Detection of spark discharges in an agitated Mars dust simulant isolated from foreign surfaces. (arXiv:2006.01978v3 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Harper_J/0/1/0/all/0/1">Joshua Méndez Harper</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dufek_J/0/1/0/all/0/1">Josef Dufek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McDonald_G/0/1/0/all/0/1">George McDonald</a>
Numerous laboratory experiments, starting in the Viking Lander era, have
reported that frictional interactions between Martian analog dust grains can
catalyze electrostatic processes (i.e. triboelectrification). Such findings
have been cited to suggest that Martian dust devils and dust storms may sustain
lightning storms, glow discharges, and other complex electrostatic phenomena.
However, in many cases (if not most), these experiments allowed Martian dust
simulant grains to contact foreign surfaces (for instance, the wall of an
environmental chamber or other chemically dissimilar particles). A number of
authors have noted that such interactions could produce charging that is not
representative of processes occurring near the surface of Mars. In this work,
we experimentally characterize the triboelectrification of a Martian dust
simulant resulting from both isolated particle-particle collisions and
particle-wall collisions under a simulated Martian environment. For the first
time, we report the direct detection of spark discharges under Martian surface
conditions in a flow composed solely of natural basalt and isolated from
man-made surfaces. The charge densities acquired by the fluidized grains are
found to be of order 10^-6 Cm^-2 (in excess of the theoretical maximum charge
density for the near-surface Martian environment). Additionally, we demonstrate
that the interaction of simulant particles with experimental walls can modulate
the polarity of spark discharges. Our work supports the idea that small-scale
spark discharges may indeed be present in Martian granular flows and may be
qualitatively similar to small-scale discharges in terrestrial volcanic vents.
Numerous laboratory experiments, starting in the Viking Lander era, have
reported that frictional interactions between Martian analog dust grains can
catalyze electrostatic processes (i.e. triboelectrification). Such findings
have been cited to suggest that Martian dust devils and dust storms may sustain
lightning storms, glow discharges, and other complex electrostatic phenomena.
However, in many cases (if not most), these experiments allowed Martian dust
simulant grains to contact foreign surfaces (for instance, the wall of an
environmental chamber or other chemically dissimilar particles). A number of
authors have noted that such interactions could produce charging that is not
representative of processes occurring near the surface of Mars. In this work,
we experimentally characterize the triboelectrification of a Martian dust
simulant resulting from both isolated particle-particle collisions and
particle-wall collisions under a simulated Martian environment. For the first
time, we report the direct detection of spark discharges under Martian surface
conditions in a flow composed solely of natural basalt and isolated from
man-made surfaces. The charge densities acquired by the fluidized grains are
found to be of order 10^-6 Cm^-2 (in excess of the theoretical maximum charge
density for the near-surface Martian environment). Additionally, we demonstrate
that the interaction of simulant particles with experimental walls can modulate
the polarity of spark discharges. Our work supports the idea that small-scale
spark discharges may indeed be present in Martian granular flows and may be
qualitatively similar to small-scale discharges in terrestrial volcanic vents.
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