Atmospheric mass loss from Titan by sputtering

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Abstract Previous investigations by the authors of non-thermal escape processes such as dissociative recombination of N 2 + ions and impact dissociation of N 2 by magnetospheric electron precipitation of solar e.u.v. photons have shown nitrogen escape rates much lower than originally estimated from Voyager 1 observations, according to which 10% of Titan's atmospheric mass could have been lost over the past 4.5 billion years. Here, the erosion of Titan's nitrogen atmosphere resulting from sputtering, due to energetic particles occurring when Titan is either in the solar wind or in Saturn's magnetosphere, is investigated. Sputtering from Titan's nitrogen atmosphere leads to an escape rate of about 3 × 10 25 N atoms s −1 when solar wind protons are the responsible cause, and to about 7 × 10 26 N atoms s −1 when magnetospheric particles in Saturn's magnetosphere are considered. Thus, the total atmospheric mass loss over the age of the Solar System by sputtering would amount to about 20% of the present atmospheric mass of Titan. In contrast to impact ionization/dissociation, there will be no extended atomic nitrogen corona present above Titan, since for sputtering the excess energy leads primarily to escape and supply to the Saturn system rather than to ballistic orbits. Sputtering will yield, however, a small N 2 corona of Titan.