Abstract

The precise radio tracking of the Mariner 5 spacecraft has enabled the distance from the center of Venus of the line-of-sight joining the tracking station and the spacecraft to be determined with an uncertainty of less than 0.2 km near the time of occultation. The resulting profiles of temperature and pressure, when superimposed on the data of Venera 4, indicate that the Soviet probe penetrated to a radial distance of about 6079 km from the center of mass of Venus. If this is assumed to be the radius of the solid surface of Venus, it is at variance with the results of earth-based planetary radar studies. Extrapolation to the radar radius leads to atmospheric models that are consistent with the results of passive radio astronomy. It is concluded that the Venera 4 probe either landed on a high plateau or surface feature undetected by radar, or did not continue its measurements to the surface of Venus.

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