太阳系外较冷的以氢为主的行星的热化学和光化学：GJ436b的情况
Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b
摘要：
介绍了一种新的热化学动力学和光化学模型。我们使用高温双向反应速率进行重要的H、C、O和N反应（最重要的是CH $_4$到CO的相互转化），使我们能够在大气深处纯动力学地实现热化学平衡。这使得从头化学建模的整个大气，从深大气热化学平衡的光化学为主的制度。我们使用我们的模型来探索较冷的（$T_{eff} < 10^3$ K）太阳系外巨行星的大气化学。特别是，我们选择模拟附近的热海王星GJ 436 b，唯一的行星在这个温度制度，光谱测量和化学丰度的估计，现在存在。最近的{ \it Spitzer}测量与检索表明，甲烷被强烈驱动的平衡，并在GJ 436 b的向阳面深度耗尽，而淬灭的一氧化碳是丰富的。这是令人惊讶的，因为GJ 436 b是冷却器比许多严重照射热木星和热有利于CH $_4$，因此需要一个有效的机制来摧毁it. We包括现实的估计紫外线通量从母dM星GJ 436，约束直接光解和光敏耗尽CH $_4$。虽然我们的模型表明，在较冷的系外行星中，在一系列行星金属丰度范围内，可能存在相当丰富的不平衡条件，但我们无法产生CH $_4$大量破坏的条件。一种可能性是在0.01-1巴之间有大量的H原子（它们攻击CH $_4$）的异常来源，但我们还不能确定产生这些热原子的有效方法。
英文摘要：
We introduce a new thermochemical kinetics and photochemical model. We use high-temperature bidirectional reaction rates for important H, C, O and N reactions (most importantly for CH$_4$ to CO interconversion), allowing us to attain thermochemical equilibrium, deep in an atmosphere, purely kinetically. This allows ab initio chemical modeling of an entire atmosphere, from deep-atmosphere thermochemical equilibrium to the photochemically dominated regime. We use our model to explore the atmospheric chemistry of cooler ($T_{eff} < 10^3$ K) extrasolar giant planets. In particular, we choose to model the nearby hot Neptune GJ436b, the only planet in this temperature regime for which spectroscopic measurements and estimates of chemical abundances now exist. Recent {\it Spitzer} measurements with retrieval have shown that methane is driven strongly out of equilibrium and is deeply depleted on the dayside of GJ 436b, whereas quenched carbon monoxide is abundant. This is surprising because GJ 436b is cooler than many of the heavily irradiated hot Jovians and thermally favorable for CH$_4$, and thus requires an efficient mechanism for destroying it. We include realistic estimates of ultraviolet flux from the parent dM star GJ 436, to bound the direct photolysis and photosensitized depletion of CH$_4$. While our models indicate fairly rich disequilibrium conditions are likely in cooler exoplanets over a range of planetary metallicities, we are unable to generate the conditions for substantial CH$_4$ destruction. One possibility is an anomalous source of abundant H atoms between 0.01-1 bars (which attack CH$_4$), but we cannot as yet identify an efficient means to produce these hot atoms.
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