Ejecta charging and dynamics in meteoroid impacts on asteroids and comets

Abstract:

Hypervelocity impacts produce a dense plume of partially ionized gas and condensed phase debris. As the plume expands out from the impact crater, plasma oscillations and instabilities lead to electromagnetic emissions. Ejected particles interact with the plasma and acquire a surface charge, potentially leading to macroscopic charge separation and long-range fields. Bodies in space, including spacecraft, asteroids, comets, and airless moons, routinely experience such impacts by the meteoroid and dust population, and spacecraft in Earth orbit face the additional threat of collision with space debris. The impact-generated plasma and associated emissions pose a threat to spacecraft electronics, but in-situ analysis of impact products may provide valuable data about the nature of small solar system bodies and the space environment.

In a 2019 light gas gun impact campaign at NASA Ames Vertical Gun Range, we measured the size and shape distributions of microscopic debris from impacts on aluminum and powdered regolith simulant targets. Applying dust charging and dynamics models to the measured ejecta distributions suggests significant charge attachment is possible, especially shortly after impact, and under certain conditions, dust may become positively charged. High speed camera observations show plasma being ``dragged'' along the ejecta curtain, and plasma measurements from Faraday cup sensors show evidence of both positively and negatively charged dust. We present estimates of dust charging under a range of conditions characteristic of the post-impact environment for both spacecraft and small solar system bodies. We also investigate how facility effects, such as partial vacuum, influence results obtained from ground-based experiments, and whether such conditions may serve as analogues for the environment around outgassing comets. Finally, we consider the potential to characterize asteroids and comets using measurements of the dusty plasma produced by naturally occurring impacts.