Belousov Anton, Miller Morgan, Continetti Robert, Madzunkov Stojan, Simcic Jurij, Nikolic Dragan, Maiwald Frank, Waller Sarah, Malaska Michael, Cable Morgan
NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, United States.
University of California San Diego, Mail Code 0340, 9500 Gilman Drive, La Jolla, California 92093-0340, United States.
J Am Soc Mass Spectrom. 2021 Apr 1. doi: 10.1021/jasms.0c00442.
The Enceladus plume is a target of astrobiological interest in planetary science since it may carry signs of extraterrestrial life entrapped in ice grains formed from the subsurface ocean of this moon of Saturn. Fly-by mission concepts have been proposed to perform close investigations of the plume, including detailed in situ measurements of chemical composition with a new generation of mass spectrometer instrumentation. Such a scenario involves high-velocity collisions (typically around 5 km/s or higher) of the instrument with the encountered ice grains. Postimpact processes may include molecular fragmentation, impact ionization, and various subsequent chemical reactions that could alter the original material prior to analysis. In order to simulate Enceladus plume fly through conditions, we are developing an ice grain accelerator and have coupled it to the quadrupole ion trap mass spectrometer (QITMS) developed for flight applications. Our experimental setup enables the creation and acceleration of ice particles with well-defined size, charge, and velocity, which are subsequently directed into the QITMS, where they impact the surface of the mass analyzer and the analysis of postimpact, volatilized molecules takes place. In this work, we performed mass spectral analysis of ice grains of ca. 1.3 μm in diameter, accelerated and impacted at velocities up to 1000 m/s, with an upgrade of the accelerator in progress that will enable velocities up to 5000 m/s. We report the first observations of ice grain impacts measured by the QITMS, which were recorded as brief increases in the abundance of water molecules detected within the instrument.
土卫二羽流是行星科学中天体生物学感兴趣的目标，因为它可能携带来自这颗土星卫星地下海洋形成的冰粒中所捕获的外星生命迹象。已经提出了飞越任务概念，以对羽流进行近距离研究，包括使用新一代质谱仪仪器对化学成分进行详细的原位测量。这种情况涉及仪器与所遇到的冰粒的高速碰撞（通常约为5千米/秒或更高）。撞击后的过程可能包括分子破碎、撞击电离以及各种后续化学反应，这些反应可能在分析之前改变原始物质。为了模拟飞越土卫二羽流的条件，我们正在开发一种冰粒加速器，并将其与为飞行应用开发的四极离子阱质谱仪（QITMS）耦合。我们的实验装置能够产生并加速具有明确尺寸、电荷和速度的冰粒子，随后将它们导入QITMS，在那里它们撞击质量分析器的表面，并对撞击后挥发的分子进行分析。在这项工作中，我们对直径约1.3微米的冰粒进行了质谱分析，这些冰粒以高达1000米/秒的速度加速并撞击，同时正在对加速器进行升级，升级后将能够实现高达5000米/秒的速度。我们报告了QITMS测量到的冰粒撞击的首次观测结果，这些结果被记录为仪器内检测到的水分子丰度的短暂增加。
