Overview

We study the fundamental physics that dictate the behavior of grains on planetary surfaces and the subsequent dynamics of the grains. We are especially interested in the influence of non-gravitational forces on grain dynamics, specifically cohesion and electrostatic forces. We seek to understand the morphological evolution of planetary surfaces (specifically asteroids and the Moon) as well as improve the design of spacecraft to explore these destinations.

Electrostatic Dust Lofting

Electrostatic dust motion has been hypothesized to occur on the Moon and asteroids. Airless bodies (i.e. those bodies with negligible or minimal atmospheres) interact directly with the solar wind plasma. Under certain conditions, the electrostatic force on dust grains may be stronger than the gravitational and cohesive forces holding grains against the surface, leading to dust lofting. We seek to answer questions associated with understanding the feasibility and implications of dust lofting: What size dust can be lofted? What plasma environment is required for lofting to occur? We have analytically and experimentally demonstrated the significance of cohesion in evaluating the feasibility of electrostatic lofting of small grains.

Electrostatic Dust Levitation

If dust grains are launched off the surface of a small body within a narrow range of initial velocities, the grains can levitate due to the opposition of the gravitational and electrostatic forces. We study the dynamics of lofting dust grains to determine what range of initial velocities lead to levitation, the locations where levitating grains may be observed, and the locations where grains are redeposited. Through our studies of levitation in 1D plasma sheaths and gravity models, we have shown that grains up to 3 microns radius are capable of stable levitation above the asteroid Itokawa and that the size of levitating grain decreases as the mass of the central body increases. Additionally, we have shown that the range of launching velocities that leads to levitation is more dependent on grain size than central body mass.

Granular Flows

We are interested in understanding the physics of granular flows in low gravity environments, specifically avalanching on low-gravity bodies like asteroids and the Moon. In order to study granular flows in this type of environment, we are developing a Contact Dynamics (CD) simulation. CD simulations are similar to Discrete Element Method simulations where there is a constant timestep and the interactions of grains are controlled through coefficients of friction and restitution. We intend to use this type of simulation to also aid in the design of future spacecraft sample collection, anchoring and mobility devices.