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Synodic and semiannual oscillations of argon‐40 in the lunar exosphere

2015; American Geophysical Union; Volume: 43; Issue: 1 Linguagem: Inglês

10.1002/2015gl067293

1944-8007

R. R. Hodges, P. R. Mahaffy,

Space Science and Extraterrestrial Life

Abstract The neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft collected a trove of exospheric data, including a set of high‐quality measurements of radiogenic 40 Ar over a period of 142 days. Data synthesis studies, using well‐established exosphere simulation tools, show that the LADEE argon data are consistent with an exosphere‐regolith interaction that is dominated by adsorption and that the desorption process generates the Armand distribution of exit velocities. The synthesis work has uncovered an apparent semiannual oscillation of argon that is consistent with temporal sequestration in the seasonal cold traps created at the poles by the obliquity of the Moon. In addition, the LADEE data provide new insight into the pristine nature of lunar regolith, its spatially varying sorption properties, and the influence of sorption processes on the synodic oscillation of the argon exosphere.