When a world is born(幼星降生之谜)
关键词： born，幼星，降生Planetary science
行星科学
The discovery of new planets has forced a rethink of how they formed
新行星的发现让我们不禁反思：它们是怎样形成的呢？
A WHIRLING, swirling, circumstellar cloud of dust and gas gave birth to the Earth, or so astrophysicists have long believed. But recent discoveries of planets outside the solar system—exoplanets）, to give them their proper name—have made scientists suspect that not all such objects can have formed in the same way as the Earth and her neighbours. This insight raises the possibility that the universe contains many more exoplanets than was previously thought.
一团尘埃和气体绕着太阳不断旋转并形成旋涡，接着地球诞生了——至少天体物理学家们长期以来都是这样认为的。但是，最近不断有太阳系以外的行星——它们被形象地称为太阳系外行星（以下均简称系外行星）——被发现，这让科学家们开始怀疑：并非所有这类天体的形成方式与地球及地球的邻居们相同。这种观点提出了这样一种可能性，即宇宙中实际的系外行星数量比之前预想的要大得多。
The first such new world was discovered in 1993 by researchers at Pennsylvania State University. It was thought to be unusual in that the star it orbits is a pulsar—a rapidly rotating, extraordinarily dense neutron star that emits no light. Two years later Michel Mayor and Didier Queloz, of the Geneva Observatory, in Switzerland, spotted a gaseous giant—the same sort of planet as Jupiter, Uranus and Neptune—circling a sun-like star called 51 Pegasi. This exoplanet looked unusual too, because it orbits its host star at a mere twentieth of the distance of the Earth from the sun.
1993年，宾夕法尼亚州立大学的研究人员首次发现了一颗系外行星。因为它围绕旋转着的是一颗脉冲星[2]——一类快速旋转、密度异乎寻常之大且不发光的中子星，这一发现在当时被认为非常奇特。两年以后，瑞士日内瓦天文台的米歇尔·麦耶（Michel Mayor）和迪迪尔·奎洛兹（Didier Queloz）观测到了一颗气态巨星（gaseous giant）——同木星、天王星和海王星等同类型的行星——围绕一颗类太阳恒星（sun-like star）运转，那颗恒星被称为飞马座51 [3]。从外观上看，这颗系外行星也不同寻常，因为它的运行轨道同主星（host star）的距离仅为日地距离[4]的二十分之一。
Astronomers have since detected more than 200 exoplanets, and such quirks are no longer novel: in their positioning or in some other respect, most differ substantially from the planets of the solar system. And astronomers hope to see in the differences they observe among exoplanets evidence of differences in the ways these bodies were created.
此后，天文学家们先后又发现了200多颗系外行星，而且在这些行星中，上述奇观也不再新鲜：就轨道的位置或其他方面来看，大多数行星同太阳系的行星存在根本的差异。况且，通过观察这些系外行星的差异，发现这些行星成因不同的证据，正是天文学家们所期待的。
Astrophysicists generally agree that planets, whether they are small and rocky, like the Earth, or gaseous giants, like most of the exoplanets discovered so far, form from the disc of dust and gas that surrounds a nascent star. Researchers had seen debris discs around exoplanets' host stars, but until recently they had not seen whether the discs and the planets' orbits were aligned. They have now. Astronomers led by Fritz Benedict and Barbara McArthur, of the University of Texas, Austin, examined the Earth's nearest known exoplanet neighbour—a gaseous giant orbiting the sun-like star Epsilon Eridani, 10.5 light years away in the constellation Eridanus. They found that its orbit is inclined at 30 degrees to the Earth's, the same angle at which the star's disc of dust and gas is tilted. The results will appear in the November issue of the Astronomical Journal. So far, so good.
