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The lunar exosphere: The sputtering contribution |
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| Authors: | P Wurz U Rohner JA Whitby H Lammer JA Martín-Fernández |
| Institution: | a Physikalisches Institut, Universität Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland b Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria c Institute for Physics, University of Graz, Universitätsplatz 5/II, A-8010 Graz, Austria d Department for Computer Science and Applied Mathematics, University of Girona, Edifici, P-IV, Campus Montilivi, E-17071 Girona, Spain |
| Abstract: | We have extended our Monte Carlo model of exospheres Wurz, P., Lammer, H., 2003. Icarus 164 (1), 1-13] by treating the ion-induced sputtering process from a known surface in a self-consistent way. The comparison of the calculated exospheric densities with experimental data, which are mostly upper limits, shows that all of our calculated densities are within the measurement limits. The total calculated exospheric density at the lunar surface of about 1×107 m−3 as result of solar wind sputtering we find is much less than the experimental total exospheric density of about 1012 m−3. We conclude that sputtering contributes only a small fraction of the total exosphere, at least close to the surface. Because of the considerably larger scale height of atoms released via sputtering into the exosphere, sputtered atoms start to dominate the exosphere at altitudes exceeding a few 1000 km, with the exception of some light and abundant species released thermally, e.g. H2, He, CH4, and OH. Furthermore, for more refractory species such as calcium, our model indicates that sputtering may well be the dominant mechanism responsible for the lunar atmospheric inventory, but observational data does not yet allow firm conclusions to be drawn. |
| Keywords: | Moon Moon surface Atmospheres composition |
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