Photosynthesis on Alien Worlds: What might it look like, and can it be detected?

在系外行星调查中，需要寻找的关键生物特征之一是“植被退缩”，这是一种在波长&gt；700 nm处反射率增强的现象，在地球上，这标志着产氧光合作用。不幸的是，大多数已知的系外行星围绕着小恒星运行，在400-700纳米范围内发射有限，并有紫外线耀斑的趋势。然而，它们可能仍然支撑着生命。地球上的无氧光自养生物利用微弱的近红光(800-1000 nm)，我们的生物圈充满了紫外线屏蔽和修复机制。因此，我们应该寻找奇怪的紫外线硬化、缺氧生物圈的特征吗？这个理论项目将确定这些标志可能是什么。它将由理论生物物理学家克里斯·达菲(CD)、细菌光合作用专家康拉德·穆利诺(CM)、天体物理学家托马斯·豪沃斯(TH)和爱德华·吉伦(EG)共同监督。目标1：使用CD和CM，学生将创建一个广义的光合作用系统模型，在该模型中，光收集、光化学、修复等子系统形成非代谢网络。这将根据可用光的光谱来预测系统的反射特性，并将针对已知的植物、藻类和细菌进行验证。目标2：学生将用CD、TH和EG模拟典型系外行星上的光能谱，并相应地调整光合作用模型。在不担心生化细节的情况下，我们将确定一个自我维持系统是否可行。目标3：使用CD、CM、TH和EG，学生将假设外光合作用模型的生化实现，并模拟其潜在的反射特征。这受到地球光合作用的不同例子以及化学和物理的普遍性的限制。其成果将是理解光合作用、光合作用与光的关系以及光合作用的潜在限制和可能性的通用框架。通过探索极端环境中光合作用的新形式，我们可以通过提出新的目标生物签名来为寻找太阳外生命做出贡献。

In exoplanet surveys one of the key biosignatures to look for is the 'vegetation rededge', an enhanced reflectance at wavelengths >700nm, which on Earth signifiesoxygenic photosynthesis. Unfortunately, most known exoplanets orbit small stars withlimited emission in the 400-700nm range and tendency towards UV flaring. However,they might still support life. Earth's anoxygenic photoautotrophs exploit dim, nearinfraredlight (800-1000nm) and our biosphere is full of UV screening and repairmechanisms. Should we therefore be searching for signatures of strange UV-hardened,anoxygenic biospheres? This theoretical project will establish what these signaturesmight be. It will be supervised by theoretical biophysicist Chris Duffy (CD) and cosupervisedby bacterial photosynthesis expert Conrad Mullineaux (CM) andAstrophysicists Thomas Howarth (TH) and Edward Gillen (EG). Objective 1: With CDand CM the student will create a generalized systems model of photosynthesis, inwhich subsystems such as light-harvesting, photochemistry, repair, etc. form ametabolic network. This will predict the reflectance properties of the system based onthe spectrum of available light, and will be validated against known plants, algae, andbacteria. Objective 2: With CD, TH and EG the student will model the spectrum of lightavailable on typical exoplanets and adjust the photosynthetic model accordingly.Without worrying about biochemical details, we will determine whether a selfsustainingsystem is feasible. Objective 3: With CD, CM, TH and EG the student willhypothesize on biochemical realizations of the exo-photosynthesis model and simulatetheir potential reflectance signatures. This is constrained by diverse examples of Earthphotosynthesis and the universality of chemistry and physics. The outcome will be ageneralized framework for understanding photosynthesis, its relationship to light andits potential limits and possibilities. By exploring novel forms of photosynthesis inextreme environments, we can contribute to the search for extra-solar life byproposing new target bio-signatures.