First results of the Mariner-6 radio occupation measurement of the lower atmosphere of Mars

As the radio signal of Mariner 6 was intercepted by the surface of Mars near Meridiani Sinus, the presence of an atmosphere caused small changes in the frequency of the received signal. Analysis of these changes indicates that the pressure at the surface of Mars at that point is about 6.6 mb and the temperature approximately 276°K. Data taken as the radio beam emerged from behind Mars in the vicinity of the north pole indicate a surface pressure of approximately 6.4 mb and a temperature of about 158°K. Extrapolation of the 6.6-mb pressure measurement at the point of entry over the 12-km range of topological variation measured by earth-based radars indicates that the surface pressure in the near north equatorial regions of Mars may vary from about 3 to about 8 mb.