A hydrocode calculation coupled with reaction kinetics of carbon compounds within an impact vapor plume and its implications for cometary impacts on Galilean satellites
A hydrocode calculation coupled with reaction kinetics of carbon compounds within an impact vapor plume and its implications for cometary impacts on Galilean satellites
复制标题
DOI：
10.1016/j.icarus.2010.06.016
复制
发表时间：
2010-11-01
期刊：
影响因子：
3.2
通讯作者：
Matsui, Takafumi
中科院分区：
文献类型：
--
作者：
Ishimaru, Ryo;Senshu, Hiroki;Matsui, Takafumi
通过撞击蒸气羽流中的化学反应合成有机分子被认为是在行星上提供有机物的一种机制。然而，在快速膨胀的蒸气羽流或反应的淬灭过程中的化学反应的动力学尚未被广泛研究。在这项研究中，我们构建了一个新的数值模型，计算动力学的整个化学反应的冲击蒸汽羽。数值结果表明，到目前为止，提出的半解析模型，其中的化学物种的最终数量是由涉及物种的最快反应路径的淬火温度下的平衡丰度给出，低估了有机分子的产率，如HCN，高达10倍。这是因为先前使用的假设，即一种物质可以通过涉及该物质的最快反应路径与反应系统的其余部分达到平衡，不一定有效。我们对高温H/C/N/O反应系统的分析表明，慢反应的淬灭将反应网络分成与反应系统的其余部分隔离的较小的反应子系统。然后，最快的反应路径不能使孤立的反应子系统与反应系统的其余部分平衡。模拟这种实际的不平衡机制需要同时对整个反应网络进行数值计算，这相当于进行完整的动力学模型计算，例如我们的模型。我们的数值代码使得有可能定量地讨论各种情况下的撞击化学，如伽利略卫星。在这项研究中，我们的数值模型被应用到通过彗星撞击伽利略卫星的有机分子的交付。我们的数值计算结果表明，小粒子的影响，将产生HCN有效。生成的HCN可能会立即冻结并沉积在卫星表面，在那里它可能最终通过带电粒子的照射转化为复杂的有机物。另一方面，大规模的影响可能会形成短暂的CH 4-N-2大气，其中复杂的有机物（托林）可能会通过能量沉积的紫外线和/或带电粒子。由此产生的复杂有机物可能随后沉淀在卫星表面，与撞击坑的位置没有明确的相关性。这种分布的复杂的有机物产生的化学反应蒸汽羽流由于彗星的影响，可以解释吸收（4.57 μ m）伽利略卫星nonassociated可观察到的（中型和大型）的影响陨石坑。(C)2010年爱思唯尔公司All rights reserved.
The synthesis of organic molecules via chemical reactions within impact vapor plumes has been proposed as a mechanism to supply organics on a planet. However, the kinetics of chemical reactions within a rapidly expanding vapor plume or quenching process of the reactions has not been studied extensively. In this study, we constructed a new numerical model that calculates kinetics of the entire chemical reactions within an impact vapor plume. Numerical results revealed that the semi-analytical models proposed so far, in which the final amount of a chemical species was given by the equilibrium abundance at the quenching temperature of the fastest reaction path involving the species, underestimates the yield of organic molecules, such as HCN, by up to a factor of 10. This is because the previously used assumption that a species can achieve equilibrium with the rest of the reaction system via the fastest reaction path involving the species is not necessarily valid. Our analysis of the high-temperature H/C/N/O reaction system suggests that the quenching of slow reactions divides the reaction network into smaller reaction subsystems isolated from the rest of the reaction system. Then, the fastest reaction path cannot equilibrate an isolated reaction sub-system with the rest of the reaction system. Simulation of this actual disequilibrium mechanism requires a simultaneous numerical calculation of the entire reaction network, which is equivalent to conducting a full kinetic model calculation, such as our model. Our numerical code makes it possible to discuss quantitatively the impact chemistry for various situations, such as the Galilean satellites. In this study, our numerical model is applied to the delivery of organic molecules via cometary impact on the Galilean satellites. Our numerical results indicate that small-particle impacts would produce HCN efficiently. Resulting HCN may freeze out immediately and be deposited on satellite surfaces, where it may be eventually converted into complex organics via irradiation of charged particle. On the other hand, large-size impacts may form transient CH4-N-2 atmospheres, in which complex organics (tholin) may be formed via energy deposition of UV and/or charged particle. Resulting complex organics may subsequently precipitate on the satellite surfaces without clear correlation with the locations of impact craters. Such distribution of complex organics created by chemical reactions within vapor plumes due to cometary impacts may explain an absorption (4.57 mu m) on Galilean satellites nonassociated with observable (moderate- and large-size) impact craters. (C) 2010 Elsevier Inc. All rights reserved.