A two-tiered approach to assessing the habitability of exoplanets.
A two-tiered approach to assessing the habitability of exoplanets.
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DOI：
10.1089/ast.2010.0592
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发表时间：
2011-12
期刊：
影响因子：
4.2
通讯作者：
D. Schulze‐Makuch;A. Méndez;A. Fairén;P. von Paris;C. Turse;Grayson Boyer;A. Davila;M. António;D. Catling;L. Irwin
中科院分区：
文献类型：
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作者：
D. Schulze‐Makuch;A. Méndez;A. Fairén;P. von Paris;C. Turse;Grayson Boyer;A. Davila;M. António;D. Catling;L. Irwin
在接下来的几年里，被编目的系外行星的数量将以数千计。这将极大地扩大潜在宜居世界的数量，并导致对它们的天体生物学潜力进行系统评估。在此，我们提出了系外行星宜居性的两级分类方案。第一层由地球相似性指数(ESI)组成，它允许根据世界与地球的相似性进行筛选，地球是目前唯一已知的有人居住的行星。ESI是基于大多数系外行星可用的或潜在可用的数据，如质量、半径和温度。对于分类方案的第二层，我们提出了行星宜居性指数(PHI)，该指数基于稳定底物的存在、可用能量、适当的化学物质和保持液体溶剂的潜力。PHI的设计是为了将我们所知的对生命的偏见搜索降至最低，并考虑到在更奇异的条件下可能存在的生命。因此，PHI需要比目前任何系外行星都更详细的知识。然而，未来的任务，如类地行星发现者，将收集这些信息并推进PHI。这两个指数的制定方式使它们的值能够随着技术和我们对宜居行星、卫星和生命进步的了解而更新。将所提出的测量方法应用于我们太阳系内的天体进行比较，发现了Gliese581系统中的两颗行星Gj581c和d，其ESI与火星相当，PHI介于木卫二和土卫二之间。
In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability. The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time. The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature. For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions. As such, the PHI requires more detailed knowledge than is available for any exoplanet at this time. However, future missions such as the Terrestrial Planet Finder will collect this information and advance the PHI. Both indices are formulated in a way that enables their values to be updated as technology and our knowledge about habitable planets, moons, and life advances. Applying the proposed metrics to bodies within our Solar System for comparison reveals two planets in the Gliese 581 system, GJ 581 c and d, with an ESI comparable to that of Mars and a PHI between that of Europa and Enceladus.