Analysis of the Doppler tracking data near encounter yields a value for the ratio of the mass of the sun to that of Venus of 408,523.9 +/- 1.2, which is in good agreement with prior determinations based on data from Mariner 2 and Mariner 5. Preliminary analysis indicates that the magnitudes of the fractional differences in the principal moments of inertia of Venus are no larger than 10(-4), given that the effects of gravity-field harmonics higher than the second are negligible. Additional analysis is needed to determine the influence of the higher order harmonics on this bound. Four distinct temperature inversions exist at altitudes of 56, 58, 61, and 63 kilometers. The X-band signal was much more rapidly attenuated than the S-band signal and disappeared completely at 52-kilometer altitude. The nightside ionosphere consists of two layers having a peak density of 10(4) electrons per cubic centimeter at altitudes of 140 and 120 kilometers. The dayside ionosphere has a peak density of 3 X 10(5) electrons per cubic centimeter at an altitude of 145 kilometers. The electron number density observed at higher altitudes was ten times less than that observed by Mariner 5, and no strong evidence for a well-defined plasmapause was found.

Dual‐frequency bistatic‐radar observations of the moon have been made using Apollo 14 and 15 spacecraft in lunar orbit. Simultaneous 13‐ and 116‐cm wavelength radio transmissions from the spacecraft were received on the earth after reflection from the lunar surface. The received data were processed to obtain complete polarization and power spectra of the echo signal; the ellipticity, orientation, and magnitude of the deterministically polarized part were obtained as a function of frequency. The polarized parts of the echo spectra were then reduced according to the theory of quasispecular scattering from a gently undulating surface. The unpolarized portions of the echo spectra were associated with a diffuse scattering mechanism. When adjusted to normal incidence, the ratio of polarized to unpolarized power is 8(+l, −3) db at the 13‐cm wavelength. Variations in the 13‐cm unpolarized power are on the order of 1 db. At 116 cm, variations in the ratio of polarized to unpolarized power are considerably larger, on the order of 5 db. In two regions, near Lalande δ and the northern portions of Hipparchus, the unpolarized power apparently exceeds the polarized power. The craters Lansberg, Bessel, and Euler are not detectable in their effects on the orientation and eccentricity of the polarization ellipse or on the unpolarized component. Within Mare Serenitatis and Oceanus Procellarum, the 13‐cm data follow a classical Fresnel reflection curve corresponding to relative dielectric constant ϵ = 3.1 ± 0.1. Over most of these same areas, the 116‐cm data are consistent with this value of relative dielectric constant. In some areas, however, notably between Reiner and Hevelius, there are marked deviations from the reflectivities predicted for ϵ = 3.1. These results cannot be explained on the basis of simple models employing contiguous, semi‐infinite, dielectric interfaces. In the highlands to the south and southwest of Mare Crisium, the relative dielectric constant obtained at 116 cm wavelength is ϵ = 2.8 ± 0.1. In this region, the 13‐cm data depart from the reflectivities predicted for simple dielectric interface. These departures may be explained in terms of models employing layered dielectric structures. In Oceanus Procellarum, a model that has a local minimum in density at depth of 2 to 4 meters is consistent with the data. Lunar rms slopes, as determined by the Gaussian equivalent method from the polarized frequency spectra, show systematic differences with respect to mare and highland units. Within the highlands, the rms slopes obtained at the two wavelengths are nearly equal and vary between tan 6° and tan 8°. Within mare units, rms slopes inferred from the 116‐cm data vary between tan 1° and tan 2°. Mare rms slopes at 13 cm are in the range of tan 2° to tan 4°. At the same location, the slopes obtained at the 116‐cm wavelengths are typically one‐half as large as those obtained at 13 cm. Using Hagfors' (1966) model for wavelength dependence, we conclude that on a 0.2‐ to 2‐meter surface scale, the mare are rougher than the...

Laboratory measurements on the electrical properties of solid carbon dioxide (dry ice) were made over the frequency range 2.2 to 12 GHz. These give a dielectric constant which varies with density according to the Rayleigh mixing formula and is independent of frequency; at 1 g/cm 3 the dielectric constant is 1.7.The loss tangent was below the sensitivity threshold of our measurement technique at all frequencies and densities used; we set an upper limit of 0.005.

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