Detectability of Life Using Oxygen on Pelagic Planets and Water Worlds
Donald M Glaser, Hilairy Ellen Hartnett, Steven J. Desch, Cayman T. Unterborn, Ariel Anbar, Steffen Buessecker, Theresa Fisher, Steven Glaser, Stephen R. Kane, … 展开作者
Donald M Glaser, Hilairy Ellen Hartnett, Steven J. Desch, Cayman T. Unterborn, Ariel Anbar, Steffen Buessecker, Theresa Fisher, Steven Glaser, Stephen R. Kane, Carey M. Lisse, Camerian Millsaps, Susanne Neuer, Joseph G. ORourke, Nuno Santos, Sara Imari Walker, Mikhail Zolotov
在系外行星上寻找生命是我们这个时代的重大科学挑战之一。迄今为止的战略是寻找（例如，通过像开普勒这样的凌日调查）在其恒星宜居带中的类地系外行星，然后使用透射光谱来测量行星大气中的生物特征气体，特别是氧气（例如，詹姆斯·韦伯太空望远镜（James Webb Space Telescope）这样的行星已经比JWST观测到的要多，像凌日系外行星调查卫星和其他任务将会发现更多。需要更好地了解与生物特征气体有关的地球化学循环，以便确定代价高昂的后续观测目标的优先次序，并帮助设计未来的飞行任务。我们定义了一个可探测性指数，以量化生物特征气体可以被分配为生物与非生物来源的可能性。我们应用这个指数的情况下，氧气，O2，类地行星上的水含量不同。我们证明，在类地系外行星上，水的重量百分比为0.2%（即，没有暴露的大陆）生物必需磷的减少的通量将光合作用产生的大气O2的输出限制到与通过水的光解加上氢逃逸的地球物理产生不可区分的水平。较高的水含量> 1wt%，导致高压冰盖进一步减缓磷循环。巧合的是，允许使用O2作为生物特征的最大含水量0.2wt%与基于质量和半径的无水一致。因此，O2生物特征的实用性可能需要直接检测行星上的水和陆地。
英文摘要：
The search for life on exoplanets is one of the grand scientific challenges of our time. The strategy to date has been to find (e.g., through transit surveys like Kepler) Earth-like exoplanets in their stars habitable zone, then use transmission spectroscopy to measure biosignature gases, especially oxygen, in the planets atmospheres (e.g., using JWST, the James Webb Space Telescope). Already there are more such planets than can be observed by JWST, and missions like the Transiting Exoplanet Survey Satellite and others will find more. A better understanding of the geochemical cycles relevant to biosignature gases is needed, to prioritize targets for costly follow-up observations and to help design future missions. We define a Detectability Index to quantify the likelihood that a biosignature gas could be assigned a biological vs. non-biological origin. We apply this index to the case of oxygen gas, O2, on Earth-like planets with varying water contents. We demonstrate that on Earth-like exoplanets with 0.2 weight percent (wt%) water (i.e., no exposed continents) a reduced flux of bioessential phosphorus limits the export of photosynthetically produced atmospheric O2 to levels indistinguishable from geophysical production by photolysis of water plus hydrogen escape. Higher water contents >1wt% that lead to high-pressure ice mantles further slow phosphorus cycling. Paradoxically, the maximum water content allowing use of O2 as a biosignature, 0.2wt%, is consistent with no water based on mass and radius. Thus, the utility of an O2 biosignature likely requires the direct detection of both water and land on a planet.
Theoretical Reflectance Spectra of Earth-Like Planets through Their Evolutions: Impact of Clouds on the Detectability of Oxygen, Water, and Methane with Future Direct Imaging Missions
Interior redox state effects on the stability of secondary atmospheres and observational manifestations: LP 791-18 d as a case study for outgassing rocky exoplanets
本研究以 LP 791-18 d 为例，耦合内部氧化还原状态与大气过程，揭示氧逸度对大气稳定性和观测特征的控制作用。
Characterizing Earth analogs may require a moderate or high-resolution spectrograph
University of California San Diego（加州大学圣地亚哥分校）；Space Telescope Science Institute（太空望远镜科学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Department of Astronomy & Astrophysics, University of California, Santa Cruz（加州大学圣克鲁兹分校天文与天体物理系）；University of California Observatories（加州大学观测台）；Department of Astronomy, California Institute of Technology（加州理工学院天文系）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Lunar & Planetary Laboratory, University of Arizona（亚利桑那大学月球与行星实验室）