天体物理学家们普遍认同：迄今为止所发现的行星，无论是如同地球般小巧、岩性亦或类似大多数系外行星般巨大、气态，都是漂浮在新生恒星周围、由尘埃和气体组成的“盘”构成的。研究人员已经在系外行星的主星周围观察到了碎屑盘（debris discs）[5]，但是直到最近以前，他们并不确定这些碎屑盘同行星是否处在同一轨道上。现在这一问题已经得到了确认。在弗里兹·本尼迪特（Fritz Benedict）和芭芭拉·麦克阿瑟（Barbara McArthur）带领下，得克萨斯大学（奥斯汀）的天文学家们探测了一颗系外行星，这是已知的系外行星中离地球最近的一颗。这是一颗气态巨星，其运行轨道围绕的是一颗类太阳恒星——天苑四[6]，距离猎户座（constellation Eridanus）10.5光年。他们发现这颗行星轨道同地球的倾角是30度，而恒星的碎屑盘相对地球倾斜的角度同样是30度。研究结果将刊登在11月份的《美国天文学杂志》（the Astronomical Journal）上。到目前为止，一切都如预想的那样。
Dust to dust
尘里来，尘里去
Exactly how gaseous giants emerge from discs of debris, though, is a matter of debate. The accepted wisdom has been that the planets grow from a core of solid material that, once it reaches a critical mass, has enough gravitational pull to attract most of the gas in its orbit. This must happen some distance from the parent star, where conditions are cool enough for sufficient material to be in a solid rather than gaseous form. The so-called ice line, beyond which this happens, is typically three times the distance from the sun to the Earth for sun-like stars.
但是，针对气态巨星怎样从碎屑盘中形成这个问题，大家争论不休。大家一致公认的是：一旦固态物质的质量达到某个临界值、具有足够的引力吸引轨道上的大部分气体，行星便会以此为核心逐渐形成。但这一过程必须发生在距离母星（parent star）的某个位置，那里的温度较低，有足够多的物质以固态而非气态形式存在。对于类似太阳的恒星来说，所谓的冰线（ice line）——大于这个距离，上述的温度条件才能得到满足——往往三倍于日地距离。
Most of the exoplanets discovered so far are much closer to their host stars than the ice line. These observations are lending strength to an alternative hypothesis: that the gaseous giants detected so far formed elsewhere and have since spiralled towards the stars they now orbit. This could happen if the material in a protoplanetary discgradually saps the exoplanet's angular momentum, or if the disc's dust and gas swirls into the star, dragging the exoplanet along with it.
至今所发现的系外行星中，大多行星同主星的距离小于冰线。这些发现有力地支持了另一种假设：迄今所发现的气态巨星是在其他地方形成的，并且朝现行轨道绕行的恒星螺旋状前进。如果原行星盘（protoplanetary disc）[7]内的物质会逐渐消耗掉这些行星的角动量，或者，盘内的尘埃和气体朝主星作螺旋状运动进而带动整个行星，那么这种情况就可能发生。
But this is not the only alternative explanation. Another version has it that large and small protoplanetary discs of the same mass may form exoplanets differently. Large discs—like that from which the solar system is thought to have formed—might create gaseous giants farther away from the host star while smaller discs might allow such objects to form closer in.
但这并不是备选假设的唯一版本。另一种说法认为大小不一但质量相同的原行星盘就可能形成各自不同的系外行星。较大的盘——类似于认为形成太阳系的原行星盘——可能会产生距离主星稍远的气态巨星，而较小的盘可能会形成距离主星更近的天体。
Unfortunately, the evidence collected so far does not allow astronomers to say which of these ideas, if any, is correct. Earlier this month, for example, the Hubble Space Telescope spotted 16 possible exoplanets closely circling far-flung stars near the centre of the Milky Way. (This is exciting, because it implies that exoplanets are quite common and that there may be as many as 6 billion gaseous giants in the galaxy.) Yet because the host stars are relatively dim, they may not have been hot enough to boil away the building blocks of exoplanets. Or the exoplanets could have migrated there.
不幸的是，现有的证据并不足以令天文学家们判断这些假设中孰是孰非（如果其中确有正确的话）。例如，本月早些时候，哈勃太空望远镜搜索到了16颗紧密围绕银河中心附近的恒星带旋转的系外行星（这一发现令人振奋，因为它意味着系外行星相当普遍，而且银河系中的气态巨星可能有60亿颗之多。）。但是，因为这些主星的亮度相对偏淡，所以它们可能没有足够的高温令系外行星的主体结构气化。否则，这些行星就可能是外来的。
Stranger sightings have also been made, which may rewrite theories of planetary formation completely. A month ago astronomers at the Harvard-Smithsonian Centre for Astrophysics announced that they had found a truly exotic exoplanet. The object, dubbed HAT-P-1, is the biggest gaseous giant yet discovered. It orbits one of a pair of stars 450 light years away, in the constellation Lacerta, circling its host every few days. Its distance from this star is only 5% of that between the Earth and the sun. The body's density is extremely low—comparable to that of cork. Moreover, HAT-P-1 is the second exoplanet that is much bigger and less dense than theory predicts. Astrophysicists are baffled as to how such a world could form; a paper describing the discovery has been submitted to the Astrophysical Journal.
