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arXiv 1608.06702astro-ph.EP
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寻找潜在可居住性的系外行星的相似性索引:对类火星世界的应用

Similarity indexing of exoplanets in search for potential habitability: application to Mars-like worlds

Madhu Kashyap Jagadeesh, S. B. Gudennavar, Urmi Doshi, M. Safonova

摘要:

对系外行星的研究是当前行星科学和天体生物学研究的主要目标之一。对来自CoRoT和开普勒等太空任务的大量行星数据的分析最终旨在找到一颗与地球相似的行星-地球的孪生兄弟,并回答潜在的外可居住性问题。地球相似性指数(ESI)是这一探索的第一步,范围从1(地球)到0(与地球完全不同)。它被定义为行星的四个物理参数:半径、密度、逃逸速度和地面温度。ESI又分为内部ESI(半径和密度的几何平均值)和表面ESI(逃逸速度和地面温度的几何平均值)。这里的挑战是确定哪些系外行星参数在发现这种相似性方面是重要的;进入内部ESI和表面ESI的各个参数对全球ESI的贡献如何。由于进入地面ESI的地面温度是不可观测的量,因此难以确定其值。利用太阳系天体的已知数据,建立了太阳系外行星表面温度与平衡温度之间的定标关系,设计了一种估算太阳系外行星地面温度的有效方法,并利用我们的图解方法进行了进一步的分析。一种名为火星相似性指数(MSI)的新方法被引入,以识别可能适合极端生命形式居住的行星。MSI定义在1(现在的火星)和0(与现在的火星不同)之间,并使用与ESI相同的物理参数。我们对类火星行星感兴趣,以寻找可能存在极端生命形式的行星,例如生活在地球极端环境中的生命形式;例如,火星上的甲烷可能是甲烷特有的极端生命形式代谢的产物。

英文摘要:

Study of exoplanets is one of the main goals of present research in planetary sciences and astrobiology. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth -- the Earth's twin, and answering the question of potential exo-habitability. The Earth Similarity Index (ESI) is a first step in this quest, ranging from 1 (Earth) to 0 (totally dissimilar to Earth). It was defined for the four physical parameters of a planet: radius, density, escape velocity and surface temperature. The ESI is further sub-divided into interior ESI (geometrical mean of radius and density) and surface ESI (geometrical mean of escape velocity and surface temperature). The challenge here is to determine which exoplanet parameter(s) is important in finding this similarity; how exactly the individual parameters entering the interior ESI and surface ESI are contributing to the global ESI. Since the surface temperature entering surface ESI is a non-observable quantity, it is difficult to determine its value. Using the known data for the Solar System objects, we established the calibration relation between surface and equilibrium temperatures to devise an effective way to estimate the value of the surface temperature of exoplanets for further analysis with our graphic methodology. A new approach, called Mars Similarity Index (MSI), is introduced to identify planets that may be habitable to the extreme forms of life. MSI is defined in the range between 1 (present Mars) and 0 (dissimilar to present Mars) and uses the same physical parameters as ESI. We are interested in Mars-like planets to search for planets that may host the extreme life forms, such as the ones living in extreme environments on Earth; for example, methane on Mars may be a product of the methane-specific extremophile life form metabolism.

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