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Coherently related S (2.3 GHz) and X band (8.4 GHz) signals transmitted from Voyager 1 and 2 have been used to probe the Jovian atmosphere during occultations of the spacecraft by Jupiter. The observations have yielded profiles in height of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere of Jupiter at latitudes ranging from 0° to about 70°S. The data cover a pressure range from 1000 to 1 mbar over a height interval of 160 km. At the 1000‐mbar level, the temperature was 165±5 K, and the lapse rate was equal to the adiabatic value of 2.1 K/km, within the resolution of the measurements. The ammonia abundance in this region of the atmosphere was about 0.022±0.008%, in approximate agreement with the value derived from cosmic abundance considerations. The tropopause, which was detected near the 140‐mbar level, had a temperature of 110 K. Above the tropopause, the temperature increased with increasing altitude, reaching 160±20 K in the 10‐ to 1‐mbar region of the stratosphere. Significant horizontal density variations were detected in the stratosphere. This may imply a nonuniform temperature and aerosol distribution across the Jovian disk or high‐ and low‐pressure regions due to local atmospheric dynamics. The zenoid or gravity equipotential surface which best fits the 100‐mbar isobaric surface has an equatorial radius of 71,541±4 km and a polar radius of 66,896±4 km.

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The equation of the parabolic ionosphere model is modified in a manner which introduces very slight changes in the electron-density distribution. Using this new "quasi-parabolic" (or QP) model, it is possible to derive exact expressions describing radio-ray trajectories without introducing the approximations which are needed when dealing with the parabolic ionosphere, although magnetoionic effects are not included. The consequent accuracy of computed rays is useful as an aid in evaluating the accuracy of more versatile ray-calculation methods. Also, the exact ray expressions can be of direct !lse in calculating slight differences between rays which are nearly identical, for in this process, small inaccuracies can become magnified.

Voyager 1 radio occultation measurements of Titan's equatorial atmosphere successfully probed to the surface, which is provisionally placed at a radius of 2570 kilometers. Derived scale heights plus other experimental and theoretical results indicate that molecular nitrogen is the predominant atmospheric constituent. The surface pressure and temperature appear to be about 1.6 bars and 93 K, respectively. The main clouds are probably methane ice, although some condensation of nitrogen cannot be ruled out. Solar abundance arguments suggest and the measurements allow large quantities of surface methane near its triple-point temperature, so that the three phases of methane could play roles in the atmosphere and on the surface of Titan similar to those of water on Earth. Radio occultation measurements of Saturn's atmosphere near 75 degrees south latitude reached a maximum pressure of 1.4 bars, where the temperature is about 156 K. The minimum temperature is about 91 K near the 60-millibar pressure level. The measured part of the polar ionosphere of Saturn has a peak electron concentration of 2.3 x 10(4) per cubic centimeter at an altitude of 2500 kilometers above the 1-bar level in the atmosphere, and a plasma scale height at the top of the ionosphere of 560 kilometers. Attenuation of monochromatic radiation at a wavelength of 3.6 centimeters propagating obliquely through Saturn's rings is consistent with traditional values for the normal optical depth of the rings, but the near-forward scattering of this radiation by the rings indicates effective scattering particles with larger than expected diameters of 10, 8, and 2 meters in the A ring, the outer Cassini division, and the C ring, respectively. Preliminary analysis of the radio tracking data yields new values for the masses of Rhea and Titan of 4.4 +/- 0.3 x 10(-6) and 236.64 +/- 0.08 x 10(-6) times the mass of Saturn. Corresponding values for the mean densities of these objects are 1.33 +/- 0.10 and about 1.89 grams per cubic centimeter. The density of Rhea is consistent with a solar-composition mix of anhydrous rock and volatiles, while Titan is apparently enriched in silicates relative to the solar composition.