此外，人们还观察到了一些更为离奇的现象，这可能会彻底颠覆各种行星诞生理论。一个月前，哈佛－史密森天体物理中心（Harvard-Smithsonian Centre for Astrophysics）的天文学家宣称他们发现一颗异乎寻常的系外行星。这个编号为HAT-P-1的天体是迄今发现的最大气态巨星。该行星围绕蝎虎座（constellation Lacerta）一对恒星（双星系统）中的其中一颗运行，距离地球450光年。这颗行星每隔几天就能绕主星公转一周，且与主星之间的距离仅为日地距离的5%。它的密度小得出奇——同软木塞相当。此外，HAT-P-1是第二颗在体积上大于而在密度上小于理论预测值的行星。对于这颗行星的成因，天体物理学家们都迷惑不解，；一篇描述此项发现的论文已经投到了《天体物理学杂志》（Astrophysical Journal）。
This follows the discovery last year by Maciej Konacki, of the California Institute of Technology, of a gaseous giant orbiting a star that is itself orbited by a binary-star system. Such an arrangement would have quickly shed its protoplanetary discs, so how exactly the exoplanet came to be formed is a mystery.
这次发现是先前一项发现的继续。去年，加州理工大学的Maciej Konacki发现了一颗围绕双星系统中的一颗恒星旋转的气态巨星[8]。双星系统本应在短时间内清除原行星盘，因此，这颗行星的确切成因还是一个谜。
The discovery of exoplanets in binary and triple-star systems raises the prospect that the galaxy houses many more such objects than was previously thought. More than 60% of the stars in the Milky Way have a companion star around which they orbit. Most searches for exoplanets have avoided such systems, because the presence of two stars complicates matters. But given that exoplanets could well form in many different ways, astrophysicists believe that taking a closer look at the neglected majority of double stars may reveal a galaxy full of new worlds.
从双星和三星系统中存在行星的发现中产生了这样一种观点，即银河系中包容的天体远比先前所认为的要多。银河中超过六成的恒星在其运行轨道附近存在伴星。由于引入双星系统会增加问题的复杂性，大多数搜索系外行星的研究都将这类系统排除在外。但是，考虑到通过许多不同的方式能够形成完整的系外行星，天体物理学家们相信将目光移近那些过去一直被忽略的大量双星系统中，可能会在银河系中发现新行星到处都是。
Finding out just how common exoplanets are—particularly the rocky, Earth-like sort—will be the task of two space-based telescopes to be launched within the next couple of years. All being well, a French spacecraft called COROT, backed by the European Space Agency, will take off in December. It has been designed to spot exoplanets bigger than twice the size of the Earth. America's space agency, NASA, plans to launch a more ambitious exoplanet-hunter, called Kepler, in October 2008. It should be capable of detecting exoplanets smaller than the Earth.
就探索系外行星的普遍性而言——尤其是岩状类地天体——这是在几年内即将送入太空的两架空间望远镜的使命。若一切就绪，一艘由欧洲航天局（ESA）共同研制的称为COROT的法国太空飞船将在12月发射升空。这艘太空船是用以捕捉体积在地球两倍以上的系外行星的踪影。美国航天部门——国家航空航天局（NASA）计划在2008年10月将一架功能更为强劲、称为“开普勒”[9]的“系外行星捕捉者”送入太空。这架望远镜能够侦测到体积比地球还小的系外行星。
The observatories will monitor regions of the galaxy continuously, in order to detect exoplanets as they pass between their host star and the Earth. The astronomers who will use these telescopes are particularly interested in finding any Earth-like objects in the so-called habitable zone around a star, where temperatures permit water to exist in a liquid state. They hope to detect hundreds of such exoplanets and, in so doing, learn more about how new worlds and even life itself might emerge from dust and debris.
