INTERSTELLAR PICKUP HYDROGEN OBSERVATIONS AT LARGE HELIOCENTRIC DISTANCES

Possible signatures of interstellar pickup hydrogen have been identifi ed in data from the Pioneer 10 and 11 Ames plasma analyzers at locatio ns out to beyond the orbit of Saturn, and at a wide range of longitude s in the heliosphere, both upstream and downstream in the interstellar wind. These signatures provide an extension of pickup ion observation s out to beyond 15 AU heliocentric distance, including near where the maximum pickup hydrogen flux is expected. A depletion of interstellar pickup hydrogen downstream from the Sun in the interstellar flow may b e indicated. These signatures are consistent with Ulysses pickup ion m easurements.