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探测生物特征的技术能力。生物是否是地球独有的这个问题是天文学、生物学、地质学和化学的交叉问题。我的研究计划将推动三个关键领域的理解，以帮助远程检测系外行星上的生物特征：1)恒星高能辐射和活动的影响，2)云如何影响观测和可居住性，以及3)探索假阳性生物特征的产生和消除歧义。所有这些领域都围绕着一个重要的主题：我们如何区分光年外的生命和非生命？我的研究计划的一个关键目标是更好地理解恒星-行星之间的联系。最令人兴奋的宜居系外行星是围绕耀斑恒星运行的，比如离我们最近的恒星比邻星。然而，我们不知道耀斑是如何影响大气和我们的观测的。此外，对于可居住的行星，2021年12月发射的詹姆斯·韦伯太空望远镜将需要增加对单独过境的多年观测，以建立探测大气特征所需的信号，我们不确定在这些时间尺度上大气特征是否存在变化。我的研究项目将解决这个问题。我的小组将研究的第二个领域是云对系外行星大气特征的影响。众所周知，云会干扰当前的系外行星观测。利用1D和3D建模工具，我的小组将更多地了解不同大气和不同恒星辐射环境下的云，以更好地了解未来的系外行星观测。我的项目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。氧气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如何与光化学联系起来。大气压力对双气体生物特征假阳性的影响也没有被研究，特别是在耀斑或紫外线活跃的恒星周围。我的小组将帮助建立区分已知的假阳性和真正的生物特征检测的方法。我的研究计划是新颖的，有两个原因——一个是我们将解决问题，特别是与解释JWST的第一个类地系外行星观测和解决潜在的简并解决方案相关的问题。这项工作旨在回答理解未来生物特征检测的基本问题，并利用来自JWST和其他未来任务的机会。第二，我的研究项目也是高度跨学科的。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起来。希望它能让我们更接近于回答这个古老的问题：“我们在宇宙中是孤独的吗？”

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?"