各天文台也会不断地观测银河系的各个区域，目的就是当系外行星运行到主星和地球之间时发现它们[10]。利用这些空间望远镜观察的天文学家们尤其对恒星周围所谓“适居带（habitable zone）”里的类地天体感兴趣。在适居带内，适宜的温度刚好让水保持液态。他们希望能够找到数百颗这样的系外行星，借此，进一步了解尘埃和残骸究竟如何形成行星，甚至生命本身。
注释：
[1] 题目When a world is born改自一首著名的歌曲名：When a child is born（当圣婴降生时）
[2] 脉冲星是大质量恒星在演化末期而形成的中子星，它能发射出的有规律的周期性电磁辐射脉冲。
[3] 飞马座51（51 Pegasi）是位于飞马座的一颗类似太阳的恒星，距离太阳系约47.9光年。1995年被发现有行星围绕该恒星公转，是继太阳系外，首个被证实有行星的恒星。飞马座行星的发现引起多个争论，因为飞马座51与行星的近距离并不合乎已知的行星诞生理论，并引发了轨道改变的讨论。有说法指该行星可能处于毁灭的阶段。
[4] 日地距离是149,597,870千米
[5] 碎屑盘（debris discs）是指围绕在类太阳恒星附近的行星碎屑带，主要是由类似小行星岩性天体碰撞产生的尘埃扩散后形成
[6] 天苑四 (Epsilon Eridani)是很靠近猎户座腰帶的一颗恒星，和太阳很像的恒星，距离地球仅10光年
[7] 原行星盘（protoplanetary disc）是指围绕新生恒星的气体和尘埃组成的盘，盘中粒子间的碰撞最终产生行星。
[8] 这颗行星的编号为HD 209458b，它的体积较理论计算值大了将近20％
[9] “开普勒”是一个直径一米的望远镜。当行星从恒星表面掠过的时候，对于观察者，恒星的亮度会稍微降低。“开普勒”的工作就是辨别出这样的亮度降低现象，尤其是类似地球这样的行星造成的亮度降低。
[10] 这一原理被称为“多普勒摆动”：这种摆动意味着恒星附近有一个天体，其引力影响着恒星的运动。在很偶然的情况下，恒星－行星－地球三者成一直线，行星的引起的“日食”使恒星光芒在地面观察者看起来暂时减弱，由恒星亮度变化就可发现行星的存在。前文提到的飞马座51的行星也是通过多普勒侦测法侦测到的。翻译 by edenbahamut
行星科学
The discovery of new planets has forced a rethink of how they formed
新行星的发现让我们不禁反思：它们是怎样形成的呢？
A WHIRLING, swirling, circumstellar cloud of dust and gas gave birth to the Earth, or so astrophysicists have long believed. But recent discoveries of planets outside the solar system—exoplanets）, to give them their proper name—have made scientists suspect that not all such objects can have formed in the same way as the Earth and her neighbours. This insight raises the possibility that the universe contains many more exoplanets than was previously thought.
一团尘埃和气体绕着太阳不断旋转并形成旋涡，接着地球诞生了——至少天体物理学家们长期以来都是这样认为的。但是，最近不断有太阳系以外的行星——它们被形象地称为太阳系外行星（以下均简称系外行星）——被发现，这让科学家们开始怀疑：并非所有这类天体的形成方式与地球及地球的邻居们相同。这种观点提出了这样一种可能性，即宇宙中实际的系外行星数量比之前预想的要大得多。
The first such new world was discovered in 1993 by researchers at Pennsylvania State University. It was thought to be unusual in that the star it orbits is a pulsar—a rapidly rotating, extraordinarily dense neutron star that emits no light. Two years later Michel Mayor and Didier Queloz, of the Geneva Observatory, in Switzerland, spotted a gaseous giant—the same sort of planet as Jupiter, Uranus and Neptune—circling a sun-like star called 51 Pegasi. This exoplanet looked unusual too, because it orbits its host star at a mere twentieth of the distance of the Earth from the sun.
1993年，宾夕法尼亚州立大学的研究人员首次发现了一颗系外行星。因为它围绕旋转着的是一颗脉冲星[2]——一类快速旋转、密度异乎寻常之大且不发光的中子星，这一发现在当时被认为非常奇特。两年以后，瑞士日内瓦天文台的米歇尔·麦耶（Michel Mayor）和迪迪尔·奎洛兹（Didier Queloz）观测到了一颗气态巨星（gaseous giant）——同木星、天王星和海王星等同类型的行星——围绕一颗类太阳恒星（sun-like star）运转，那颗恒星被称为飞马座51 [3]。从外观上看，这颗系外行星也不同寻常，因为它的运行轨道同主星（host star）的距离仅为日地距离[4]的二十分之一。
Astronomers have since detected more than 200 exoplanets, and such quirks are no longer novel: in their positioning or in some other respect, most differ substantially from the planets of the solar system. And astronomers hope to see in the differences they observe among exoplanets evidence of differences in the ways these bodies were created.
