title: Venus thermosphere and exosphere: first satellite drag measurements of an extraterrestrial atmosphere.
abstract: Atmospheric drag measurements obtained from the study of the orbital decay of Pioneer Venus 1 indicate that atomic oxygen predominates in the Venus atmosphere above 160 kilometers. Drag measurements give evidence that conditions characteristic of a planetary thermosphere disappear near sundown, with inferred exospheric temperatures sharply dropping from approximately 300 K to less than 150 K. Observed denisities are generally lower than given by theoretical models.
authors.forename: G M
authors.initials: GM
authors.lastname: Keating
authors.forename: R H
authors.initials: RH
authors.lastname: Tolson
authors.forename: E W
authors.initials: EW
authors.lastname: Hinson