NCAS Climate, University of Reading, Reading, UK.
Astrobiology. 2012 Jan;12(1):3-8. doi: 10.1089/ast.2011.0668. Epub 2011 Dec 19.
M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought.
M 星约占主序星的 80%，因此它们的行星系统为寻找类地行星（即那些具有表面液态水的行星）提供了最佳机会。我们利用地球冰冻圈的光谱分辨数据，为围绕两颗观测到的红矮星（或 M 星）运行的模拟行星表面建模，模拟了水冰的宽带反照率或反射率。在大于 1μm 的波长处，雪和冰的反照率逐渐降低，而 M 星在这些相同的较长波长处辐射出相当一部分辐射，这意味着围绕 M 星运行的行星上的冰和雪的反照率远低于地球的反照率。我们的研究结果表明，与围绕 G 型恒星（如太阳）运行的行星相比，围绕 M 星运行的行星上的冰/雪反照率气候反馈要弱得多。此外，如果考虑到冰冻圈反照率的光谱变化，具有大量冰和雪覆盖的行星在给定恒星通量下的表面温度将显著升高，这反过来又意味着围绕 M 星的宜居带的外边缘可能比之前认为的要离母星远 10-30%。
