DETERMINATION OF INTERSTELLAR PICKUP ION DISTRIBUTIONS IN THE SOLAR-WIND WITH SOHO AND CLUSTER

Over the last 10 years, the experimental basis for the study of the lo cal interstellar medium has been substantially enhanced by the direct detection of interstellar pickup ions and of interstellar neutral heli um within the heliosphere. Pickup ions can be studied for a wide range of interstellar species. However, currently the accuracy of the metho d to determine the parameters of the interstellar medium, namely neutr al density, temperature and relative velocity, is hampered by two prob lems: (1) in most cases the crucial ionization rates are not available from simultaneous measurements and (2) the transport of the pickup io ns in the interplanetary medium substantially modifies the measured sp atial distribution of the ions. In this study we will discuss how the enhanced capabilities of the instrumentation on SOHO and Cluster in co mbination with ongoing efforts to model the pickup ion distributions w ill lead to a significant improvement over the coming years.