Analog Experiments for the Identification of Trace Biosignatures in Ice Grains from Extraterrestrial Ocean Worlds.
Analog Experiments for the Identification of Trace Biosignatures in Ice Grains from Extraterrestrial Ocean Worlds.
复制标题
DOI：
10.1089/ast.2019.2065
复制
发表时间：
2019-12
期刊：
影响因子：
4.2
通讯作者：
F. Klenner;F. Postberg;J. Hillier;N. Khawaja;R. Reviol;Ferdinand Stolz;M. Cable;B. Abel;L. Nölle
中科院分区：
文献类型：
--
作者：
F. Klenner;F. Postberg;J. Hillier;N. Khawaja;R. Reviol;Ferdinand Stolz;M. Cable;B. Abel;L. Nölle
可靠地识别外星海洋世界上的生物特征，如氨基酸、脂肪酸和肽，是寻找生命或在这些世界上出现的太空任务的关键先决条件。一种很有希望的方法是使用高性能的原位撞击电离质谱仪对来自欧罗巴或土卫二等海洋卫星的水冰粒进行取样。这种探测器的前身是卡西尼号航天器上的宇宙尘埃分析仪，它已经被证明在分析无机和有机海洋成分以及土卫二海洋的可居住性方面非常成功。然而，到目前为止，生物特征还没有在地外海洋环境中得到明确的识别。本文通过模拟实验研究了水冰粒中氨基酸、脂肪酸和多肽的光谱形态，以及它们在星载质谱仪上的检出限。我们采用了一种基于实验室的激光诱导液体束离子解吸技术，该技术被证明可以准确地模拟水冰粒在大范围撞击速度下的撞击电离质谱。所研究的有机物产生特征质谱，具有分子峰以及清晰可识别的独特片段。根据分子种类和仪器极性的不同，我们发现这些关键生物特征的检测限在μM或nM级别，并推断碰撞电离质谱仪在4-6 km/s的碰撞速度下对这些生物特征的分子峰最敏感。
Reliable identification of biosignatures, such as amino acids, fatty acids, and peptides, on extraterrestrial ocean worlds is a key prerequisite for space missions that search for life or its emergence on these worlds. One promising approach is the use of high-performance in situ impact ionization mass spectrometers to sample water ice grains emerging from ocean-bearing moons such as Europa or Enceladus. A predecessor of such detectors, the Cosmic Dust Analyzer on board the Cassini spacecraft, has proven to be very successful in analyzing inorganic and organic ocean constituents and with that characterizing the habitability of Enceladus ocean. However, biosignatures have not been definitively identified in extraterrestrial ocean environments so far. Here, we investigate with an analog experiment the spectral appearance of amino acids, fatty acids, and peptides in water ice grains, together with their detection limits, as applicable to spaceborne mass spectrometers. We employ a laboratory-based laser induced liquid beam ion desorption technique, proven to simulate accurately the impact ionization mass spectra of water ice grains over a wide range of impact speeds. The investigated organics produce characteristic mass spectra, with molecular peaks as well as clearly identifiable, distinctive fragments. We find the detection limits of these key biosignatures to be at the μM or nM level, depending on the molecular species and instrument polarity, and infer that impact ionization mass spectrometers are most sensitive to the molecular peaks of these biosignatures at encounter velocities of 4-6 km/s.