Radio Occultation Measurements of The Mars Atmosphere with Mariners 6 and 7

Abstract

An analysis of the Mariner 6 and 7 occultation data has been completed. Final profiles of temperature, pressure, and electron density have been obtained for the Mariner 6 and 7 entry and exit cases, and results are presented for both the lower atmosphere and the ionosphere. The results of a detailed analysis of the systematic and formal errors introduced at each stage of the data reduction process are also included. At all four occultation points, the lapse rate of temperature was subadiabatic up to altitudes in excess of 20 km. A pronounced temperature inversion was present above the surface at the Mariner 6 exit point. All four profiles exhibit a sharp, superadiabatic drop in temperature at high altitudes, with temperatures falling below the frost point of CO2. These results give a strong indication of frozen CO2 in the middle atmosphere of Mars. The analysis for the upper atmosphere indicates peak electron populations of 1.59±0.2×105 cm−3 near 137 km and 1.73±0.2×103 cm−3 near 138 km, at the Mariner 6 and 7 entry points, respectively. The plasma scale heights above these maxima were 43±6 and 47±4 km, corresponding to average topside temperatures of 388±54 and 424±35°K, for Mariner 6 and 7 entries, respectively.

Clouds in the Martian Atmosphere

“…Simple models of the thermal state of the polar night atmosphere had also shown that CO condensation should be possible and that the atmosphere should also be thermodynamically in equilibrium with the surface condensates, and thus in a saturated state. This was putatively observed in the Mariner 6 flyby exit radio occultation acquired at high northern latitudes that showed atmospheric temperatures close to saturation near the surface, and that the atmosphere was supersaturated also above 10 km altitude (Hogan et al, 1972).…”

MGS electron density profiles: Analysis and modeling of peak altitudes

“…The E-region peak is usually seen as a shoulder on the lower side of the F 1 peak or as a more-or-less distinct peak below a small minimum in the electron density profile. This is also true for most of the RO electron density profiles returned from earlier spacecraft, such as the Mariner 6 and 7 flybys (e.g., Fjeldbo and Eshleman, 1968, Fjeldbo et al, 1970, Hogan et al, 1972; the Soviet Mars-2 orbiter, and the Mars-4 and Mars-6 flybys (e.g., Kolosov et al, 1973, Vasil'ev et al, 1975; the Mariner 9 orbiter (e.g., Kliore et al, 1972aKliore et al, , 1973Kliore, 1974); and the Viking 1 and 2 orbiters (e.g., Lindal et al, 1979;Kliore, 1992;Zhang et al, 1990). These early missions returned fewer RO profiles, but in general, they covered a greater range of SZA, for which the geometrical minimum is near 45°.…”

First measurements of composition and dynamics of the Martian ionosphere by MAVEN's Neutral Gas and Ion Mass Spectrometer

“…CO 2 + altitude profiles were also derived from the dayglow measurements of Mariners 6 and 7 [ Krasnopolsky , ]. Electron density profiles of the Martian ionosphere were collected by radio occultation and radar sounding experiments on several entry probes and orbiters, including Mariner 4, 6, 7, and 9 [ Fjeldbo and Eshleman, ; Hogan et al, ; Kliore et al, ], Mars 2, 3, 4, and 6 [ Kolosov et al, ; Vasilev et al, ], Viking 1 and 2 [ Lindal et al, ], and more recently by the Mars Global Surveyor [ Tyler et al, ], and Mars Express [ Pätzold et al, ; Gurnett et al, ]. While radio occultation and radar sounding data do not carry information on ion composition, when taking collectively, they provide a global view of the spatial structures and dynamics of the ionosphere.…”