The origin of RNA precursors on exoplanets.
The origin of RNA precursors on exoplanets.
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DOI：
10.1126/sciadv.aar3302
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发表时间：
2018-08
期刊：
影响因子：
13.6
通讯作者：
Queloz D
中科院分区：
文献类型：
--
作者：
Rimmer PB;Xu J;Thompson SJ;Gillen E;Sutherland JD;Queloz D
研究人员确定了一个“自然发生区”，在该区域之外，生命的组成部分无法通过光化学形成。鉴于生命的大分子构件很可能是在紫外线 (UV) 存在下通过光化学产生的，我们确定了一些关于哪些恒星为这种光化学产生足够的紫外线的一般限制。我们通过实验测量紫外线化学（“光化学”，益生元合成所需）的速率常数与在没有紫外线的情况下发生的双分子反应（“暗化学”）的速率常数来估计紫外线光化学需要多少光。我们对涉及 HS− 的代表性光化学反应进行这些测量。通过平衡光化学和暗化学的速率，我们根据不同恒星类型的恒星的紫外线通量是否足以建立这种大分子益生元库存来描绘其周围的“自然发生区”。我们发现光化学反应的速度足够快，足以为比 K5（4400 K）更热的恒星建立前生命体库存。我们展示了自然发生区如何与液态水宜居区重叠。如果比 K5 温度低的恒星非常活跃，它们也可能会推动这些构件的形成。 HS− 光化学反应太慢，即使对于早期地球也无法发挥作用。
Researchers identify an “abiogenesis zone,” outside of which the building blocks of life cannot form photochemically. Given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (UV) light, we identify some general constraints on which stars produce sufficient UV for this photochemistry. We estimate how much light is needed for the UV photochemistry by experimentally measuring the rate constant for the UV chemistry (“light chemistry”, needed for prebiotic synthesis) versus the rate constants for the bimolecular reactions that happen in the absence of the UV light (“dark chemistry”). We make these measurements for representative photochemical reactions involving and HS−. By balancing the rates for the light and dark chemistry, we delineate the “abiogenesis zones” around stars of different stellar types based on whether their UV fluxes are sufficient for building up this macromolecular prebiotic inventory. We find that the light chemistry is rapid enough to build up the prebiotic inventory for stars hotter than K5 (4400 K). We show how the abiogenesis zone overlaps with the liquid water habitable zone. Stars cooler than K5 may also drive the formation of these building blocks if they are very active. The HS− light chemistry is too slow to work even for early Earth.