Physics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmsa21b..04y&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #SA21B-04
Physics
2427 Ionosphere/Atmosphere Interactions (0335), 5409 Atmospheres: Structure And Dynamics, 5707 Atmospheres: Structure And Dynamics, 5780 Tori And Exospheres
Scientific paper
We report on studies performed at the Laboratory for Surface Modification of Rutgers University and focused on the origin of alkali vapors (Na, K) in the tenuous atmospheres of the planet Mercury, the Moon, and Jupiter's icy satellite Europa [1, 2]; we also address the question why alkaline-earth metals (Mg, Ca) are less abundant in the atmospheres. A variety of ultrahigh-vacuum surface science techniques are used, including X-ray Photoelectron Spectroscopy (XPS), Low-Energy Ion Scattering (LEIS), Thermal Programmed Desorption (TPD), Electron- and Photon-Stimulated Desorption (ESD and PSD), Surface Ionization (SI). Measurements have been made on different samples, including the model mineral binary oxide SiO2 that simulates lunar silicates, and a lunar sample obtained from NASA. Desorption induced by electronic excitations (mainly PSD) rather than by thermal processes is found to be the dominant source process on the lunar surface. The flux at the lunar surface of ultraviolet photons from the Sun is adequate to insure that PSD of sodium contributes substantially to the Moon's atmosphere. A model based on irradiation-induced charge-transfer is proposed to explain the desorption process. There is a strong temperature-dependence of Na ESD and PSD signals from a lunar sample, under conditions where the Na surface coverage is constant and thermal desorption is negligible [3]. On Mercury solar heating of the surface is high enough that thermal desorption will also be a potential source of atmospheric sodium. Ion bombardment of the lunar sample causes both the sputtering of alkali atoms into vacuum and implantation into the sample bulk. In the future we outline the use a novel method, Nuclear Resonance Profiling (NRP) to study the diffusion of alkalis through model minerals, ices, and lunar samples; these measurements would provide additional information to understand the replenishment of Na at the surface of the Moon, Mercury and Europa. We also describe a new detector that we will use to search for desorption of alkaline-earth atoms. [1] T.E. Madey, R.E. Johnson, T.M. Orlando, Surf. Sci. 500 (2002) 838. [2] B.V. Yakshinskiy, T.E. Madey, Surf. Sci. 528 (2003) 54. [3] B.V. Yakshinskiy, T.E. Madey, Icarus 168 (2004) 53.
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