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Science 23 September 1966:
Vol. 153. no. 3743, pp. 1518 - 1523
DOI: 10.1126/science.153.3743.1518
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Articles

Atmosphere of Mars: Mariner IV Models Compared

Gunnar Fjeldbo 1, Wencke C. Fjeldbo 1, and Von R. Eshleman 1

1 Center for Radar Astronomy, Stanford University, Stanford, California

Three classes of models for the atmosphere of Mars differ in identifying the main ionospheric layer measured by Mariner IV as being analogous to a terrestrial F2, F1, or E layer. At an altitude of several hundred kilometers, the relative atmospheric mass densities for these models (in the order named) are approximately 1, 102, and 104, and the temperatures are roughly 100°, 200°, and 400° K. Theory and observation are in best agreement for an F, s model, for which photodissociation of CO2, and diffusive separation result in an atomic-oxygen upper atmosphere, with O+ being the principal ion in the isothermal topside of the ionosphere. The mesopause temperature minimum would be at or below the freezing point of CO2, and dry ice particles would be expected to form. However, an F1 model, with molecular ions in a mixed and warmer upper atmosphere, might result if photodissociation and diffusive separation are markedly less than would be expected from analogy with Earth's upper atmosphere. The E model proposed by Chamberlain and McElroy appears very unlikely; it is not compatible with the measured ionization profile unless rather unlikely assumptions are made about the values, and changes with height, of the effective recombination coefficient and the average ion mass. Moreover our theoretical heat-budget computations for the atmospheric region probed by Mariner IV indicate markedly lower temperatures and temperature gradients than were obtained for the E model.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Atmosphere and Ionosphere of Venus from the Mariner V S-Band Radio Occultation Measurement.
A. Kliore, A. Kliore, G. S. Levy, D. L. Cain, G. Fjeldbo, and S. I. Rasool (1967)
Science 158, 1683-1688
   Abstract »    PDF »
Radar Astronomy: Rotation rates of Venus and Mercury and density of the atmosphere of Mars are recent radar discoveries.
V. R. Eshleman (1967)
Science 158, 585-597
   PDF »


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