In summary, we can conclude that the contributions of the different ionization processes to the total ionization rate for the most abundant interstellar species are basically known. The ionization of the noble gases He and Ne is almost completely dominated by photoionization, whereas for H charge-exchange with the solar wind is most important. For other species, such as 0 and Ar, both processes contribute significantly. Electron impact ionization can typically contribute by '" 10% to the total rate in the inner Solar System. Because direct measurements of the solar EUV flux are not yet...

This volume consists of papers developed from a joint ACE/ISSI symposium at the occasion of the eightieth birthday of Johannes Geiss. The symposium explored insights into the composition of solar-system and galactic matter that have been brought about by recent space missions, ground-based studies, and theoretical advances. Coverage includes linking primordial to solar composition, planetary samples, solar sources and fractionation processes, and interstellar gas and Cosmic rays.