火星早期大气塌陷和大气再膨胀引起的甲烷释放
Methane release on Early Mars by atmospheric collapse and atmospheric reinflation
摘要：
早期火星河流的一个候选解释是由于表面释放的H $_2$或CH $_4$气体导致大气变暖。然而，目前还不清楚在一次事件中会释放多少气体。我们通过CH $_4$从包合物中快速释放的一种机制模拟CH $_4$释放。通过模拟CH $_4$ -笼形物释放如何受到火星的湿度和大气成分变化的影响，我们发现，CH $_4$笼形物的总释气的很大一部分发生在火星的第一次长期大气崩溃之后。这种大气崩溃引发的CH $_4$释放机制有三个阶段。(1)早期火星二氧化碳大气层的迅速崩溃引发了水冰从高地向两极的缓慢转移。(2)在随后的CO $_2$ -大气再膨胀和CO $_2$ -温室变暖时，低纬度包合物分解并释放甲烷气体。(3)然后甲烷会扰乱大气化学和地面温度，直到光化学过程破坏甲烷。在我们的模型中，我们发现在某些情况下，一个类似泰坦的薄雾层预计将形成，与早期火星表面上丰富的复杂非生物有机物的短暂沉积相一致。我们还发现，这种CH $_4$ -释放机制可以使早期火星变暖，但需要特殊的环境才能释放出10 $^{17}$ kg的CH $_4$，这是强烈变暖所需的最低限度。具体来说，只有当水合物稳定区最初被笼形物占据的比例超过10%时，以及当火星第一次长时间的大气崩溃发生在大气压力> 1巴时，才会发生强烈的变暖。
英文摘要：
A candidate explanation for Early Mars rivers is atmospheric warming due to surface release of H$_2$ or CH$_4$ gas. However, it remains unknown how much gas could be released in a single event. We model the CH$_4$ release by one mechanism for rapid release of CH$_4$ from clathrate. By modeling how CH$_4$-clathrate release is affected by changes in Mars' obliquity and atmospheric composition, we find that a large fraction of total outgassing from CH$_4$ clathrate occurs following Mars' first prolonged atmospheric collapse. This atmosphere-collapse-initiated CH$_4$-release mechanism has three stages. (1) Rapid collapse of Early Mars' carbon dioxide atmosphere initiates a slower shift of water ice from high ground to the poles. (2) Upon subsequent CO$_2$-atmosphere re-inflation and CO$_2$-greenhouse warming, low-latitude clathrate decomposes and releases methane gas. (3) Methane can then perturb atmospheric chemistry and surface temperature, until photochemical processes destroy the methane. Within our model, we find that under some circumstances a Titan-like haze layer would be expected to form, consistent with transient deposition of abundant complex abiotic organic matter on the Early Mars surface. We also find that this CH$_4$-release mechanism can warm Early Mars, but special circumstances are required in order to uncork 10$^{17}$ kg of CH$_4$, the minimum needed for strong warming. Specifically, strong warming only occurs when the fraction of the hydrate stability zone that is initially occupied by clathrate exceeds 10%, and when Mars' first prolonged atmospheric collapse occurs for atmospheric pressure > 1 bar.
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