标题： 土卫六大气变化建模：流星体进入的流体力学和冲击诱导化学反应 显示英文标题

标题： Modeling Atmospheric Alteration on Titan: Hydrodynamics and Shock-Induced Chemistry of Meteoroid Entry

摘要： 流星体进入行星大气层会产生弓形激波，导致高温气体条件，从而驱动化学反应。 在本文中，我们使用Athena++代码对流星体进入进行三维流体动力学模拟，并通过Cantera进行化学计算，以模拟由大气进入引发的非平衡化学反应。 我们的气动模拟揭示了复杂激波结构的形成，包括次级激波，这些结构影响气体介质的热力学演化。 通过沿流线跟踪热力学参数，我们分析了激波加热和随后的膨胀冷却对化学反应路径的影响。 我们的结果表明，当冷却时间尺度超过反应速率时会发生化学淬火，导致形成与平衡预测不同的化学产物。 我们表明，分子合成的效率取决于物体\textquotesingle 的大小和速度，这会影响进入后的气体混合物的组成。 将我们的模型应用于土卫六，我们证明有机物质可以在土卫六当前环境中合成。 此外，我们发现氮气，作为主要的大气成分，保持稳定，而水蒸气被有效去除，这一结果与平衡化学假设不一致。 而且，我们将模拟结果与激光实验进行比较，发现化学产率有良好的一致性。 最后，我们还评估了流星体进入对土卫六\textquotesingle 大气的整体影响，表明流星体进入事件可能在早期土卫六\textquotesingle 历史中起到了提供HCN等分子的重要作用。 显示英文摘要

摘要： Meteoroid entry into planetary atmospheres generates bow shocks, resulting in high-temperature gas conditions that drive chemical reactions. In this paper, we perform three-dimensional hydrodynamic simulations of meteoroid entry using the Athena++ code, coupled with chemistry calculations via Cantera to model the non-equilibrium chemistry triggered by atmospheric entry. Our aerodynamical simulations reveal the formation of complex shock structures, including secondary shock waves, which influence the thermodynamic evolution of the gas medium. By tracking thermodynamic parameters along streamlines, we analyze the effects of shock heating and subsequent expansion cooling on chemical reaction pathways. Our results demonstrate that chemical quenching occurs when the cooling timescale surpasses reaction rates, leading to the formation of distinct chemical products that deviate from equilibrium predictions. We show that the efficiency of molecular synthesis depends on the object\textquotesingle s size and velocity, influencing the composition of the post-entry gas mixture. Applying our model to Titan, we demonstrate that organic matter can be synthesized in the present environment of Titan. Also, we find that nitrogen, the dominant atmospheric component, remains stable, while water vapor is efficiently removed, a result inconsistent with equilibrium chemistry assumptions. Moreover, we compare our simulation results with laser experiments and find good agreement in chemical yields. Finally, we also evaluate the impact on Titan\textquotesingle s atmosphere as a whole, showing that meteoroid entry events could have played a significant role in supplying molecules such as HCN during early Titan\textquotesingle s history.