Predictions for Electrostatic Dust Levitation about Bennu’s Equator

Abstract:

Electrostatic dust levitation was first hypothesized to occur on the Moon due to observations of Lunar Horizon Glow and results from the Apollo 17 LEAM instrument. Due to their weaker gravitational acceleration and similar plasma environment, electrostatic dust motion was also hypothesized to occur on asteroids. There is still no conclusive evidence, however, that electrostatic levitation occurs on either asteroids or the Moon. The OSIRIS-REx mission will visit the asteroid Bennu in 2018-2019. We have numerically modeled the plasma environment around the equator of Bennu, with the asteroid assumed to have a circular equatorial cross section. Our plasma model presents a significant improvement over previous semi-analytical models as it can seamlessly capture the transition from day-side plasma sheath to night-side plasma wake. Using the plasma model and assuming a uniform density for gravity calculations, we identify the altitudes, longitudinal locations, and the associated grain sizes at which electrostatic levitation is expected to occur. Our predictions of dust levitation at Bennu will enable assessments of the observability of levitating dust during the OSIRIS-REx mission and guide any observations.