Comment on "Dayside Pickup Oxygen Ion Precipitation at Venus and Mars' Spatial Distributions, Energy Deposition, and Consequences"

The ejection of atoms and molecules from an atmosphere due to the energy deposited by plasma bombardment has been shown to play a role in the loss of species from certain planetary and satellite atmospheres. This ejection, often referred to as sputtering, can be produced by the bombarding plasma [Watson et al., 1980; McGrath and Johnson, 1987] and by locally generated "pickup ions" [e.g., Kozyra et al., 1982; Ishimoto et al., 1986; Luhmann and Kozyra, 1991]. Although the direct solar wind sputtering of Venus and Mars [Watson et al., 1980] was shown not to be significant compared to other loss processes [Hunten et al., 1989], Luhmann and Kozyra [1991] (LK) recently showed that the sputtering produced by pickup ions is not negligible. They used a particle transport code to calculate the ejected particle flux. However, in earlier work [Watson et al., 1980; Sieveka and Johnson, 1984; McGrath and Johnson, 1987], expressions developed for the sputtering of and ion penetration into condensed materials were used to describe sputtering from planetary atmospheres [e.g. Johnson, 1990]. Here the results of Luhmann and Kozyra [1991] are tested against these analytic expressions after a brief review.