【翻译】行星宜居性试验室对开普勒186F的描述

First Potentially Habitable Terran World
posted Apr 17, 2014, 10:59 AM by Abel Mendez Torres   [ updated Apr 17, 2014, 11:11 AM ]
Kepler-186 is a stellar system of five planets with an Earth-size world in the habitable zone.


Simulated comparison of a sunset on Kepler-186f and Earth. On Kepler-186f the star looks dimmer but slightly larger.

All the known potentially habitable exoplanets so far are superterran worlds (aka super-Earths) somewhat larger than Earth. The potential of life of these worlds is difficult to relate to Earth since there are no planets in the Solar System of comparable size and we know very little of them. Now a team of scientists led by Elisa V. Quintana from the SETI Institute and NASA Ames report the discovery of Kepler-186f, the first terran world (Earth-size) in the habitable zone of a star.

Kepler-186f has a similar size to Earth and it is most likely a rocky world. It orbits the M-dwarf star Kepler-186 along with four other inner planets, which are as old as the Solar System (>4 Gyr), in the constellation Cygnus 500 light years away. Kepler-186f receives less stellar flux (~32%) than presently does Mars (~43%). It could have a temperate climate if it has an atmosphere much denser than Earth. Even Earth probably experienced at least one episode of global glaciation with just a slightly lower stellar flux than today, 650 million years ago. However, early Mars had running surface liquid water with a similar stellar flux as Kepler-186f.

Kepler-186f was added to the Habitable Exoplanets Catalog with a low Earth Similarity Index (ESI) of 0.64 due to its potential colder climate. Still, it could be a more Earth-like world if it is experiencing a much higher greenhouse effect than Earth. Nevertheless, Kepler-186f is also the best candidate now of a rocky world in the habitable zone compared to the other known potentially habitable worlds.

                               
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原文地址：http://phl.upr.edu/press-release ... abitableterranworld

译文：
第一个可能适合适合人类居住的类地行星世界
由阿贝尔·门德斯·托雷斯发布于2014年4月17日上午10:59

开普勒-186是一个有五颗行星的恒星系统，其中一个行星与地球大小类似，并位于宜居带。

                               
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开普勒- 186F和地球的夕阳模拟比较。开普勒-186F的恒星看起来更暗，但稍大。

所有已知的可能适合人类居住的系外行星，到目前为止都是比地球稍微大一些的超级地球。这些世界可能存在的生物是很难与地球相联系的，因为在太阳系没有同等大小的行星，而且我们对它们（超级地球）所知甚少。现在，一支由SITI的Elisa V. Quintana和NASA Ames领导的科学家团队报告发现了开普勒- 186F ，第一颗位于宜居带的地球大小的行星。

开普勒- 186F有类似地球大小的体积，很有可能是一个类地行星。它与其他四颗内行星环绕的M级恒星开普勒-186旋转。这是一个和太阳系系统（> 40亿年）一样老的系统，位于500光年外的天鹅座。开普勒- 186F接受的恒星辐射通量（ 约32 ％ ）比火星目前接收的恒星辐射通量（约43 ％ ）更少 。但如果有比地球更稠密的大气，它就可能存在一个较为温和的气候。即使是地球，也可能因为6.5亿年前的较低恒星辐射通量，而遭遇过不止一次的全球性冰川期。此外，早期火星在与开普勒- 186F接受的恒星辐射通量相似时，也曾拥有流淌到在表面的液态水 。

开普勒- 186F已经列到系外宜居行星表之中，但由于其可能的寒冷气候，其地球相似度指标（ESI）仅有0.64，并不高 。不过，如果它正经历比地球强得多的温室效应，那就可能是一个更类似于地球的世界。然而，相对于其他已知的可能适合人类居住的星球，开普勒- 186F目前也是位于宜居带中的最可能的候选岩石行星。

                               
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Artistic representation of Kepler-186f as a cold world with shallow oceans as compared to Earth. Other possible interpretations of Kepler-186f are as a snowball frozen world (Hoth-like) or a dry cold world (Mars-like).
艺术家画出的开普勒-186f，相对于地球，这一个冰冷的世界，有着灰暗的海洋。此外，对于开普勒-186f可能的解读是一个冰冷的雪球（类似星球大战中的行星Huth），或者一个干冷的世界（类似火星）

                               
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开普勒-186和开普勒-62系统示意图，这两个系统的f行星接受的恒星辐射通量类似

                               
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对行星开普勒-186f的分析，它的温度可能只有192K，而火星则是210K。它被潮汐锁定的概率是50%。

                               
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行星宜居性试验室目前列出的21个疑似宜居系外行星

英文维基百科上说
Kepler-186f has a radius about 11% larger than that of Earth.Its mass and therefore density and composition are unknown; it could be a rocky terrestrial planet or a low density super-Earth or mini-Neptune with a thick atmosphere. However a massive hydrogen/helium atmosphere is thought to be unlikely in planets with radii below 1.5 R⊕. Red dwarfs emit a much stronger extreme ultraviolet (XUV) flux when young than later in life; the planet's primordial atmosphere would subject it to photoevaporation during that period, which would probably have largely removed any H/He-rich envelope through hydrodynamic mass loss. Mass estimates range from 0.32 M⊕ for a pure water/ice composition to 3.77 M⊕ if made up entirely of iron; a composition similar to Earth's (1/3 iron, 2/3 silicate rock) yields a mass of 1.44 M⊕.

Kepler-186f比地球半径大11%，它的质量和密度未知。它可能是一颗岩石行星，也可能是一颗低密度超级地球，或者是一颗有着厚重大气的迷你海王星。然而，在半径低于1.5倍地球半径的行星上，不太可能有大量的氢/氦大气层。红矮星在年轻时会释放出非常强的紫外线辐射。行星的原始大气在这个时期会接受这个辐射而造成光蒸发，使大气层中大量的氢和氦经由流体动力质量流失被剥离。行星的质量预测值从0.32地球质量（纯水/冰组成）到3.77地球质量（全部由铁组成），如果和地球的组成相同，其质量应该是1.44倍地球质量。

即便是岩石行星，质量密度和大气数据仍未知，如果这些数据和地球相差较大，2者生命形式差异会很大。

BlackEyeGalaxy 发表于 2014-4-19 14:03
即便是岩石行星，质量密度和大气数据仍未知，如果这些数据和地球相差较大，2者生命形式差异会很大。 ...

说实话，我对这个行星有生命的期望值不大。