of Earth, and if it is made from roughly the same stuff its surface gravity will also be about 2.4 times as strong. But NASA's astronomers remain unsure whether it is predominantly gaseous, liquid or solid.
它加入了另外两个类地球行星——Gliese 581d 和HD 85512 b—在过去的几年里被另外的仪器发现的。事实上，"类地球行星"这个词言过其实，Kepler 22b半径是地球的2.4倍，如果它和地球的组成大致相同，它的表面引力也将大约高达地球引力的2.4倍。但是美国国家航天与宇宙航行局的天文学家仍不能确定它主要是气体的、液体的或是固体的。

Nevertheless, Kepler 22b is the most promising exoplanet yet found. Unlike the others, which skirt the edges of their stars' Goldilocks zones, Kepler 22b orbits comfortably within its own. NASA's researchers reckon its surface temperature is about 22°C, compared with 15°C (at least for now) on Earth. Its parent star is similar to the sun, again unlike those of the other two candidates, both of which orbit cooler, dimmer stars. Indeed Gliese 581d's parent is a red dwarf-the tiniest stellar species. That means its Goldilocks zone is so close to it that the planet may be tidally locked, as the moon is to the Earth. If that were the case, one side of Gliese 581d would be permanently lit (and heated) while the other experienced unending darkness.
然而，Kepler 22b 是目前发现的最有希望的外行星。不像其他行星不在恒星的"适居带"，Kepler 22b 在它的"适居带"舒适地运行。美国国家航空与宇宙航行局的研究人员通过与地球表面温度15°C（至少现在是）比较，估算出它表面的温度大概是22°C。它的母恒星与太阳相似，这又与其他两个候选外行星不同，其他两个候选外行星都环绕较冷的、较昏暗的恒星运行。Gliese 581d的母恒星确实是一个红矮星---最小的星系。那意味着'适居带"非常接近它以至于行星可能被潮汐力锁住，就像月亮对于地球一样。如果是那样的话，Gliese 581d的一面将会是常年光亮的（并很热），而另一面将会是无尽的黑暗。

These three potentially habitable exoplanets may soon be joined by many more. In the two and a half years since its launch, Kepler has spotted 2,326 candidate planets. About 650 others have been discovered by other instruments. That plethora allows astronomers to start drawing conclusions about how common various sorts of planets are. Of Kepler's haul, 9% seem to be of a similar size to Earth (though not all are in the Goldilocks zone of their star); a further 29% are Super Earths-planets substantially larger than Earth that are nevertheless rocky. Forty-eight of Kepler's unconfirmed candidates look as if they orbit within their stars' habitable zones; of those, ten seem to be Earth-sized.
很快可能有更多的外行星加入这三个可能适合居住的外行星中。Kepler自发射以来的2年半里已经发现了2,326候选行星。其他仪器大约发现了另外650个行星。大量的行星使天文学家开始得出行星种类繁多的结论。Kepler捕获的行星中9%大小与地球相似(尽管不是所有的都在他们恒星的"适居带")；Kepler 发现的行星29%是超级地球---实质上比地球大，不过地球是岩石类行星。Kepler未能确认的候选行星48%看起来似乎是在"适居带"运行；其中，有10个与地球大小类似。

The ultimate goal, of course, is to let astronomers make a plausible estimate of the total number of planets in the galaxy, of the number that could conceivably support life, and of the fraction of those that could (at least in theory) sustain human colonists. If only a few of Kepler's possible Earthlike planets turn out to be real, that third number is likely to be in the millions.
 

当然最终的目标是让天文学家对银河系的行星总数、确定可以维持生命的行星数和那些可以维持人类殖民者生命（至少在理论上）的行星比例做出一个接近可信的估算。如果Kepler类地行星中只有很少被证明是真的，第三个数可能是数百万。

Such knowledge will mark an historic transition, says Chris Lintott, an astronomer at Oxford University who is giving the Kepler team a hand with the data analysis, since the uncertainties around the question of whether life exists elsewhere will cease to be astronomical (how many suitable planets are there?) and become purely biological (how easy is it for life to get going, and how easy is it for it to become intelligent?). Based on the preliminary data, it looks as if there are numerous suitable planets. The science of exobiology may soon cease to be an oxymoron
一位牛津大学的天文学家Chris Lintoot说这些知识是历史转变的标志，他对Kepler团队给以数据分析的援助，从此关于其他地方是否存在生命问题的不确定性将不再是天文学问题（有多少合适的行星），而是变成了纯粹的生物问题（生命开始难不难？进化到聪明难不难？）基于这些初始数据，似乎有许多合适的行星，外空生物学将不再是一个矛盾修饰。