Electrostatic forces on grains near asteroids and comets

Christine Hartzell,Dylan Carter

doi:10.1051/epjconf/201714014009

Abstract

Dust on and near the surface of small planetary bodies (e.g. asteroids, the Moon, Mars’ moons) is subject to gravity, cohesion and electrostatic forces. Due to the very low gravity on small bodies, the behavior of small dust grains is driven by non-gravitational forces. Recent work by Scheeres et al. has shown that cohesion, specifically van der Waals force, is significant for grains on asteroids. In addition to van der Waals cohesion, dust grains also experience electrostatic forces, arising from their interaction with each other (through tribocharging) and the solar wind plasma (which produces both grain charging and an external electric field). Electrostatic forces influence both the interactions of grains on the surface of small bodies as well as the dynamics of grains in the plasma sheath above the surface. While tribocharging between identical dielectric grains remains poorly understood, we have recently expanded an existing charge transfer model to consider continuous size distributions of grains and are planning an experiment to test the charge predictions produced. Additionally, we will present predictions of the size of dust grains that are capable of detaching from the surface of small bodies.

Highlights

Small planetary bodies, such as asteroids and comets, have increasingly become attractive targets for space exploration missions because of their scientific value, potential hazard to Earth, and as a possible human exploration destination
In addition to grain charging due to interactions of the surface of an airless body with the solar wind plasma, grains may charge during spacecraft activities via tribocharging; the exchange of charge when grains collide or slide against one another
While it is known that tribocharging between dielectric grains of the same material occurs, there is currently no prevailing theory of the physical underpinnings of this charge exchange [10]

Summary

Introduction

Small planetary bodies, such as asteroids and comets, have increasingly become attractive targets for space exploration missions because of their scientific value, potential hazard to Earth, and as a possible human exploration destination (as an intermediate step before Mars). In addition to grain charging due to interactions of the surface of an airless body with the solar wind plasma, grains may charge during spacecraft activities via tribocharging; the exchange of charge when grains collide or slide against one another. The leading theory of same-material dielectric tribocharging is that the charge exchange is due to electrons transitioning from high energy states on one grain to low energy states on the second grain [11]. Given this physical mechanism of charge exchange, it is possible to create semi-analytical predictions of the level of charging in a mixture of grains. By improving our understanding of the dielectric samematerial charging, we will be able to predict the level of grain charging induced by spacecraft activity and the subsequent interaction of grains with the local plasma environment

Grain Lofting

Tribocharging of Dielectric Same-Material Grains

Conclusion