The interstellar hydrogen shadow: Observations of interstellar pickup ions beyond Jupiter

D. J. McComas, N. A. Schwadron, F. J. Crary, H. A. Elliott, D. T. Young, J. T. Gosling, M. F. Thomsen, E. Sittler, J. J. Berthelier, K. Szego, A. J. Coates

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19 Citations (Scopus)


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.

Original languageEnglish
Article numberA02104
JournalJournal of Geophysical Research: Space Physics
Issue numberA2
Publication statusPublished - Feb 2004



  • Cassini
  • Heliosphere
  • Interstellar hydrogen shadow
  • Jupiter
  • Pickup ions

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Cite this

McComas, D. J., Schwadron, N. A., Crary, F. J., Elliott, H. A., Young, D. T., Gosling, J. T., Thomsen, M. F., Sittler, E., Berthelier, J. J., Szego, K., & Coates, A. J. (2004). The interstellar hydrogen shadow: Observations of interstellar pickup ions beyond Jupiter. Journal of Geophysical Research: Space Physics, 109(A2), [A02104].