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Two Earth-sized planets orbiting Kepler-20

机译:两颗地球大小的行星绕开普勒20飞行

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摘要

Since the discovery of the first extrasolar giant planets around Sun-like stars, evolving observational capabilities have brought us closer to the detection of true Earth analogues. The size of an exoplanet can be determined when it periodically passes in front of (transits) its parent star, causing a decrease in starlight proportional to its radius. The smallest exoplanet hitherto discovered has a radius 1.42 times that of the Earth's radius (R_⊕), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03R_⊕) and the other smaller than the Earth (0.87R_⊕), orbiting the star Kepler-20, which is already known to host three other, larger, transiting planets. The gravitational pull of the new planets on the parent star is too small to measure with current instrumentation. We apply a statistical method to show that the likelihood of the planetary interpretation of the transit signals is more than three orders of magnitude larger than that of the alternative hypothesis that the signals result from an eclipsing binary star. Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate. The outer planet could have developed a thick water vapour atmosphere.
机译:自从发现第一个围绕类太阳恒星的太阳系外巨行星以来,不断发展的观测能力使我们更接近真正的地球类似物的探测。系外行星的大小可以在它周期性地经过其母恒星(途经),从而导致星光与其半径成正比减小时确定。迄今为止发现的最小系外行星的半径是地球半径(R_⊕)的1.42倍,因此是其体积的2.9倍。在这里,我们报告发现了两颗行星,它们绕着开普勒20星运行,一颗行星是地球大小(1.03R_⊕),另一颗小于地球(0.87R_⊕),该行星已知还拥有另外三颗更大的恒星行星。母星上新行星的引力拉力太小,无法用当前的仪器测量。我们使用一种统计方法来证明,行星对过渡信号的解释的可能性比信号由日蚀双星产生的替代假设的可能性大三个数量级。从理论上讲,这些行星是岩石,由铁和硅酸盐组成。外行星可能形成了浓厚的水蒸气气氛。

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  • 来源
    《Nature》 |2012年第7384期|p.195-198|共4页
  • 作者单位

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Department of Physics and Astronomy, San Jose State University, San Jose, California 95192, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Niels Bohr Institute, University of Copenhagen, DK-2100, Copenhagen, Denmark,Centerfor Star and Planet Formation, University of Copenhagen, DK-1350, Copenhagen, Denmark;

    NASA Exoplanet Science Institute/California Institute of Technology, Pasadena, California 91125, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Department of Astronomy and Astrophysics, University of California, Santa Cruz, California 95064, USA;

    Astronomy Department, University of Florida, Gainesville, Florida 32111, USA;

    Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California 91109, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Department of Astronomy, University of California, Berkeley, California 94720, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA,NASA Ames Research Center, Moffett Field, California 94035, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    Department of Astronomy, University of California, Berkeley, California 94720, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA;

    Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    SETI Institute/NASA Ames Research Center, Moffett Field, California 94035, USA;

    SETI Institute/NASA Ames Research Center, Moffett Field, California 94035, USA;

    NASA Ames Research Center, Moffett Field, California 94035, USA;

    SETI Institute/NASA Ames Research Center, Moffett Field, California 94035, USA;

    SETI Institute/NASA Ames Research Center, Moffett Field, California 94035, USA;

    Orbital Sciences Corporation/NASA Ames Research Center, Moffett Field, California 94035, USA;

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