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On Earth, strange things, including frogs and fish, sometimes fall from the sky, but on a distant extrasolar planet, the weather could be even weirder: When a front moves in, small rocks rain down on the surface, a new study suggests. |
地球上存在奇怪的事情——有时包括青蛙和鱼在内的动物从天而降。然而一项新研究表明：在一颗遥远的系外行星上，天气状况更加不可思议——当锋面到来时，小块岩石就会降落到行星表面上。 |
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The exoplanet, COROT-7b, was discovered in February by the COROT space telescope launched by the French and European space agencies. Last month it became the first planet outside our solar system to be confirmed as a rocky body — most other known exoplanets are gas giants. |
2月份，法国和欧洲宇航局联合发射的COROT太空望远镜发现了系外行星COROT-7b。上个月，该行星成为太阳系以外第一颗有待证实的岩石行星，多数已知的其他系外行星都是气态的巨型行星。 |
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The planet is nearly twice the size of Earth and about five times the mass of our world. Calculations have indicated it has a density about that of Earth's, which means it is likely made up of silicate rocks, just as Earth's crust is. |
这颗行星的大小是地球的将近两倍，质量大约是我们地球的5倍。计算显示，该行星的密度大约跟地球相当，这意味着它可能是由硅酸盐岩石构成的，恰似地壳中的成分。 |
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The planet is likely much less hospitable to life though, as it is only about 1.6 million miles (2.6 million km) away from its parent star — 23 times closer than Mercury sits to the sun. |
然而，这颗行星不大可能适于生命生存，因为它距其主恒星仅约160万英里（260万公里），比水星距太阳近23倍。 |
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Locked and scorching |
引力束缚与灼热的温度 |
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Because the planet is so close to the star, it is gravitationally locked to it in the same way the Moon is locked to Earth. One side of the planet always faces its star, just as one side of the Moon always faces Earth. |
由于这颗行星距其恒星太近，引力把它束缚在恒星周围，就如同月球被束缚在地球周围一样。这颗行星总是由相同的一面朝向其主恒星，正如月球总是由相同的一面朝向地球一样。 |
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This star-facing side has a temperature of about 4,220 degrees Fahrenheit (2,326 degrees Celsius) — hot enough to vaporize rock. So unlike the much cooler Earth, COROT-7b has no volatile gases (carbon dioxide, water vapor, nitrogen) in its atmosphere. Instead its atmosphere consists of what might be called vaporized rock. |
朝向恒星的那一面温度大约为4,220华氏度（2,326摄氏度），足以将岩石蒸发掉。地球的温度要低得多，因此COROT-7b跟地球不同，它的大气中没有漂浮的气体（如：二氧化碳、水汽、氮等），其大气是由可以称之为“汽化的岩石”构成的。 |
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"The only atmosphere this object has is produced from vapor arising from hot molten silicates in a lava lake or lava ocean," said Bruce Fegley Jr., of Washington University in St. Louis. |
“这颗天体上唯一的一种大气产生于炽热的液态硅酸盐散发出的蒸气，这种硅酸盐存在于熔岩湖或熔岩海里，”华盛顿大学圣路易斯分校的布鲁斯·费格雷说。 |
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Rocky weather forecast |
岩石天气预测 |
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To find out what COROT-7b's atmosphere might be like, Fegley and his colleagues modeled it. They found that COROT-7b's atmosphere is made up of the ingredients of rocks and when "a front moves in," pebbles condense out of the air and rain into lakes of molten lava below. |
为了搞清COROT-7b大气的情况，费格雷及同事对此进行了模拟。他们发现，COROT-7b的大气是由岩石成分构成的，当锋面来临时，小石子从空气中冷凝出来，降落到下面的熔岩湖中。 |
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"Sodium, potassium, silicon monoxide and then oxygen — either atomic or molecular oxygen — make up most of the atmosphere," Fegley said. But there are also smaller amounts of the other elements found in silicate rock, such as magnesium, aluminum, calcium and iron. |
“钠、钾、一氧化硅和氧（原子氧或分子氧）构成了大气的主要成分，”费格雷说。但是，在硅酸盐岩石中还有少量的其他成分，如：镁、铝、钙和铁。 |
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The rock rains form similarly to Earth's watery weather: "As you go higher the atmosphere gets cooler and eventually you get saturated with different types of 'rock' the way you get saturated with water in the atmosphere of Earth," Fegley explained. "But instead of a water cloud forming and then raining water droplets, you get a 'rock cloud' forming and it starts raining out little pebbles of different types of rock." |
岩石雨的形成类似于地球上的雨水天气。“越是在高处，大气的温度就越低，最终大气中的各种岩石处于饱和状态，就跟地球大气中的水分处于饱和状态时一样，”费格雷解释说，“但是，那里的大气饱和时形成的不是水云，因而降落的也不是雨水；那里的大气饱和之后形成的是‘岩石云’，然后开始降落各种不同的小石子。” |
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Menagerie of minerals |
五花八门的矿物 |
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The exoplanet's atmosphere condenses out minerals such as enstatite, corundum, spinel, and wollastonite. |
这颗系外行星的大气冷凝后产生矿物，如：顽火辉石、刚玉、尖晶石和硅灰石。 |
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Elemental sodium and potassium, which have very low boiling points in comparison with rocks, do not rain out but would instead stay in the atmosphere, where they would form high gas clouds buffeted by the stellar wind from COROT-7. These large clouds may be detectable by Earth-based telescopes. The sodium, for example, should glow in the orange part of the spectrum, like a giant but very faint sodium vapor streetlamp. |
跟岩石相比，钾和钠两种元素的沸点要低得多，因而不会以雨的形式降落下来。相反，两种元素滞留在大气中，形成高空气云，受到来自恒星COROT-7的星风的冲击。这些大团的气云可以被地面望远镜探测到。例如，钠在光谱中呈现出橙色光，就象一盏巨大而非常暗淡的钠汽灯。 |
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Observers have recently spotted sodium in the atmospheres of two other exoplanets. |
最近，观察人员在其他的两颗系外行星上也发现了钠。 |
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The new modeling finding is detailed in the Oct. 1 issue of The Astrophysical Journal. |
这次新模拟所发现的情况详细地记录在10月1日出版的《天体物理学杂志》上。 |
