类地行星凌日
Transits of Earth-Like Planets
摘要：
类地系外行星的透射光谱是一种潜在的适居性筛选工具。凌日行星是当今理解太阳系外行星的“罗塞塔石”，因为它们提供了描述巨行星大气的可能性，并且一旦被探测到，应该可以获得类地系外行星大气中的生物标志物。使用地球本身作为一个代理，我们展示了过境技术的潜力和局限性，以检测地球类似的系外行星过境的生物标志物。我们量化的地球的横截面作为波长的函数，并显示每个大气物种，气溶胶，和瑞利散射的影响。云对这幅图像没有显著影响，因为气溶胶和瑞利损失造成的低层大气不透明度超过云损失。我们计算的光谱特征的最佳信噪比的主要日食光谱的类地系外行星周围的类日恒星和M星，在太空中的6.5米望远镜。我们发现，所有重要的光谱特征的信号噪声值的顺序上的单位或更少的每个过境-除了最近的恒星-使得它很难检测到这样的功能，在一个单一的过境，这意味着共同添加的许多过境将是必不可少的。
英文摘要：
Transmission spectroscopy of Earth-like exoplanets is a potential tool for habitability screening. Transiting planets are present-day "Rosetta Stones" for understanding extrasolar planets because they offer the possibility to characterize giant planet atmospheres and should provide an access to biomarkers in the atmospheres of Earth-like exoplanets, once they are detected. Using the Earth itself as a proxy we show the potential and limits of the transiting technique to detect biomarkers on an Earth-analog exoplanet in transit. We quantify the Earths cross section as a function of wavelength, and show the effect of each atmospheric species, aerosol, and Rayleigh scattering. Clouds do not significantly affect this picture because the opacity of the lower atmosphere from aerosol and Rayleigh losses dominates over cloud losses. We calculate the optimum signal-to-noise ratio for spectral features in the primary eclipse spectrum of an Earth-like exoplanet around a Sun-like star and also M stars, for a 6.5-m telescope in space. We find that the signal to noise values for all important spectral features are on the order of unity or less per transit - except for the closest stars - making it difficult to detect such features in one single transit, and implying that co-adding of many transits will be essential.
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