Dust is a dominant feature of the surface, atmosphere, and climate of Mars. It poses a potential hazard to astronauts and equipment, and is therefore important to take into account when preparing for future missions to Mars, specifically crewed missions. Despite its importance, little is known about the size and charge of Martian dust because these parameters have only been measured indirectly. In order to understand these physical parameters, our research focuses on developing an instrument based on charge-detection mass spectrometry (CD-MS) to directly measure the mass, which can be related to size, and charge of individual dust particles. At the core of our CD-MS instrument is a linear charge detector. The detector is roughly the size of a smartphone and consists of a series of copper electrodes patterned onto two printed circuit boards (PCBs). The PCBs are sandwiched together and spaced about 5 mm apart, allowing particles to pass between them. As a particle passes each electrode pair, it generates a charge signal. This signal is amplified by a charge amplifier and measures charge, kinetic energy, and velocity. A second velocity measurement is attained by applying a DC voltage to the central electrode, which accelerates or decelerates the particles depending on charge polarity. Particle mass is then calculated from these measurements.<br/>In initial development, electrosprayed polystyrene spheres which have approximately the same size and charge as expected for Mars dust (~1-5 µm in diameter, ~5-10,000 charges) were analyzed to ensure that the detector can accurately measure the desired parameters. Future experiments will analyze electrosprayed regolith simulant composed of olivine and other minerals that closely resembles Martian dust.<br/>Data analysis from this linear charge detector is performed in the time domain, and particle velocity is measured across each electrode. We have shown that velocities across electrodes of the PCB detector agree with each other within 0.44% RSD. This velocity agreement, in combination with a &gt;10% velocity change across the central DC electrode, yields more accurate mass determination. Results from our initial development of our CD-MS instrument will be presented.

Characterization of Martian atmospheric dust using charge detection mass spectrometry (CD-MS)

ACS Spring 2022

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