Enceladus is a compelling destination for astrobiological analyses due to the presence of simple and complex organic constituents in cryovolcanic plumes that jet from its subsurface ocean. Enceladus plume capture during a flyby or orbiter mission is an appealing method for obtaining pristine ocean samples for scientific studies of this organic content because of the high science return, reduced planetary protection challenges, and lower risk and expense compared to a landed mission. However, this mission profile requires sufficient amounts of plume material for sensitive analysis. To explore the feasibility and optimization of the required capture systems, light gas gun experiments were carried out to study organic ice particle impacts on indium surfaces. An organic fluorescent tracer dye, Pacific Blue™, was dissolved in borate buffer and frozen into saline ice projectiles. During acceleration, the ice projectile breaks up in flight into micron‐sized particles that impact the target. Quantitative fluorescence microscopic analysis of the targets demonstrated that under certain impact conditions, 10–50% of the entrained organic molecules were captured in over 25% of the particle impacts. Optimal organic capture was observed for small particles (d ~ 5–15 µm) with velocities ranging from 1 to 2 km s\(^{−1}\). Our results reveal how organic capture efficiency depends on impact velocity and particle size; capture increases as particles get smaller and as velocity is reduced. These results demonstrate the feasibility of collecting unmodified organic molecules from the Enceladus ice plume for sensitive analysis with modern in situ instrumentation such as microfluidic capillary electrophoresis (CE) analysis with ppb organic sensitivity.

中文翻译：

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土卫二羽流生物特征分析的可行性：在超高速撞击中成功捕获有机冰粒

由于从地下海洋喷出的冰火山羽流中存在简单和复杂的有机成分，土卫二是天体生物学分析的一个引人注目的目的地。在飞越或轨道飞行器任务期间捕获土卫二羽流是获取原始海洋样本用于对这种有机成分进行科学研究的一种有吸引力的方法，因为与着陆任务相比，科学回报高、行星保护挑战减少以及风险和费用较低。然而，这个任务剖面需要足够数量的羽流物质来进行敏感分析。为了探索所需捕获系统的可行性和优化，进行了轻气枪实验以研究有机冰粒子对铟表面的影响。一种有机荧光示踪染料 Pacific Blue™，将其溶解在硼酸盐缓冲液中并冷冻成盐水冰弹。在加速过程中，冰弹在飞行中分裂成微米大小的粒子，撞击目标。目标的定量荧光显微分析表明，在某些撞击条件下，10-50% 的夹带有机分子在超过 25% 的粒子撞击中被捕获。对于速度范围为 1 至 2 km s\(^{−1}\) 的小颗粒 (d ~ 5–15 µm)，观察到最佳有机捕获。我们的结果揭示了有机物捕获效率如何取决于撞击速度和颗粒大小；随着粒子变小和速度降低，捕获增加。