Evolution of Titan's atmosphere due to the solar wind interaction

Earth-based observations of anomalies of heavy isotopes such as ¹⁵N/¹⁴N in Titan's atmosphere indicate strong enrichments in the heavy constituents. Previous studies which tried to explain these anomalies suggest that Titan's upper atmosphere should have been exposed to a much stronger plasma interaction than today. Astrophysical observations and studies on radiative fluxes, stellar magnetic fields, stellar winds of solar-type stars with different ages and lunar and meteorite fossil records indicate that our early Sun underwent indeed a highly active phase after its formation. Because the evolution of atmospheres must be understood within the context of the evolving solar particle flux we estimated the solar wind density and velocity over Titan's history. For reconstructing the evolution of the solar wind mass flux we use recent observational data of stellar winds from several solar-like stars with different ages. Our study indicate that Saturn's magnetosphere was highly compressed during most of its lifetime to distances smaller than Titan's orbital radius. Because the early Sun had a much denser solar wind mass flux up to 1000 times higher than today, we investigate various atmospheric erosion processes over Titan's history which may have been responsible for high atmospheric loss rates and the isotope fractionation observed at present. Future studies will include the in-situ measurements of further isotope anomalies hopefully obtained by the Gas Chromatograph and Mass Spectrometer (GCMS) instrument on board of the Huygens probe, which will help to find a better solution of the mystery of Titan's isotope anomalies. This approach is important for estimations of the total nitrogen reservoir required to produce the present Titan atmosphere.