The atomic-scale fragmentation processes involved in molecules undergoing hypervelocity impacts (HVIs; defined as >3 km/s) are challenging to investigate via experiments and still not well understood. This is particularly relevant for the consistency of biosignals from small-molecular-weight neutral organic molecules obtained during solar system robotic missions sampling atmospheres and plumes at hypervelocities. Experimental measurements to replicate HVI effects on neutral molecules are challenging, both in terms of accelerating uncharged species and isolating the multiple transition states over very rapid timescales (<1 ps). Nonequilibrium first-principles-based simulations extend the range of what is possible with experiments. We report on high-fidelity simulations of the fragmentation of small organic biosignature molecules over the range v = 1−12 km/s, and demonstrate that the fragmentation fraction is a sensitive function of velocity, impact angle, molecular structure, impact surface material, and the presence of surrounding ice shells. Furthermore, we generate interpretable fragmentation pathways and spectra for velocity values above the fragmentation thresholds and reveal how organic molecules encased in ice grains, as would likely be the case for those in “ocean worlds,” are preserved at even higher velocities than bare molecules. Our results place ideal spacecraft encounter velocities between 3 and 5 km/s for bare amino and fatty acids and within 4–6 km/s for the same species encased in ice grains and predict the onset of organic fragmentation in ice grains at >5 km/s, both consistent with recent experiments exploring HVI effects using impact-induced ionization and analysis via mass spectrometry and from the analysis of Enceladus organics in Cassini Data. From nanometer-sized ice Ih clusters, we establish that HVI energy is dissipated by ice casings through thermal resistance to the impact shock wave and that an upper fragmentation velocity limit exists at which ultimately any organic contents will be cleaved by the surrounding ice—this provides a fundamental path to characterize micrometer-sized ice grains. Altogether, these results provide quantifiable insights to bracket future instrument design and mission parameters.

中文翻译：

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了解太空任务中生物特征的超高速采样

经历超高速撞击（HVI；定义为> 3 km/s）的分子所涉及的原子级碎裂过程很难通过实验进行研究，而且仍然没有得到很好的理解。这对于在太阳系机器人任务以超高速采样大气和羽流期间获得的小分子量中性有机分子的生物信号的一致性特别相关。复制 HVI 对中性分子影响的实验测量具有挑战性，无论是在加速不带电物质还是在非常快的时间尺度（< 1 ps）内隔离多个过渡态方面。基于非平衡第一原理的模拟扩展了实验的可能性范围。我们报告了在v  = 1 − 12 km/s范围内有机生物特征分子碎片的高保真模拟，并证明碎片分数是速度、撞击角度、分子结构、撞击表面材料的敏感函数，以及周围冰壳的存在。此外，我们针对高于破碎阈值的速度值生成可解释的破碎路径和光谱，并揭示了包裹在冰粒中的有机分子（就像“海洋世界”中的有机分子的情况一样）如何以比裸露分子更高的速度保存。我们的结果表明，对于裸露的氨基酸和脂肪酸，理想的航天器遇到速度在 3 至 5 公里/秒之间，对于包裹在冰粒中的同一物种，理想的航天器遇到速度在 4-6 公里/秒内，并预测冰粒中有机碎片在> 5 公里处开始/s，两者都与最近使用撞击诱导电离和质谱分析探索 HVI 效应的实验以及卡西尼数据中土卫二有机物的分析一致。从纳米尺寸的冰 Ih 簇中，我们确定 HVI 能量通过冰壳对冲击冲击波的热阻而消散，并且存在一个破碎速度上限，在该速度下，任何有机成分最终都会被周围的冰裂解——这提供了表征微米尺寸冰粒的基本途径。总而言之，这些结果为未来的仪器设计和任务参数提供了可量化的见解。