title: Vertical structure of the ionosphere and upper neutral atmosphere of saturn from the pioneer radio occultation.
abstract: Radio occultation measurements at S band (2.293 gigahertz) of the ionosphere and upper neutral atmosphere of Saturn were obtained during the flyby of the Pioneer 11 Saturn spacecraft on 5 September 1979. Preliminary analysis of the occultation exit data taken at a latitude of 9.5 degrees S and a solar zenith angle of 90.6 degrees revealed the presence of a rather thin ionosphere, having a main peak electron density of about 9.4 x 10/(3) per cubic centimeter at an altitude of about 2800 above the level of a neutral number density of 10(19) per cubic centimeter and a lower peak of about 7 x 10(3) per cubic centimeter at 2200 kilometers. Data in the neutral atmosphere were obtained to a pressure level of about 120 millibars. The temperature structure derived from these data is consistent with the results of the Pioneer 11 Saturn infrared radiometer experiment (for a helium fraction of 15 percent) and with models derived from Earth-based observations for a helium fraction by number of about 4 to 10 percent. The helium fraction will be further defined by mutual iteration with the infrared radiometer team.
authors.forename: A J
authors.initials: AJ
authors.lastname: Kliore
authors.forename: G F
authors.initials: GF
authors.lastname: Lindal
authors.forename: I R
authors.initials: IR
authors.lastname: Patel
authors.forename: D N
authors.initials: DN
authors.lastname: Sweetnam
authors.forename: H B
authors.initials: HB
authors.lastname: Hotz
authors.forename: T R
authors.initials: TR
authors.lastname: McDonough