此后，天文学家们先后又发现了200多颗系外行星，而且在这些行星中，上述奇观也不再新鲜：就轨道的位置或其他方面来看，大多数行星同太阳系的行星存在根本的差异。况且，通过观察这些系外行星的差异，发现这些行星成因不同的证据，正是天文学家们所期待的。
Astrophysicists generally agree that planets, whether they are small and rocky, like the Earth, or gaseous giants, like most of the exoplanets discovered so far, form from the disc of dust and gas that surrounds a nascent star. Researchers had seen debris discs around exoplanets' host stars, but until recently they had not seen whether the discs and the planets' orbits were aligned. They have now. Astronomers led by Fritz Benedict and Barbara McArthur, of the University of Texas, Austin, examined the Earth's nearest known exoplanet neighbour—a gaseous giant orbiting the sun-like star Epsilon Eridani, 10.5 light years away in the constellation Eridanus. They found that its orbit is inclined at 30 degrees to the Earth's, the same angle at which the star's disc of dust and gas is tilted. The results will appear in the November issue of the Astronomical Journal. So far, so good.
天体物理学家们普遍认同：迄今为止所发现的行星，无论是如同地球般小巧、岩性亦或类似大多数系外行星般巨大、气态，都是漂浮在新生恒星周围、由尘埃和气体组成的“盘”构成的。研究人员已经在系外行星的主星周围观察到了碎屑盘（debris discs）[5]，但是直到最近以前，他们并不确定这些碎屑盘同行星是否处在同一轨道上。现在这一问题已经得到了确认。在弗里兹·本尼迪特（Fritz Benedict）和芭芭拉·麦克阿瑟（Barbara McArthur）带领下，得克萨斯大学（奥斯汀）的天文学家们探测了一颗系外行星，这是已知的系外行星中离地球最近的一颗。这是一颗气态巨星，其运行轨道围绕的是一颗类太阳恒星——天苑四[6]，距离猎户座（constellation Eridanus）10.5光年。他们发现这颗行星轨道同地球的倾角是30度，而恒星的碎屑盘相对地球倾斜的角度同样是30度。研究结果将刊登在11月份的《美国天文学杂志》（the Astronomical Journal）上。到目前为止，一切都如预想的那样。
Dust to dust
尘里来，尘里去
Exactly how gaseous giants emerge from discs of debris, though, is a matter of debate. The accepted wisdom has been that the planets grow from a core of solid material that, once it reaches a critical mass, has enough gravitational pull to attract most of the gas in its orbit. This must happen some distance from the parent star, where conditions are cool enough for sufficient material to be in a solid rather than gaseous form. The so-called ice line, beyond which this happens, is typically three times the distance from the sun to the Earth for sun-like stars.
但是，针对气态巨星怎样从碎屑盘中形成这个问题，大家争论不休。大家一致公认的是：一旦固态物质的质量达到某个临界值、具有足够的引力吸引轨道上的大部分气体，行星便会以此为核心逐渐形成。但这一过程必须发生在距离母星（parent star）的某个位置，那里的温度较低，有足够多的物质以固态而非气态形式存在。对于类似太阳的恒星来说，所谓的冰线（ice line）——大于这个距离，上述的温度条件才能得到满足——往往三倍于日地距离。
Most of the exoplanets discovered so far are much closer to their host stars than the ice line. These observations are lending strength to an alternative hypothesis: that the gaseous giants detected so far formed elsewhere and have since spiralled towards the stars they now orbit. This could happen if the material in a protoplanetary discgradually saps the exoplanet's angular momentum, or if the disc's dust and gas swirls into the star, dragging the exoplanet along with it.
