Open AccessThe interstellar hydrogen shadow: Observations of interstellar pickup ions beyond Jupiter
Author(s) -
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.
Publication year - 2004
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2003ja010217
Subject(s) - physics , pickup , heliosphere , solar wind , jupiter (rocket family) , interstellar medium , astronomy , solar system , astrophysics , ionization , radiation pressure , ion , plasma , galaxy , spacecraft , quantum mechanics , artificial intelligence , computer science , image (mathematics)
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.