Near-Surface Plasma Effects of OSIRIS-REx Sampling

Abstract:

Spacecraft are charged through their interaction with the solar wind plasma and via photoemission. Asteroids and other airless bodies have meter-scale plasma sheaths near their surfaces. During sampling, the electrically charged OSIRIS-REx spacecraft will come within 3m of the surface of Bennu, modifying the plasma environment near the asteroid’s surface. We will present models of the near-surface plasma environment considering an electrically floating spacecraft at a range of altitudes above Bennu. Since the Apollo era, it has been hypothesized that particles on the surface of airless bodies may detach due to electrostatic forces (called electrostatic lofting) [1,2]. While the presence of the OSIRIS-REx spacecraft during sampling may increase the surficial electric field strength by an order of magnitude to ~10-40 N/C, the surficial electric field strength will remain several orders of magnitude smaller than the inter-particle electric field (~10⁵ N/C [3]) that is likely to cause lofting. Additionally, the OSIRIS-REx sampling activity is likely to cause particle release (via mechanisms other than electrostatic lofting) outside of the sampler head. We will also evaluate the effect of electrostatic forces on the trajectories of particles detached from Bennu’s surface during sampling.

[1] Rennilson and Criswell (1974) “Surveyor Observations of the Lunar Horizon Glow”, The Moon, 10, 121-142.

[2] Lee (1996) “Dust Levitation on Asteroids” Icarus, 124, 181-194.

[3] Zimmerman et al (2016) “Grain-Scale Supercharging and Breakdown on Airless Regoliths” JGR:Planets, 121, 2016JE005049.