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MOFFET FIELD, CALIFORNIA—NASA's Kepler space telescope appears to have confirmed the existence of an alien world smaller than our own Earth—the first time such a planet has been discovered around a star like our sun. However, scientists are reluctant to provide any details about the find—announced on Tuesday at the First Kepler Science Conference here at NASA's Ames Research Center—before their work is published, probably early next year. |
加州莫非特场消息——美国国家航空航天管理局（NASA）的开普勒太空望远镜证实了一颗系外星球的存在，该星球比我们的地球还要小，这是首次发现类地行星围绕着类日恒星旋转的情况。星期四，在莫非特场NASA埃姆斯研究中心举行的 “首届开普勒科学大会”上，宣布了这一发现。然而，科学家们的研究成果很可能将要在明年年初发表，在这之前他们不愿意透露该发现的详细情况。 |
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Despite its size, the new world—provisionally dubbed KOI-70.04—is very unlike our home planet. It orbits its star, a sun similar to our own known as Kepler-20, at a distance of just 9.6 million kilometers, completing one circuit every 6.1 days. Surface temperatures probably soar to almost 600°C, so there's no hope of finding liquid water there, let alone life. |
尽管这颗被临时称为“KOI-70.04”的新行星比较小，但是它跟作为我们家园的地球相比仍有很多不同之处。这颗行星在960万公里的近距离上围绕着其主恒星旋转，环绕一周仅用6.1天。这颗主恒星被称为“开普勒-20”，类似于我们的太阳。KOI-70.04的表面温度很可能高达近600°C，因而在那里是没有希望找到液态水的，更不用说寻找生命了。 |
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Just like Earth, KOI-70.04 is part of a multiplanet system. Four other, larger planets orbit the same star—one even closer in, and three farther away. All five planets are closer to their star than Mercury is to the sun. In that respect, the planetary system resembles Kepler-11, an extremely compact system of six planets announced in February. |
恰恰跟地球一样，KOI-70.04也位于一个多行星系统中：其他四颗较大的行星也环绕着同一颗恒星，其中一颗在距离恒星更近的内围，另外三颗距离恒星更远，但是所有的五颗行星距离它们的恒星都比水星距离太阳还要近。从这一点来看，这个行星系统很像2月份宣布的一个星球极为密集的系统——开普勒-11（包含着六颗行星）。 |
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The Kepler telescope, launched in March 2009, scrutinizes over 150,000 stars for tiny periodic dips in brightness that might mean orbiting planets are passing in front of the stars, blocking part of their light from reaching the telescope. But other observations need to confirm the true planetary nature of these candidate events, because the observed dips may also be due to an eclipsing binary star in the background whose light blends with the foreground star studied by Kepler. An eclipse within the background binary would mimic a small brightness dip in Kepler-20. |
开普勒望远镜于2009年3月份发射升空，它仔细审查了15万颗恒星，寻找在亮度上微弱的周期性变暗情况。这种变暗可能意味着轨道上的行星正在恒星前面经过，阻碍了恒星的部分光线到达望远镜。但是，还需要利用其他的观察来验证这些候选行星事件中真正的行星特性，因为所观察到的变暗也可能是这样形成的：在双星系统中，背景中一颗子星的光线跟前景中另一颗子星的光线混合，致使背景子星受到遮挡而变暗，被开普勒望远镜观察到。背景子星遭受遮挡变暗跟开普勒-20中的微弱变暗极为相似。 |
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The best way to confirm a candidate planet is by measuring the small, periodic wobbles it induces in its parent star. If that doesn't work, astronomers have a couple of other tricks up their sleeves to validate the planet. |
验证候选行星的最佳方法是，测量主恒星中微弱的周期性摆动，这种摆动是由行星引起的。如果该方法仍不奏效，天文学家们还可以利用其他几个验证行星的保留方法。 |
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Kepler project scientist Nick Gautier of NASA's Jet Propulsion Laboratory presented new data at the meeting on three of the larger planets in the Kepler-20 system, now officially known as Kepler-20b, -20c and -20d. From the star's wobbles, observed with ground-based telescopes, Gautier and his colleagues were able to deduce the masses of Kepler-20b and -20c: 8.7 and 16.1 Earth masses, respectively. Kepler-20d, the outermost planet in the system, was found to weigh in at less than 20.1 Earth masses. The three planets are between 1.9 and 3 times the size of Earth. |
