Isotopic composition of xenon and krypton in the lunar soil and in the solar wind

Abstract

Xe and Kr analyses of three lunar samples, the Murray meteorite and Xe from the terrestrial atmosphere are presented. The isotopic compositions of surface-correlated (solar wind?) and lunar soil spallation xenon and krypton are derived from the lunar soil data alone. The lunar soil spallation Xe is similar to that in lunar rocks and meteorites, but the lunar soil spallation Kr has higher (⁸⁴Kr/⁸³Kr) and ⁸²Kr/⁸³Kr). We have no adequate explanation for this Kr spectrum, although independent evidence for such a component comes from stepwise heating data. The surface-correlated Xe (SUCOR) is distinct from both AVCC and terrestrial Xe. However, SUCOR Xe cannot be directly identified with the solar wind, but may contain an admixture of gases from the lunar atmosphere implanted on the grain surfaces by ion pumping processes. The general fractionation trend in SUCOR Xe relative to the atmosphere presumably reflects the solar wind composition. SUCOR Kr appears to be totally ascribable to the solar wind. Solar wind and terrestrial Kr are related by fractionation, but opposite to that of Xe.