DPS 2001 meeting, November 2001
Session 62. Laboratory Studies
Oral, Chairs: R. Wu, R. Hudson, Saturday, December 1, 2001, 4:40-5:50pm, Regency GH

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[62.01] Generation of Na atmospheres by Sputtering and Thermal Desorption

C.A. Dukes, R.A. Baragiola (University of Virginia)

Sodium has been detected in the atmosphere surrounding many bodies within our solar system. In particular, Mercury, the Moon, and Io exhibit significant concentrations of atomic sodium in their exospheres. In addition, recent observations suggest that Na also appears in the atmosphere surrounding asteroids. Thermal desorption, photon-stimulated desorption, electron-stimulated desorption, ion bombardment, and micro meteoritic impact have all been suggested as mechanisms for Na ejection from planetary surfaces into their atmospheres.

We investigate two of these processes: ion bombardment and thermal desorption. The effect of solar wind bombardment is studied by irradiating labradorite (a plagioclase feldspar similar to that of lunar basalt) with 4 keV He ions and measuring the surface concentration of Na as a function of dose with x-ray photoelectron spectroscopy (XPS). The amount of Na that thermally desorbs, particularly important for Mercury, is determined by heating labradorite and measuring *in situ* the chemical composition of the mineral surface as a function of temperature. We will discuss the astronomical implications of our measurements.

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