C+ PICKUP IONS IN THE HELIOSPHERE AND THEIR ORIGIN

C+ pickup ions were discovered with the solar wind ion composition spectrometer flying on Ulysses. Whereas the other nonlocally occurring pickup ions are produced from the interstellar gas penetrating deep into the heliosphere, C+ comes from an ''inner source'' which is located at a solar distance of a few AU and extends over all heliospheric latitudes investigated so far. The total production of C+, N+, and O+ by this inner source is of the order of 10(-3) relative to the total production of O+ from the interstellar gas in the heliosphere. Thus the inner source does not significantly contribute to oxygen or nitrogen in the anomalous cosmic rays (ACR), but its contribution to ACR carbon may not be negligible. We propose that the inner source material is carbon compounds evaporating from grains. At this time, the evidence points to interstellar as the major source, but we do not want to exclude yet a contribution from grains of solar system origin.