In-Situ Measurements Of Electrostatically Lofted Dust On The Lunar Surface
One of the great science questions about the Moon, and other airless bodies, is to understand the role of electrostatic dust transport in shaping the properties of their surfaces. This process has been hypothesized to explain a number of unusual planetary phenomena. The first evidence was the so-called lunar horizon glow. The high-altitude ray-pattern streamers above the lunar surface reported by the Apollo astronauts and the low-speed dust impact events registered in the LEAM instrument are additional lunar observations indicating the possible existence of electrostatically lofted dust. Since then, several observations from other airless bodies, such as the radial spokes in Saturn’s rings and the “dust ponds” on asteroid Eros and comet 67P, have also been related to this electrostatic dust transport process. The exact mechanism of the transport and lofting of charged dust particles, however, remained unsolved for decades. Recent laboratory studies have greatly advanced the understanding of this process (Wang et al., 2016; Schwan et al., 2017). Micron-sized dust particles were lofted to several cm high on Earth by exposure to UV or plasmas. A new “patched charge model” developed and validated with the experiments explains that the emission and re-absorption of photo and/or secondary electrons inside microcavities formed between neighboring dust particles can result in surprisingly large negative charges on these dust particles. The resulting repulsive force between them ejects the dust particles off the surface. These experiments also showed that electrostatic dust mobilization/transport can be an efficient process in shaping the surfaces of airless bodies, providing a new paradigm for their formation and evolution. In-situ measurements are needed to verify and characterize this process in order to better estimate its effect on the regolith physical properties and near-surface dust environment around airless bodies. In addition, these measurements will provide insight into potential dust hazards and enable the development of mitigation strategies for future robotic and/or human exploration. A new dust instrument for detecting and measuring low-speed electrostatically lofted dust particles is under development at the University of Colorado. This paper will briefly discuss the instrument design and measurement requirements. The preferred landing site would be the areas exposed to sunlight (lower latitudes) because photoemission is expected to be an efficient charging process for dust lofting on the lunar surface (Wang et al., 2016). Mobility and sample return are not needed for these measurements. -------------- Wang, X., J. Schwan, H.-W. Hsu, E. Grün, and M. Horányi (2016), Dust charging and transport on airless planetary bodies, Geophys. Res. Lett., 43, 6103–6110, doi:10.1002/2016GL069491. Schwan, J., X. Wang, H.-W. Hsu, E. Grün, and M. Horányi (2017), The charge state of electrostatically transported dust on regolith surfaces, Geophys. Res. Lett., 44, 3059–3065, doi:10.1002/2017GL072909.