Plasma-induced sputtering of an atmosphere

Near-surface oxygen atmosphere at Europa

“…Whereas the energetic ions (measured by the Galileo EPD; e.g., Cooper et al, 2001) for the most part pass through this thin atmosphere without collisions, the low energy plasma does not. Therefore, it can sputter the atmosphere (Johnson, 1990(Johnson, , 1994 Momentum transfer and dissociation collisions with high-energy magnetospheric ions lead to the kinetic energy transfer to 02 gas and formation of fresh suprathermal O atoms. This energy input to Europa's atmosphere causes additional atmospheric loss.…”

The Structure of Titan’s N2 and CH4 Coronae

“…We caution that the early DSMC results for Titan's atmospheric escape due to sputtering were based on limited pre-Cassini knowledge of the varying plasma environment of this satellite, and an updated analysis of sputter-induced escape is clearly deserved, taking advantage of the extensive measurements made over the past 10 years by several in situ plasma instruments on board Cassini(e.g., Arridge et al 2011a). However, we do not expect a substantial difference in the mean energy of escaping N 2 and CH 4 molecules since the physical processes leading to atmospheric sputtering are relatively well known (Johnson 1994). For N 2 , Shematovich et al (2003) reported a mean energy of 2eV for sputtering by incident magnetospheric ions and 7eV for sputtering by pick-up ions.…”

Sputtering of the atmosphere of Mars: 1. Collisional dissociation of CO2

“…The angular and energy distributions of the atoms and molecules ejected from an atmosphere by an incident ion or atom can be roughly separated into those species ejected in a single collision of the incident particle with an atmospheric particle and those ejected during the cascade of collisions initiated by an incident particle [Sieveka and Johnson, 1984;Johnson, 1990Johnson, , 1994. In the absence of dissociation, both the ejection efficiency (the yield) and the energy distribution of the ejecta are insensitive to the size of the collision cross section.…”

“…Further, Kass and Yung [1996] showed that even in a molecular atmosphere, if the collision dynamics are unchanged, an order of magnitude reduction in the principal dissociation cross section resulted only in a factor of 3 reduction in the sputter yield. However, transport calculations also show that the sputtering yields are sensitive to the angular dependence of the collision cross section, affecting the energy distribution of the recoils and the spatial distribution of energy deposition in the gas near the exobase (/3 and otSn, respectively, in the work by Johnson [1994]). These features should be well described by the results presented here or by a modified the solar fields and EUV flux in earlier epochs, the formation of and bombardment by pickup ions is a complex feedback process [Johnson and Luhmann, 1998] because the bombardment itself can change the composition and structure of the exobase and the corona.…”

“…Although the relative importance of these processes for the loss of an early, dense atmosphere is not settled, nonthermal atmospheric escape processes have been shown to produce sufficient loss to affect the evolution of the Martian atmosphere [e.g., Fox, 1993; Jakosky et al, 1994; Hutchins et al, 1997]. one such process, referred to as atmospheric sputtering [Johnson, 1994], is considered here.…”