Building a framework for robust biosignature identification on rocky exoplanets

在人类历史上，我们第一次达到了在系外行星大气中检测生物特征的技术能力。生物学是否是地球独有的这个问题是天文学、生物学、地质学和化学的交汇点。我的研究计划将在三个关键领域推动人们的理解，以帮助远程探测系外行星上的生物签名：1)恒星高能辐射和活动的影响，2)云如何影响观测和宜居性，以及3)探索假阳性生物签名的生成和消除歧义。所有这些领域都围绕着一个最重要的主题：我们如何才能有力地区分生命和非生命，即光年之外的生命？我的研究计划的一个关键目标是更好地了解恒星和行星之间的联系。最令人兴奋的宜居系外行星目标是围绕着耀斑恒星运行的恒星，比如距离我们最近的半人马座比邻星。然而，我们并不了解耀斑如何影响大气层和我们的观测结果。此外，对于凌日的宜居行星，将于2021年12月发射的詹姆斯·韦伯空间望远镜将需要增加多年的单独凌日观测，以建立探测大气特征所需的信号，我们不确定这些时间尺度上的大气特征是否存在可变性。我的研究计划将解决这一问题。我的团队将致力于的第二个领域是云对系外行星大气特征的影响。众所周知，云层会扰乱目前的系外行星观测。使用一维和三维建模工具，我的团队将学习更多关于不同大气和不同恒星辐射环境下的云的知识，以更好地理解未来的系外行星观测。我的程序将探索的第三个领域是如何审查未来的生物签名声明。生物签名检测的健壮性需要了解潜在的假阳性机制。氧是标志性的生物特征，有几种已知的假阳性机制，但我们仍然不知道大气逃逸可能与光化学有关。关于双重气体生物特征假阳性，也没有考虑大气压力的影响，特别是在耀斑或紫外线活跃的恒星周围。我的团队将帮助建立区分已知假阳性和真实生物签名检测的方法。我的研究计划之所以新颖，有两个原因--一个是我们将解决与用JWST解释第一次类地系外行星观测特别相关的问题，并解决潜在的简并解决方案。这项工作旨在回答基本问题，以了解未来的生物签名检测，并利用联合世界科学委员会和其他未来任务带来的机会。第二，我的研究项目也是高度多学科的。它将恒星天体物理学、系外行星大气模型、气候和地球生物学联系在一起。希望这将使我们更接近于回答“我们在宇宙中是孤独的吗？”这个古老的问题。

For the first time in human history, we are reaching the technological capability to detect biosignatures in the atmosphere of an exoplanet. This question of whether biology is unique to Earth lies at the intersection of astronomy, biology, geology and chemistry. My research program will drive forward understanding in three key areas to aid the remote detection of biosignatures on an exoplanet: 1) the impact of of a stars high energy radiation and activity, 2) how clouds affect observations and habitability, and 3) exploring false positive biosignature generation and disambiguation. All these areas centre around one overarching theme: how can we robustly distinguish life from non-life, light years away? One key target of my research program is to better understand the star-planet connection. The most exciting habitable exoplanet targets orbit flare stars, such as our nearest star, Proxima Centauri. However, we do not understand how flares impact atmospheres and our observations. Furthermore, for transiting habitable planets, the James Webb Space Telescope launching in December 2021 will need to add years of observations of separate transits to build up the signal required to detect atmospheric features, and we are unsure if there is variability in atmospheric features on those timescales. My research program will address this. A second area my group will work on is the impact of clouds on exoplanet atmosphere characterisation. Clouds are known to confound current exoplanet observations. Using 1D and 3D modelling tools, my group will learn more about clouds in different atmospheres and under different stellar radiation environments to better understand future exoplanet observations. The third area my program will explore is how to vet future biosignature claims. How robust a biosignature detection is requires an understanding of potential false positive mechanisms. There are several known false positive mechanisms for oxygen, the iconic biosignature, but we still don't know how atmospheric escape maybe linked with photochemistry. Nor has the influence of atmospheric pressure been looked at regarding a double gas biosignature false positive, particularly around flaring or UV active stars. My group will help establish ways for distinguishing known false positives from true biosignature detections. My research program is novel for two reasons - one is that we will tackle questions especially relevant for interpreting the first terrestrial exoplanet observations with JWST and address potential degenerate solutions. This work is designed to answer fundamental questions to understanding future biosignature detections and to capitalize on opportunities arising from JWST and other future missions. Two, my research program is also highly multidisciplinary. It links stellar astrophysics, exoplanet atmospheric modelling, climate, and geobiology. And hopefully, it will bring us closer to answering the age old question of "Are we alone in the Universe?"