The dayside near-surface lunar plasma environment is electrostatically complex, due to the interaction between solar UV-induced photoemission, the collection of ambient ions and electrons, and the presence of micron and sub-micron sized dust grains.

Further complicating this environment, although less well understood in effect, is the presence of surface relief, typically in the form of craters and/or boulders.

It has been suggested that such non-trivial surface topography can lead to complex electrostatic potentials and fields, including “mini-wakes” behind small obstacles to the solar wind flow and “supercharging” near sunlit-shadowed boundaries.

A team of NLSI scientists, lead by Andrew Poppe at the University of California, modeled the dayside near-surface lunar plasma environment over a variety of local times with the presence of a crater and presented results in a paper titled “The effect of surface topography on the lunar photoelectron sheath and electrostatic dust transport” published in the August issue of the journal Icarus. This is yet another excellent example of continued collaboration between NLSI’s DREAM and CCLDAS teams.

Additionally, the scientists used the particle-in-cell model output to study the effect of surface topography on the dynamics of electrostatic dust transport, with the goal of understanding previous observations of dust dynamics on the Moon and dust ponding on various asteroids.

Their results confirm earlier models of electrostatic dust transport near lunar and/or asteroidal craters, while extending our understanding of how surface relief, via the presence of complex electrostatic fields, affects both the individual and bulk transport of dust grains.

The significant lack of knowledge about dust grain launching mechanisms, including the launching probability as a function of grain size and plasma conditions, and the distribution of initial velocities prevents scientists from establishing absolute rates on dust transport into craters.

A full understanding of the mechanics and subsequent dynamics of dust grains in electrostatically complex environments such as the surface of the Moon requires in-situ measurements in order to constrain the size, velocity, and charge of electrostatically transported grains.

The presence of boulders near or within a crater should be further studied, as these objects tend to break the symmetry of the crater and may introduce complex patterns in both the plasma environment and electrostatic dust transport. Many of the geometries that could be simulated with lunar topography may also apply to the construction and emplacement of man-made structures.

A full understanding of the plasma and electric field environment near such structures will be critical for successfully operating and living in the lunar environment. Further laboratory and in-situ investigations are required to understand electrostatic launching and transport of lunar and asteroidal dust grains.

Posted by: Soderman/NLSI Staff
Source: NLSI Team/ http://www.sciencedirect.com/science/article/pii/S0019103512002941

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