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The interstellar hydrogen shadow: Observations of interstellar pickup ions beyond Jupiter
Southwest Research Institute, San Antonio, Texas, USA
Southwest Research Institute, San Antonio, Texas, USA
Southwest Research Institute, San Antonio, Texas, USA
Southwest Research Institute, San Antonio, Texas, USA
Southwest Research Institute, San Antonio, Texas, USA
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
CNRS, St. Maur, France
KFKI Research Institute for Particles and Nuclear Physics, Budapest, Hungary
Mullard Space Science Laboratory, University College London, Surrey, UK
This study analyzes the first direct, mass-resolved observations of heliospheric pickup ions beyond the orbit of Jupiter. The Cassini Plasma Spectrometer observes H+, He+, He++, and O+ pickup ions of interstellar origin between 6.4 and 8.2 AU. Cassini's trajectory carries it through the downstream direction where we observe enhancements in the pickup He consistent with gravitational focusing by the Sun. We also show the first in situ observations of an “interstellar hydrogen shadow” where pickup H is depleted in the region behind the Sun relative to the local interstellar flow. Most H atoms cannot penetrate into this downstream shadow region both because the outward force due to radiation pressure exceeds gravitational attraction at this time and because H atoms trying to enter the shadow must pass close by the Sun where they have a high probability of being ionized and swept out with the solar wind.
Received 28 August 2003; accepted 17 November 2003; published 5 February 2004.
Citation: (2004), The interstellar hydrogen shadow: Observations of interstellar pickup ions beyond Jupiter, J. Geophys. Res., 109, A02104, doi:10.1029/2003JA010217.
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