Icy moons like Enceladus, and perhaps Europa, emit material sourced from their subsurface oceans into space via plumes of ice grains and gas. Both moons are prime targets for astrobiology investigations. Cassini measurements revealed a large compositional diversity of emitted ice grains with only 1 to 4% of Enceladus’s plume ice grains containing organic material in high concentrations. Here, we report experiments simulating mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by advanced instruments on board future space missions to Enceladus or Europa, such as the SUrface Dust Analyzer onboard NASA’s upcoming Europa Clipper mission at flyby speeds of 4 to 6 kilometers per second. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future missions, even if an ice grain contains much less than one cell. Our results demonstrate the advantage of analyses of individual ice grains compared to a diluted bulk sample in a heterogeneous plume.

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如何识别土卫二或木卫二发出的单个冰粒中的细胞物质

像土卫二这样的冰冷卫星，也许还有木卫二，通过冰粒和气体羽流将来自地下海洋的物质排放到太空中。这两颗卫星都是天体生物学研究的主要目标。卡西尼号测量结果显示，所喷出的冰粒成分存在很大差异，土卫二羽状冰粒中只有 1% 到 4% 含有高浓度的有机物质。在这里，我们报告了模拟含有一种细菌细胞或其部分的冰粒质谱的实验，这些冰粒是未来土卫二或欧罗巴太空任务中的先进仪器所遇到的，例如美国宇航局即将进行的欧罗巴快艇任务中以飞越速度运行的表面灰尘分析仪每秒4至6公里。即使冰粒中含有的细胞远少于一个，细菌的质谱信号特征也可以通过未来的任务清楚地识别出来。我们的结果证明了与异质羽流中稀释的散装样品相比，对单个冰粒进行分析的优势。