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For the first time, astronomers have discovered a world nearly the size of Earth orbiting a far star where water might exist as a life-giving liquid, the scientists announced Thursday.
科学家周四宣布，在围绕一颗遥远恒星运行的轨道上，天文学家首次发现了一颗大小与地球相近、并且可能存在水这种生命液体的行星。
Using the Kepler space telescope, Elisa Quintana of The SETI Institute at NASA's Ames Research Center in California and her colleagues detected the planet around a relatively cool red dwarf star in the constellation Cygnus, located about 459 light years from Earth.
通过使用开普勒(Kepler)太空望远镜，美国国家航空及太空总署(NASA)艾姆斯研究中心(Ames Research Center)地外文明搜寻研究所(The SETI Institute)的昆塔纳(Elisa Quintana)和同事发现了这颗行星。这颗行星环绕天鹅座(Cygnus)中一颗温度相对较低的红矮星运行，距离地球大约459光年。
Known officially as Kepler-186f, the planet is the outermost of five Earth-sized worlds orbiting in that star's solar system, the scientists said at a news conference held Thursday by the space agency. They also reported their findings in the journal Science.
科学家周四在NASA举办的新闻发布会上说，这颗行星的正式名称为开普勒-186f (Kepler-186f)，其所处的太阳系有五颗地球大小的行星，它是最外面的一颗。《科学》(Science)杂志刊登了这些科学家的发现。
In the search for worlds where life might take hold, scientists so far have detected 20 potentially habitable planets around other stars. But this one is the first so close in size to Earth that is located within its star's so-called habitable zone, where it receives the right amount of solar radiation so that water there wouldn't boil or freeze, the researchers said.
到目前为止，在搜寻可能存在生命的星球过程中，科学家已经发现了20个有孕育生命潜力的行星围绕其他恒星运转。但这次还是科学家们首次发现尺寸与地球如此接近，并位于所谓恒星“宜居带”的行星。研究人员们说，恒星“宜居带”是指行星所处位置能接收到不多不少的恒星辐射量，从而使行星上的水维持在液态。
'This is the first validated Earth-sized planet in the habitable zone of another star,' said Dr. Quintana. 'We can now say other potentially habitable worlds the size of Earth can exist.'
昆塔纳博士说，这是首次在另一个恒星“宜居带”确认发现地球大小的行星。她说，现在可以这样说，还有与地球大小类似、可能孕育生命的星球存在。
Other experts, though, cautioned that the planet orbits at the outer edge of that habitable zone, where it likely receives about the same amount of light as Mars in our own solar system. Kepler-186f could easily be so cold that any water there is frozen, unless it has a greenhouse-like atmosphere that can trap heat, they said.
不过，其他专家提醒说，这颗行星的运行轨道位于“宜居带”的外缘，那里接收到的光线可能与太阳系里的火星接收到的光线一样多。他们说，开普勒-186f很可能非常寒冷，水是冰冻状态的，除非那里有一个类似温室的环境，能够使热量滞留。
'It is Earth-sized, but not Earthlike,' said Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico, who wasn't involved in the research effort. 'The main point of this discovery is the size of the planet. So far, all potentially habitable planets were big ones.'
波多黎各大学(University of Puerto Rico)星球宜居性实验室主任门德斯(Abel Mendez)说，这颗行星的大小与地球类似，但环境与地球不同。门德斯没有参与这项研究。门德斯说，这项发现的主要一点是行星的大小，目前为止，全部可能宜居的行星体积都较大。
Given its small size, the researchers believe that Kepler-186f is most likely a rocky planet, but they don't have enough information to calculate its actual composition or mass. The researchers cannot see the planet directly, but detected it by measuring the periodic dip in light as it passes in front of its star.
鉴于开普勒-186f的体积较小，研究人员认为它最有可能是一颗岩态行星，但他们没有足够多的信息来计算出其实际成分或质量。研究人员无法直接看到这颗行星，而是通过测量它在其恒星前面经过时光线的周期性减弱而探测到它的。
Once the stuff of science fiction, such habitable planets may be common in the cosmos--as many as 40 billion Earthlike planets in the Milky Way, researchers estimate.
这类宜居行星过去都只是在科幻小说中才会出现。它们在宇宙中可能有很多，据研究人员估计，在银河系有多达400亿颗环境与地球类似的行星。
