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Science and Technolgy
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Another Earth?
另一個地球？
Home away from home
遠離家鄉的家
The existence of the most Earthlike planet yet has just been confirmed
類地球行星的存在已剛被確認
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.
在過去幾天的Durban氣候變化會談上提出的較難忘的口號之一就是"沒有星球B"，但是如果有呢？在過去的幾十年內，天文學家記載了數以千計的所謂的"外行星"---饒太陽以外的星球軌道運行的宇宙。12月5號，負責開普勒號的科學家確認他們的儀器發現了第一個類地球星體，開普勒號是專門為尋找這樣的類地球星體而設計的太空望遠鏡。
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.
存在這么一個行星，它環繞天琴座星系中一顆600光年遠的恒星運行，之前被懷疑的不存在，開普勒號，隸屬于美國國家航空與宇宙航行局，即美國航天局，它通過觀察當行星通過時恒星光亮度的變化來工作。它標識顯現的光度弱化可能為候選行星，開普勒22b就是一個。但是一個行星的確認需要通過三個檢測，開普勒22b現在已經通過檢驗。最重要的是，他環繞著其恒星的"適居帶"很好地運行；不會太近也不太遠（因此，可能，生命）液體水可能存在在上面。
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.
它加入了另外兩個類地球行星——Gliese 581d 和HD 85512 b—在過去的幾年里被另外的儀器發現的。事實上，"類地球行星"這個詞言過其實，Kepler 22b半徑是地球的2.4倍，如果它和地球的組成大致相同，它的表面引力也將大約高達地球引力的2.4倍。但是美國國家航天與宇宙航行局的天文學家仍不能確定它主要是氣體的、液體的或是固體的。
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 是目前發現的最有希望的外行星。不像其他行星不在恒星的"適居帶"，Kepler 22b 在它的"適居帶"舒適地運行。美國國家航空與宇宙航行局的研究人員通過與地球表面溫度15°C（至少現在是）比較，估算出它表面的溫度大概是22°C。它的母恒星與太陽相似，這又與其他兩個候選外行星不同，其他兩個候選外行星都環繞較冷的、較昏暗的恒星運行。Gliese 581d的母恒星確實是一個紅矮星---最小的星系。那意味著'適居帶"非常接近它以至于行星可能被潮汐力鎖住，就像月亮對于地球一樣。如果是那樣的話，Gliese 581d的一面將會是常年光亮的（并很熱），而另一面將會是無盡的黑暗。
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這三個可能適合居住的外行星中。Kepler自發射以來的2年半里已經發現了2,326候選行星。其他儀器大約發現了另外650個行星。大量的行星使天文學家開始得出行星種類繁多的結論。Kepler捕獲的行星中9%大小與地球相似(盡管不是所有的都在他們恒星的"適居帶")；Kepler 發現的行星29%是超級地球---實質上比地球大，不過地球是巖石類行星。Kepler未能確認的候選行星48%看起來似乎是在"適居帶"運行；其中，有10個與地球大小類似。
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.
當然最終的目標是讓天文學家對銀河系的行星總數、確定可以維持生命的行星數和那些可以維持人類殖民者生命（至少在理論上）的行星比例做出一個接近可信的估算。如果Kepler類地行星中只有很少被證明是真的，第三個數可能是數百萬。
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
一位牛津大學的天文學家Chris Lintoot說這些知識是歷史轉變的標志，他對Kepler團隊給以數據分析的援助，從此關于其他地方是否存在生命問題的不確定性將不再是天文學問題（有多少合適的行星），而是變成了純粹的生物問題（生命開始難不難？進化到聰明難不難？）基于這些初始數據，似乎有許多合適的行星，外空生物學將不再是一個矛盾修飾。
