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arXiv 1104.3756astro-ph.EP
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Gliese 581系统可居住性的大气研究

Atmospheric studies of habitability in the Gliese 581 system

P. von Paris, S. Gebauer, M. Godolt, H. Rauer, B. Stracke

摘要:

M-型恒星Gliese 581被至少一颗位于宜居带的类地行星候选者GL 581 d环绕。轨道模拟表明,GL 581的宜居带内的其他行星将是动态稳定的。最近,又有两颗候选行星被宣称存在,其中一颗位于宜居带。鉴于目前正在进行的M恒星周围行星的搜索,预计将导致许多潜在的可居住的超级地球的检测,我们以GL 581系统为例来调查这样的行星。与以前的GL 581系统的可居住性研究相比,我们使用一致的大气模型来评估地表条件和可居住性。此外,我们进行详细的大气模拟的一个更大的子集的潜在的行星和大气的情况比以前考虑的。一个一维辐射对流大气模式被用来计算模型大气的温度和压力分布,我们假设是由分子氮,水和二氧化碳。在这些计算中,诸如表面压力和CO2浓度以及轨道距离和行星质量等关键参数是不同的。结果意味着,在轨道距离为0.117天文单位时,可以获得高于冰点的地面温度,而与此处考虑的大气情景无关。对于0.146天文单位的轨道距离,二氧化碳浓度低至目前地球值的10倍就足以使地表温度高于水的冰点。在0.175 AU,只有5%和95%的CO2浓度的情况下被认为是宜居的。因此,GL 581系统中在先前确定的动力学稳定性范围内的额外超级地球行星将被认为是潜在的宜居行星。

英文摘要:

The M-type star Gliese 581 is orbited by at least one terrestrial planet candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown that additional planets inside the habitable zone of GL 581 would be dynamically stable. Recently, two further planet candidates have been claimed, one of them in the habitable zone. In view of the ongoing search for planets around M stars which is expected to result in numerous detections of potentially habitable Super-Earths, we take the GL 581 system as an example to investigate such planets. In contrast to previous studies of habitability in the GL 581 system, we use a consistent atmospheric model to assess surface conditions and habitability. Furthermore, we perform detailed atmospheric simulations for a much larger subset of potential planetary and atmospheric scenarios than previously considered. A 1D radiative-convective atmosphere model is used to calculate temperature and pressure profiles of model atmospheres, which we assumed to be composed of molecular nitrogen, water, and carbon dioxide. In these calculations, key parameters such as surface pressure and CO2 concentration as well as orbital distance and planetary mass are varied. Results imply that surface temperatures above freezing could be obtained, independent of the here considered atmospheric scenarios, at an orbital distance of 0.117 AU. For an orbital distance of 0.146 AU, CO2 concentrations as low as 10 times the present Earth's value are sufficient to warm the surface above the freezing point of water. At 0.175 AU, only scenarios with CO2 concentrations of 5% and 95% were found to be habitable. Hence, an additional Super-Earth planet in the GL 581 system in the previously determined dynamical stability range would be considered a potentially habitable planet.

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