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

在系外行星调查中，要寻找的关键生物特征之一是“植被红”，即波长> 700 nm的增强反射率，这在地球上意味着产氧光合作用。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纳米范围内的辐射有限，并且倾向于紫外线耀斑。但是，它们仍然可以维持生命。地球上的无氧光合自养生物利用暗淡的近红外光（800- 1000纳米），我们的生物圈充满了紫外线屏蔽和修复机制。因此，我们是否应该寻找奇怪的紫外线硬化，无氧生物圈的特征？这个理论项目将确定这些签名可能是什么。它将由理论生物光合作用学家克里斯·达菲（Chris Duffy，CD）监督，并由细菌光合作用专家康拉德·穆利诺（Conrad Mullineaux，CM）和天体物理学家托马斯·豪沃思（Thomas Howarth，TH）和爱德华·吉伦（Edward Gillen，EG）共同监督。目标1：利用CD和CM，学生将建立一个广义的光合作用系统模型，其中的子系统，如光捕获，光化学，修复等，形成一个代谢网络。这将根据可用光的光谱预测系统的反射特性，并将对已知的植物，藻类和细菌进行验证。目标二：通过CD、TH和EG，学生将模拟典型系外行星上可用的光谱，并相应地调整光合作用模型。在不考虑生物化学细节的情况下，我们将确定自我维持系统是否可行。目标三：利用CD、CM、TH和EG，学生将假设外生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各种例子以及化学和物理学普遍性的限制。其结果将是一个普遍的框架，了解光合作用，它与光的关系及其潜在的限制和可能性。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特征来为寻找太阳系外生命做出贡献。

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.