开普勒望远镜项目的科学家、NASA喷气推进实验室的尼克·戈蒂埃在会议上提交了开普勒-20系统中三个较大行星的新数据，这三颗行星现在正式被称为开普勒-20b、开普勒-20c和开普勒-20d。通过地面望远镜观察到的恒星摆动，戈蒂埃及同事推测出开普勒-20b和开普勒-20c的质量分别为地球质量的8.7倍和16.1倍。开普勒-20d是该系统中最外围的行星，质量不超过地球质量的20.1倍。三颗行星的大小均介于地球的1.9倍至3倍之间。 |
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So what about the other two? "I can't disclose any details yet," says Fran?ois Fressin of the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who has a paper about the two smaller planets in press with Nature, "but if they are also validated, and if their size estimates are right, KOI-70.04 is significantly smaller than the Earth." KOI-70.04 was already in Kepler's list of candidate planets back in February, together with the three Kepler-20 planets described by Gautier; KOI-70.05 was found in June. |
那么，另外两颗行星的情况又是如何呢？“我还不能透露任何详细情况，”马萨诸塞州剑桥市哈佛-史密森天体物理中心的弗朗素瓦·弗雷桑说，“但是，如果这两颗行星也得到确认，如果对它们大小的估计也是准确的，行星KOI-70.04应该比地球小得多。”弗雷桑拥有一篇关于两颗较小行星的论文，准备发表在《自然》杂志上。早在2月份的时候，KOI-70.04和戈蒂埃描述的三颗开普勒-20行星就已经登上开普勒候选行星的列单了；行星KOI-70.05是六月份被发现的。 |
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Fressin won't confirm whether the two planets have indeed been validated, but if they weren't, they probably wouldn't warrant a Nature publication. Moreover, according to theoretical astrophysicist Jack Lissauer of NASA's Ames Research Center, "most Kepler multicandidates must be real planets." The reason is simple statistics: It's extremely unlikely to encounter two background eclipsing binaries (or one background binary and one genuine planet) at the same location. |
弗雷桑还不能肯定两颗小型行星是否真正地得到确认，如果没有得到确认，他们就不能保证论文能够在《自然》杂志上发表。此外， NASA埃姆斯研究中心的理论天体物理学家杰克·利索尔说：“开普勒望远镜发现的绝大多数系统中的多个候选行星一定是真正的行星。”原因在于一项简单的统计数据：在同一个位置，极不可能遇到两颗被遮挡的背景子星；或者，一颗为背景子星而另一颗为真正行星的情况也是不可能的。 |
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Indeed, asked about Kepler-20, Daniel Fabrycky of the University of California, Santa Cruz, confirmed that it is the first genuine five-planet system found by the space telescope. But while Fressin agrees that Lissauer's statistical argument is strong, he says validation of a candidate planet, especially one as small as KOI-70.04 appears to be, is of paramount importance. "I can't tell you anything more at this moment," he says. |
的确，当有人问及有关开普勒-20系列行星的情况时，加州大学圣克鲁兹分校的丹尼尔·法布里基肯定地说，这是开普勒太空望远镜所发现的首个真正的五行星系统。然而，尽管弗雷桑承认利索尔的统计证据是强有力的，但他表示一颗候选行星的确认，尤其是确认一颗看起来像KOI-70.04这么小的行星，是至关重要的。“目前，我不能透露其他情况了，”他说。 |
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From the data published in February and the new estimates for the properties of the parent star presented by Gautier, it would follow that KOI-70.04 is between 80% and 90% of the size of Earth. For KOI-70.05, no data have been released yet, except its orbital period, which, according to Gautier, is 19.6 days. In Fressin's upcoming Nature paper, the two planets will almost certainly be renamed Kepler-20e and Kepler-20f. |
根据2月份公布的数据以及戈蒂埃提交的有关主恒星特性的最新估计资料，情况应该是这样的：行星KOI-70.04的大小介于地球大小的80%至90%之间。至于行星KOI-70.05，除了其公转周期之外，一切数据均未公布。根据戈蒂埃的描述，KOI-70.05的公转周期为19.6天。几乎可以肯定的一点是，在弗雷桑即将发表于《自然》杂志上的论文中，这两颗行星将被重新命名为开普勒-20e和开普勒-20f。 |
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Earlier this week, Kepler scientists announced the discovery of Kepler-22b, a relatively large planet (2.4 Earth diameters) in the habitable zone of its parent star, where temperatures allow the existence of liquid water. With Kepler-20e, they have bagged a real Earth-sized planet, albeit much too close to its star to harbor life. It probably won't be too long before the planet hunters hit upon their Holy Grail: a planet just like Earth in the habitable zone of a sunlike star. Stay tuned. |
本周早些时候，开普勒望远镜项目的科学家们宣布，他们发现了一颗较大的行星——开普勒-22b。该行星相当于地球直径的2.4倍，对于其主恒星来说，它位于适合居住的区域上，上面的温度允许液态水的存在。尽管开普勒-20e距其主恒星太近，不可能拥有生命，但是有了该发现，科学家们算是真正地获得了一颗地球大小的行星。也许过不了多长时间，行星的搜寻者们就会找到最为理想的目标：恰似地球的行星位于类日恒星的可居住带上……让望远镜保持调谐状态，让我们拭目以待！ |
