Space Sciences Laboratory, University of California, Berkeley, CA 94720.
School of Physical Sciences, University of Kent, Kent CT2 7NH, United Kingdom.
Proc Natl Acad Sci U S A. 2021 Sep 14;118(37). doi: 10.1073/pnas.2106197118.
Enceladus, an icy moon of Saturn, is a compelling destination for a probe seeking biosignatures of extraterrestrial life because its subsurface ocean exhibits significant organic chemistry that is directly accessible by sampling cryovolcanic plumes. State-of-the-art organic chemical analysis instruments can perform valuable science measurements at Enceladus provided they receive sufficient plume material in a fly-by or orbiter plume transit. To explore the feasibility of plume sampling, we performed light gas gun experiments impacting micrometer-sized ice particles containing a fluorescent dye biosignature simulant into a variety of soft metal capture surfaces at velocities from 800 m ⋅ s up to 3 km ⋅ s Quantitative fluorescence microscopy of the capture surfaces demonstrates organic capture efficiencies of up to 80 to 90% for isolated impact craters and of at least 17% on average on indium and aluminum capture surfaces at velocities up to 2.2 km ⋅ s Our results reveal the relationships between impact velocity, particle size, capture surface, and capture efficiency for a variety of possible plume transit scenarios. Combined with sensitive microfluidic chemical analysis instruments, we predict that our capture system can be used to detect organic molecules in Enceladus plume ice at the 1 nM level-a sensitivity thought to be meaningful and informative for probing habitability and biosignatures.
土卫二，土星的一颗冰冷卫星，是探索外星生命生物特征的一个极具吸引力的目标，因为其地下海洋中存在大量有机化合物，可通过对冰火山羽流进行采样直接获取。只要在飞掠或轨道器羽流飞越过程中能获得足够的羽流物质，最先进的有机化学分析仪器就能在土卫二上进行有价值的科学测量。为了探索羽流采样的可行性，我们使用轻气枪实验，将含有荧光染料生物特征模拟物的微米级冰颗粒以 800 m ⋅ s 至 3 km ⋅ s 的速度撞击到各种软金属捕获表面上。对捕获表面进行定量荧光显微镜分析表明，对于孤立的撞击坑，有机捕获效率高达 80%至 90%，对于铟和铝捕获表面，在高达 2.2 km ⋅ s 的速度下，平均捕获效率至少为 17%。我们的结果揭示了在各种可能的羽流飞越场景中，撞击速度、颗粒大小、捕获表面和捕获效率之间的关系。结合高灵敏度的微流控化学分析仪器，我们预测我们的捕获系统可用于检测土卫二羽流冰中的有机分子，检测灵敏度可达 1 nM 水平——这一灵敏度被认为对探测宜居性和生物特征具有重要意义和信息价值。
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