Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life.
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life.
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DOI：
10.1089/ast.2017.1729
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发表时间：
2018-06
期刊：
影响因子：
4.2
通讯作者：
Lyons TW
中科院分区：
文献类型：
--
作者：
Schwieterman EW;Kiang NY;Parenteau MN;Harman CE;DasSarma S;Fisher TM;Arney GN;Hartnett HE;Reinhard CT;Olson SL;Meadows VS;Cockell CS;Walker SI;Grenfell JL;Hegde S;Rugheimer S;Hu R;Lyons TW
在未来的几年和几十年里，先进的太空和地面观测站将提供前所未有的机会来探测可能适合居住的系外行星的大气层和表面，以寻找生命的迹象。地球上的生命，通过其气态产物以及反射和散射特性，在我们星球的光谱上留下了自己的指纹。在物理和化学定律的普遍性的帮助下，我们转向地球生物圈，无论是在现在还是在地质时期，寻找有助于在其他地方寻找生命的模拟签名。考虑到从现代和古代地球获得的见解，以及更广泛的假设系外行星的可能性，我们编制了一份全面的概述，介绍了我们目前对潜在系外行星生物特征的理解，包括气体，表面和时间生物特征。我们还调查了生物光谱特征，这些特征在专业文献中是众所周知的，但尚未在系外行星生物特征的背景下得到有力的审查。我们简要地回顾了评估生物特征的可行性，包括确定化学不平衡的新方法，从远程可获得的数据和评估工具，以确定维持短寿命的生物源气体作为大气特征所需的最低生物量。我们特别关注自Des Marais等人的开创性综述以来所取得的进展。这项工作的目的不是提出新的生物特征策略，这是本系列中的同伴文章的目标，而是回顾当前的文献，在看似不同的领域之间建立有意义的联系，并为前进的道路扫清道路。关键词：系外行星-生物特征-适居性标记-光合作用-行星表面-大气层-光谱学-神秘生物圈-假阳性。天体生物学18，663-708。1.导言 1.1.生活要求 1.2.系外行星生物特征定义 1.3.生物特征类别2.评估行星适居性3.地外行星建模研究概述 3.1.地球观测 3.2.光谱模型 3.3.地球大气的光化学研究 3.4.穿越时空的地球4.气体生物特征 4.1.气体生物特征概述 4.2类地大气层 4.2.1.氧气（O2） 4.2.2.臭氧（O3） 4.2.3.甲烷（CH 4） 4.2.4.一氧化二氮（N2 O） 4.2.5.含硫气体（DMS、DMDS、CH 3SH）和与可检测的C2 H6的关系 4.2.6.氯甲烷（CH 3Cl） 4.2.7.作为生物特征的雾度 4.2.8.其他气体 4.3.生物O2/O3和可能的光谱鉴别器的“假阳性” 4.4.其他类型大气中的生物特征 4.5.宿主星星光谱对光化学的影响 4.6.耀斑和粒子事件对生物特征气体的影响 5.1.光合作用 5.1.1.光合作用原理 5.1.1.1.带隙波长与还原剂在生物气生成和色素颜色中的关系 5.1.1.2. OP的统一 5.1.2.光合色素和光养生物的颜色 5.1.2.1.结构 5.1.2.2.光吸收 5.1.3.植被“红边” 5.1.4.关于系外行星光合作用和色素特征的推测 5.2视网膜色素 5.3.其他表面生物特征：非光合色素和反射特征 5.4.假阳性表面生物特征 5.5.手性和极化生物特征 5.6.荧光和生物发光6.时间生物特征 6.1.大气气体的振荡 6.2.表面特征的振荡7.评估生物特征的可信度 7.1.化学不平衡 7.2.生物量估计 7.3.网络理论在生物签名中的应用8.神秘的生物圈：生命的“假阴性”？ 9.探测系外行星生物特征的前景
In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. Key Words: Exoplanets—Biosignatures—Habitability markers—Photosynthesis—Planetary surfaces—Atmospheres—Spectroscopy—Cryptic biospheres—False positives. Astrobiology 18, 663–708. 1. Introduction 1.1. Requirements for life 1.2. Exoplanet biosignature definitions 1.3. Biosignature categories 2. Evaluating Planetary Habitability 3. Overview of Terrestrial Exoplanet Modeling Studies 3.1. Observations of earth 3.2. Spectral models 3.3. Photochemical studies of terrestrial atmospheres 3.4. Earth through time 4. Gaseous Biosignatures 4.1. Gaseous biosignature overview 4.2. Earth-like atmospheres 4.2.1. Oxygen (O2) 4.2.2. Ozone (O3) 4.2.3. Methane (CH4) 4.2.4. Nitrous oxide (N2O) 4.2.5. Sulfur gases (DMS, DMDS, CH3SH) and relation to detectable C2H6 4.2.6. Methyl chloride (CH3Cl) 4.2.7. Haze as a biosignature 4.2.8. Other gases 4.3. “False positives” for biotic O2/O3 and possible spectral discriminators 4.4. Biosignatures in other types of atmospheres 4.5. Effects of the host star spectrum on photochemistry 4.6. Impacts of flares and particle events on biosignature gases 5. Surface Biosignatures 5.1. Photosynthesis 5.1.1. Principles of photosynthesis 5.1.1.1. Relationship between band gap wavelength and reductant in the generation of biogenic gases and pigment color 5.1.1.2. Uniqueness of OP 5.1.2. Photosynthetic pigments and the color of phototrophs 5.1.2.1. Structure 5.1.2.2. Light absorption 5.1.3. The vegetation “red edge” 5.1.4. Speculation about photosynthesis and pigment signatures on exoplanets 5.2. Retinal pigments 5.3. Alternative surface biosignatures: nonphotosynthetic pigments and reflectance features 5.4. False positive surface biosignatures 5.5. Chiral and polarization biosignatures 5.6. Fluorescence and bioluminescence 6. Temporal Biosignatures 6.1. Oscillations of atmospheric gases 6.2. Oscillations in surface signatures 7. Assessing Biosignature Plausibility 7.1. Chemical disequilibrium 7.2. Biomass estimation 7.3. Applications of network theory to biosignatures 8. Cryptic Biospheres: “False Negatives” for Life? 9. Prospects for Detecting Exoplanet Biosignatures 10. Summary
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影响因子：
5
作者：
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通讯作者：
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4.3
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