title: Atomic hydrogen on Mars: measurements at solar minimum.
abstract: The Copernicus Orbiting Astronomical Observatory was used to obtain measurements of Mars Lyman-alpha (1215.671-angstrom) emission at the solar minimum, which has resulted in the first information on atomic hydrogen concentrations in the upper atmosphere of Mars at the solar minimum. The Copernicus measurements, coupled with the Viking in situ measurements of the temperature (170 degrees +/- 30 degrees K) of the upper atmosphere of Mars, indicate that the atomic hydrogen number density at the exobase of Mars (250 kilometers) is about 60 times greater than that deduced from Mariner 6 and 7 Lyman-alpha measurements obtained during a period of high solar activity. The Copernicus results are consistent with Hunten's hypothesis of the diffusion-limited escape of atomic hydrogen from Mars.
authors.forename: J S
authors.initials: JS
authors.lastname: Levine
authors.forename: D S
authors.initials: DS
authors.lastname: McDougal
authors.forename: D E
authors.initials: DE
authors.lastname: Anderson
authors.forename: E S
authors.initials: ES
authors.lastname: Barker