In this research area, we focus on the interaction processes of solar/stellar radiation and plasma to the upper atmospheres of planets and bodies without atmospheres (e.g. Mercury, Moon(s), comets, asteroids, and planetary embryos). The evolution of planetary atmospheres from primordial, steam to secondary atmospheres are studied. The origin and escape of exospheres from airless bodies, and the effects on surface compositional modification are also investigated. Variations of isotopes and volatile elements in different planetary reservoirs keep information about atmospheric escape, composition and even the source of accreting material. For studying the evolutionary processes, known atmospheric isotope and elemental ratios are used for evolutionary reproduction attempts. The origin of Earth's N2-O2-dominated secondary atmosphere is studied in the framework of comparative planetology between Venus, Mars and potential terrestrial exoplanets. A better knowledge how Earth originated its biosphere will then also enhance our understanding of exoplanetary systems, in particular in view of the potential habitability of Earth-type exoplanets.

Figure a) shows the most likely proto-Earth accretion scenarios as constrained by different isotope-systematics (D-H, atmospheric Ar & Ne, primordial 3He abundance in the deep mantle) and isotopic chronometers (Hf-W, U-P) in dependence on the disk lifetime and activity of the young Sun by the IWF-team, inferred from several of their published research articles. Proto-Earth’s mass fraction during disk dispersal should have been ≈ 0.5 – 0.6 MEarth (dark grey area).

Figure b) shows the modelled upper atmosphere responses to present Earth's N2-O2-dominated atmosphere in comparison with Saturn's large moon Titan, a body in the outer solar system with a N2 atmosphere. The Earth's atmosphere would not have been stable against the higher soft X-ray and extreme ultraviolet radiation (XUV) of the young Sun during the first several hundred million years, indicating that its atmosphere had a different composition most likely CO2-rich.