Detection of interstellar pick-up hydrogen in the solar system.
Interstellar hydrogen ionized primarily by the solar wind has been detected by the SWICS instrument on the Ulysses spacecraft at a distance of 4.8 astronomical units from the sun. This "pick-up" hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 +/- 0.015 and 0.013 +/- 0.003 per cubic centimeter, respectively.
Gloeckler
G
G
Galvin
A B
AB
Ipavich
F M
FM
Geiss
J
J
Balsiger
H
H
von Steiger
R
R
Fisk
L A
LA
Ogilvie
K W
KW
Wilken
B
B