地球和太阳的镜像

地球和太阳的镜像

Among the more than 4,000 known exoplanets, KOI-456.04 is something special: less than twice the size of Earth, it orbits a Sun-like star. And it does so with a star-planet distance that could permit planetary surface temperatures conducive to life. The object was discovered by a team led by the Max Planck Institute for Solar System Research in Göttingen.

在4000多颗已知的系外行星中，KOI-456.04很特别:它的大小不到地球的两倍，它围绕着一颗类太阳的恒星运行。而且恒星与行星之间的距离可以使行星表面的温度有利于生命的存在。该物体是由位于哥廷根的马克斯·普朗克太阳系研究所领导的一个小组发现的。

Its host star, called Kepler-160, actually emits visible light; the central stars of almost all other exoplanets, on the other hand, emit infrared radiation, are smaller and fainter than the Sun and therefore belong to the class of red dwarf stars.

它的主星开普勒-160实际上是在发射可见光;另一方面，几乎所有其他系外行星的中心恒星都发出红外辐射，它们比太阳更小更弱，因此属于红矮星。

Space telescopes such as CoRoT, Kepler, and TESS have allowed scientists the discovery of about 4000 extrasolar planets (planets around distant stars) within the past 14 years. Most of these planets are the size of the gas giant planet Neptune, about four times the size of the Earth, and in relatively close orbits around their respective host stars.

在过去的14年里，诸如CoRoT、开普勒和TESS等太空望远镜已经让科学家们发现了大约4000颗太阳系外行星(围绕遥远恒星运行的行星)。这些行星中的大多数都是气态巨行星海王星的大小，大约是地球的四倍，它们围绕各自的主恒星运行的轨道相对较近。

But scientists have also discovered some exoplanets as small as the Earth that could potentially be rocky. And a handful of these small planets are also at the right distance to their host star to potentially have moderate surface temperatures for the presence of liquid surface water – the essential ingredient for life on Earth.

但科学家也发现了一些与地球一样小的系外行星，它们可能是岩石构成的。而且，这些小型行星中有一小部分与它们的主星距离合适，有可能拥有中等的表面温度，从而有可能存在液态水——这是地球上生命的必要成分。

“The full picture of habitability, however, involves a look at the qualities of the star too”, explains MPS scientist and lead author of the new study Dr. René Heller. So far, almost all exoplanets less than twice the size of Earth that have a potential for clement surface temperatures are in orbit around a red dwarf.

“然而，对可居住性的全面了解还需要考察恒星的质量”，新研究的主要作者，下院议员科学家雷内·海勒博士解释说。到目前为止，几乎所有体积小于地球两倍、表面温度可能温和的系外行星都在一颗红矮星的轨道上运行。

Red dwarf stars are known for their extremely long lifetimes. Life on an exoplanet in orbit around an old red dwarf star could potentially have had twice as much time than life on Earth to form and evolve. But the radiation from a red dwarf star is mostly infrared rather than visible light as we know it.

红矮星以其极其漫长的生命而闻名。在围绕一颗老红矮星运行的系外行星上，生命形成和进化的时间可能是地球上生命的两倍。但红矮星发出的辐射大多是红外线，而不是我们所知的可见光。

Many red dwarfs would later become habitable, with enhanced stellar luminosities as long as these stars are young. Moreover, their faintness requires any habitable planet to be so close to the star that the stellar gravity starts to deform the planet substantially.

许多红矮星后来变得适宜居住，只要这些恒星还年轻，它们的亮度就会增强。此外，它们的稀薄性要求任何宜居行星必须离恒星非常近，以至于恒星的引力开始使行星发生实质上的变形。

The resulting tidal heating in the planet could trigger fatal global volcanism. All things combined, the habitability of planets around red dwarf stars is heavily debated in the scientific community.

地球潮汐加热可能引发致命的全球火山活动。所有这些因素结合在一起，围绕红矮星的行星是否适合居住在科学界备受争议。