Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p31b1397m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P31B-1397
Physics
2129 Interplanetary Dust, 2164 Solar Wind Plasma, 2194 Instruments And Techniques, 6213 Dust, 6250 Moon (1221)
Scientific paper
The tenuous lunar atmosphere is a surface-bound exosphere (SBE) similar to that found throughout the solar system, for example on Mercury, various icy satellites, over the rings of Saturn, on large asteroids, and on Kuiper Belt objects. Its time-dependent constituents arise from a dynamic balance between sources that may be sporadic (solar wind, sputtering, micrometeoroid impacts, outgassing) and loss mechanisms (escape, ionization). In an SBE, the atoms and molecules released from the surface follow approximately ballistic orbits, either returning to the surface or escaping to space without collisions. The mechanisms by which the lunar atmosphere is formed, in particular the role of constant micrometeoroid bombardment of the lunar surface, are subject to ongoing debate. We discuss here a series of open questions regarding the lunar atmosphere as well as an experimental program to address them. Particular outstanding questions include: What is the relative role of hypervelocity micrometeoroid impacts vs. Solar wind sputtering in regolith escape? Similarly, what is their relative role in the production of the observed Na in the exosphere? What is the physical mechanism by which He is released from the regolith, and under what conditions is it released with sub-escape velocities? How is implanted He freed preferentially to 40Ar? How do the particulate ejecta and plasma clouds released from micrometeoroid impacts interact, and how do they affect the lofting of fine regolith material? Laboratory investigation of these basic physical mechanisms can additionally provide input to the analysis and interpretation of the forthcoming LADEE measurements. The necessary experimental program considerations include appropriate sources, including a hypervelocity dust accelerator with the ability to accelerate micron-sized dust particles to realistic velocities (tens of km/s), and the capability for sputtering by solar wind constituent ions at realistic energies (~1 keV). Diagnostic considerations include the ability to measure the energy distribution, angular distribution, and composition of both vapor and particulate debris removed by both sputtering and micrometeoroid impact into realistic regolith material. In this talk, we describe the scientific and technical details of such an experimental program, including the specifics of how many outstanding questions can be directly addressed.
Gruen Eberhard
Hodges Richard R.
Horanyi Mihaly
Munsat T.
Robertson Scott
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