Pioneer 10 ultraviolet photometer observations of the interplanetary glow at heliocentric distances from 2 to 14 AU

An analysis is presented of the observed Pioneer 10 interplanetary data from 1972 to 1977, taking into account the interplanetary glow intensity observed by the Pioneer 10 UV photometer at sun-spacecraft distances of 2-14 AU. On the basis of the obtained data, it was determined that the background intensity for the 200-1400 A band pass of the photometer channel is about 40 + or - 10 R, and that the nearby interstellar density is 0.04 + or - 0.91 per ccm for hydrogen and about 0.01 + or - 0.002 per ccm for helium. Accordingly, the He/H number density is about 0.25 at large distances from the sun. The Pioneer 10 spacecraft is leaving the solar system in the downwind direction, while both Pioneer 11 and Voyager will leave in the upwind direction. The combined UV observations of the interplanetary glow will provide accurate results on the physical status of the inflowing interstellar gas and the variability of background radiation as well.