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Since prehistoric times, people have watched the moon waxing and waning through its phases. Four hundred years ago, Galileo was the first to observe similar phases of the planet Venus. Now, for the first time, astronomers have seen the changing phases of a planet outside of our solar system. They expect similar observations in the future to reveal important details about the atmosphere, cloud cover, and climate of planets orbiting other stars. |
自从史前的年代，人们就开始通过月相观察月球的盈亏。四百年前，伽利略第一次观察到金星具有类似的相位。现在，天文学家们第一次观察到我们太阳系以外一颗行星的不断变化的相位，他们期望将来可以利用同样的观察来揭示其他恒星周围的行星上有关大气、云量和气候的重要详细情况。 |
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Most extrasolar planets (or exoplanets for short) can't be seen directly, especially if they are very close to their parent stars; astronomers see only the combined light of the star and the planet. Sometimes, they happen to see the orbits of exoplanets edge-on. In those cases, the planet alternately shows more of its dayside and then more of its nightside as it circles its star. These phases should show up as tiny variations in the intensity of the observed light, researchers have predicted. |
多数太阳系以外的行星（简称“系外行星”）不能被直接观察到，特别是当距离其主恒星太近的时候，情况更是如此，天文学家们只能观察到来自恒星和行星的混合光线。有时，天文学家们碰巧从侧面观察到系外行星的轨道，在这种情况下，行星在围绕恒星旋转的时候就会交替地呈现出有时光面较多、有时暗面较多。研究人员预计，这些相位应该表现为所观测到的光线在亮度上的微弱变化。 |
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Astronomers Ignas Snellen of Leiden Observatory in the Netherlands and colleagues have now demonstrated that such optical observations are feasible. The researchers scanned publicly available data on a star known as CoRoT-1, which is 1600 light-years away. In the numbers, they found minute periodic variations in brightness that they believe are caused by the changing phases of its gaseous giant planet, known as CoRoT-1b. |
现在，荷兰莱顿天文台的天文学家伊格纳斯·斯奈伦及同事证明了这样的光学观测是可行的。研究人员仔细查看了有关一颗恒星的可以公开使用的资料，该恒星叫做CoRoT-1，位于1600光年之外。在诸多数据中，研究人员发现了在亮度上存在周期性的细微变化，他们认为这些变化是由于其巨大的气态行星不断变化的相位造成的，该行星叫做CoRoT-1b。 |
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Because it is less than 5 million kilometers from its parent star, the planet's dayside temperature is about 2000°C, and part of the planet's light is probably thermal glow instead of reflected star light. But, says Snellen, "even if we assume that the observed brightness variation is fully due to reflected star light, we find that the planet's reflectivity is probably lower than 10%." That's much less than the reflectivity of Jupiter, indicating that CoRoT-1b probably lacks extensive clouds. The team reports its results tomorrow in Nature. |
由于距离其主恒星不到500万公里，该行星的光面温度大约为2000摄氏度，而且部分光线很可能是热释光，而不是反射自恒星的光线。然而，斯奈伦称：“即使假定所观察到的光线完全源于反射自恒星的光，我们仍然发现该行星的反射率很可能不到10%。”这比木星的反射率要低得多，表明行星CoRoT-1b很可能缺少大范围的云层。研究小组在明天的《自然》杂志上报道了他们的研究成果。 |
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"It's a trailblazing result," says astrophysicist Sara Seager of the Massachusetts Institute of Technology in Cambridge. In this pioneering case, the measurements aren't precise enough yet for a detailed analysis of CoRoT-1b, she says, but knowing a planet's reflectivity is key to learning about its cloud cover and climate. "It heralds an interesting new way to characterize planets." |
“这是一项开创性的成果，”麻省理工学院的天体物理学家萨拉·西格指出。她说：在这项具有先导性的研究中，所利用的测量数据还不够准确，还无法对行星CoRoT-1b进行详细的分析，但搞清一颗行星的反射率对于了解其云量和气候是很关键的。“这预示着找到了一个可以用来分析行星特征的有趣的新方法。” |
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NASA's Kepler satellite, launched in March, will probably reveal many more phase-changing exoplanets, and so might the newly refurbished Hubble Space Telescope and even large, ground-based telescopes. "If it can be done for this planet, you can do it for other systems too," says astronomer Heather Knutson of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "Someday, this kind of observation will become commonplace." |
美国国家航空航天管理局的开普勒人造卫星于3月份发射升空，很可能将会揭示更多具有相位变化的系外行星。整修一新的哈勃太空望远镜，甚至还有大型的地面望远镜都可能会发现这样的系外行星。“如果能够对这颗行星进行这样的观测，那么这种观测对其他的行星系统也能够行得通，”马萨诸塞州剑桥市哈佛-史密森天体物理中心的天文学家希瑟·克努森说，“有朝一日，这种观测将会得到普遍运用。 |
