ATMOSPHERES OF EARTH, MARS, AND VENUS, AS DEFINED BY ENTRY PROBE EXPERIMENTS

In 1963, it was proposed that small spacecraft be sent to Mars and Venus to define the structure of their atmospheres. The capabilities of such atmospheric probes were demonstrated by the Planetary Atmosphere Experiments Test in the Earth's atmosphere in 1971. The techniques developed were subsequently applied in experiments on the Viking Landers at Mars in 1976 and at Venus on the four Pioneer Venus Probes in 1978. The Mars and Venus results made major contributions to the current working definition of these atmospheres. They yielded not only the first-order parameters of atmospheric structure, i.e., the profiles of temperature, pressure, and density with altitude, but also insights into some basic meteorological conditions in those atmospheres, such as atmospheric stability, the presence of waves and turbulence, and the evaluation of thermal contrasts on a global scale. This paper reviews the results obtained from these experiments and outlines the concepts and approaches employed.