至今所发现的系外行星中，大多行星同主星的距离小于冰线。这些发现有力地支持了另一种假设：迄今所发现的气态巨星是在其他地方形成的，并且朝现行轨道绕行的恒星螺旋状前进。如果原行星盘（protoplanetary disc）[7]内的物质会逐渐消耗掉这些行星的角动量，或者，盘内的尘埃和气体朝主星作螺旋状运动进而带动整个行星，那么这种情况就可能发生。
But this is not the only alternative explanation. Another version has it that large and small protoplanetary discs of the same mass may form exoplanets differently. Large discs—like that from which the solar system is thought to have formed—might create gaseous giants farther away from the host star while smaller discs might allow such objects to form closer in.
但这并不是备选假设的唯一版本。另一种说法认为大小不一但质量相同的原行星盘就可能形成各自不同的系外行星。较大的盘——类似于认为形成太阳系的原行星盘——可能会产生距离主星稍远的气态巨星，而较小的盘可能会形成距离主星更近的天体。
Unfortunately, the evidence collected so far does not allow astronomers to say which of these ideas, if any, is correct. Earlier this month, for example, the Hubble Space Telescope spotted 16 possible exoplanets closely circling far-flung stars near the centre of the Milky Way. (This is exciting, because it implies that exoplanets are quite common and that there may be as many as 6 billion gaseous giants in the galaxy.) Yet because the host stars are relatively dim, they may not have been hot enough to boil away the building blocks of exoplanets. Or the exoplanets could have migrated there.
不幸的是，现有的证据并不足以令天文学家们判断这些假设中孰是孰非（如果其中确有正确的话）。例如，本月早些时候，哈勃太空望远镜搜索到了16颗紧密围绕银河中心附近的恒星带旋转的系外行星（这一发现令人振奋，因为它意味着系外行星相当普遍，而且银河系中的气态巨星可能有60亿颗之多。）。但是，因为这些主星的亮度相对偏淡，所以它们可能没有足够的高温令系外行星的主体结构气化。否则，这些行星就可能是外来的。
Stranger sightings have also been made, which may rewrite theories of planetary formation completely. A month ago astronomers at the Harvard-Smithsonian Centre for Astrophysics announced that they had found a truly exotic exoplanet. The object, dubbed HAT-P-1, is the biggest gaseous giant yet discovered. It orbits one of a pair of stars 450 light years away, in the constellation Lacerta, circling its host every few days. Its distance from this star is only 5% of that between the Earth and the sun. The body's density is extremely low—comparable to that of cork. Moreover, HAT-P-1 is the second exoplanet that is much bigger and less dense than theory predicts. Astrophysicists are baffled as to how such a world could form; a paper describing the discovery has been submitted to the Astrophysical Journal.
此外，人们还观察到了一些更为离奇的现象，这可能会彻底颠覆各种行星诞生理论。一个月前，哈佛－史密森天体物理中心（Harvard-Smithsonian Centre for Astrophysics）的天文学家宣称他们发现一颗异乎寻常的系外行星。这个编号为HAT-P-1的天体是迄今发现的最大气态巨星。该行星围绕蝎虎座（constellation Lacerta）一对恒星（双星系统）中的其中一颗运行，距离地球450光年。这颗行星每隔几天就能绕主星公转一周，且与主星之间的距离仅为日地距离的5%。它的密度小得出奇——同软木塞相当。此外，HAT-P-1是第二颗在体积上大于而在密度上小于理论预测值的行星。对于这颗行星的成因，天体物理学家们都迷惑不解，；一篇描述此项发现的论文已经投到了《天体物理学杂志》（Astrophysical Journal）。
This follows the discovery last year by Maciej Konacki, of the California Institute of Technology, of a gaseous giant orbiting a star that is itself orbited by a binary-star system. Such an arrangement would have quickly shed its protoplanetary discs, so how exactly the exoplanet came to be formed is a mystery.
这次发现是先前一项发现的继续。去年，加州理工大学的Maciej Konacki发现了一颗围绕双星系统中的一颗恒星旋转的气态巨星[8]。双星系统本应在短时间内清除原行星盘，因此，这颗行星的确切成因还是一个谜。
The discovery of exoplanets in binary and triple-star systems raises the prospect that the galaxy houses many more such objects than was previously thought. More than 60% of the stars in the Milky Way have a companion star around which they orbit. Most searches for exoplanets have avoided such systems, because the presence of two stars complicates matters. But given that exoplanets could well form in many different ways, astrophysicists believe that taking a closer look at the neglected majority of double stars may reveal a galaxy full of new worlds.
从双星和三星系统中存在行星的发现中产生了这样一种观点，即银河系中包容的天体远比先前所认为的要多。银河中超过六成的恒星在其运行轨道附近存在伴星。由于引入双星系统会增加问题的复杂性，大多数搜索系外行星的研究都将这类系统排除在外。但是，考虑到通过许多不同的方式能够形成完整的系外行星，天体物理学家们相信将目光移近那些过去一直被忽略的大量双星系统中，可能会在银河系中发现新行星到处都是。
Finding out just how common exoplanets are—particularly the rocky, Earth-like sort—will be the task of two space-based telescopes to be launched within the next couple of years. All being well, a French spacecraft called COROT, backed by the European Space Agency, will take off in December. It has been designed to spot exoplanets bigger than twice the size of the Earth. America's space agency, NASA, plans to launch a more ambitious exoplanet-hunter, called Kepler, in October 2008. It should be capable of detecting exoplanets smaller than the Earth.
就探索系外行星的普遍性而言——尤其是岩状类地天体——这是在几年内即将送入太空的两架空间望远镜的使命。若一切就绪，一艘由欧洲航天局（ESA）共同研制的称为COROT的法国太空飞船将在12月发射升空。这艘太空船是用以捕捉体积在地球两倍以上的系外行星的踪影。美国航天部门——国家航空航天局（NASA）计划在2008年10月将一架功能更为强劲、称为“开普勒”[9]的“系外行星捕捉者”送入太空。这架望远镜能够侦测到体积比地球还小的系外行星。
The observatories will monitor regions of the galaxy continuously, in order to detect exoplanets as they pass between their host star and the Earth. The astronomers who will use these telescopes are particularly interested in finding any Earth-like objects in the so-called habitable zone around a star, where temperatures permit water to exist in a liquid state. They hope to detect hundreds of such exoplanets and, in so doing, learn more about how new worlds and even life itself might emerge from dust and debris.
各天文台也会不断地观测银河系的各个区域，目的就是当系外行星运行到主星和地球之间时发现它们[10]。利用这些空间望远镜观察的天文学家们尤其对恒星周围所谓“适居带（habitable zone）”里的类地天体感兴趣。在适居带内，适宜的温度刚好让水保持液态。他们希望能够找到数百颗这样的系外行星，借此，进一步了解尘埃和残骸究竟如何形成行星，甚至生命本身。
注释：
[1] 题目When a world is born改自一首著名的歌曲名：When a child is born（当圣婴降生时）
[2] 脉冲星是大质量恒星在演化末期而形成的中子星，它能发射出的有规律的周期性电磁辐射脉冲。
[3] 飞马座51（51 Pegasi）是位于飞马座的一颗类似太阳的恒星，距离太阳系约47.9光年。1995年被发现有行星围绕该恒星公转，是继太阳系外，首个被证实有行星的恒星。飞马座行星的发现引起多个争论，因为飞马座51与行星的近距离并不合乎已知的行星诞生理论，并引发了轨道改变的讨论。有说法指该行星可能处于毁灭的阶段。
[4] 日地距离是149,597,870千米
[5] 碎屑盘（debris discs）是指围绕在类太阳恒星附近的行星碎屑带，主要是由类似小行星岩性天体碰撞产生的尘埃扩散后形成
[6] 天苑四 (Epsilon Eridani)是很靠近猎户座腰帶的一颗恒星，和太阳很像的恒星，距离地球仅10光年
[7] 原行星盘（protoplanetary disc）是指围绕新生恒星的气体和尘埃组成的盘，盘中粒子间的碰撞最终产生行星。
[8] 这颗行星的编号为HD 209458b，它的体积较理论计算值大了将近20％
[9] “开普勒”是一个直径一米的望远镜。当行星从恒星表面掠过的时候，对于观察者，恒星的亮度会稍微降低。“开普勒”的工作就是辨别出这样的亮度降低现象，尤其是类似地球这样的行星造成的亮度降低。
[10] 这一原理被称为“多普勒摆动”：这种摆动意味着恒星附近有一个天体，其引力影响着恒星的运动。在很偶然的情况下，恒星－行星－地球三者成一直线，行星的引起的“日食”使恒星光芒在地面观察者看起来暂时减弱，由恒星亮度变化就可发现行星的存在。前文提到的飞马座51的行星也是通过多普勒侦测法侦测到的。翻译 by edenbahamut
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