A general similarity theory for dynamics of planetary atmospheres, which gives results consistent with those of more complex theories, is briefly outlined.

Four classes of manifestations of cloud activity observed in 1937 and 1969 near the autumn equinox of the northern hemisphere (165°< Ls < 192°) are discussed: (1) formation of the north polar haze cap, (2) unusual cloud systems on the disk, (3) recurrent or persistent cloud activity at the sunset limb, (4) clouds seen in projection above the sunrise terminator.

A search of several thousand plates in the Lowell Observatory collection yielded 28 groups of plates on which the positions of well-defined transient bright spots (often assumed to be clouds) could be followed on a nearly daily basis. These groups of plates were from 15 different oppositions of Mars, starting from 1907 and ending with 1958. All but two of these spanned four nights or more, and the maximum interval covered was thirty nights. Whether they appeared to show motion or not, the successive positions and shapes of all apparently associated bright spots or clouds were plotted on Mercator projections with the use of a projection plate reader especially designed at the Planetary Research Center for planet image studies of this kind. Clouds near the limb were avoided.

The 28 groups of plates yielded 95 cloud histories. More than half appeared to be relatively stationary. Others showed definite motion well in excess of observational error but sometimes followed paths that partly doubled back upon themselves. The mean velocity for non-stationary clouds was found to be 5.6 km per hour, and the most commonly occurring direction of motion was eastward, particularly at high latitudes. The range of velocities found by this mapping procedure is nearly an order of magnitude smaller than values that have been estimated earlier by others from visual observations. These earlier observations are evidently in error, unless there exist clouds at high elevation, visible only on the limb, that can move much faster than those that were mapped from this photographic survey. More clouds were found in the northern hemisphere than in the southern, and there seemed to be an avoidance of the relatively darker areas of the Martian surface. Certain regions seem to be more favored than others. A few recurrences at identical positions suggest the existence of related topographic features.

By the observations of Mariners and Veneras, oxygen atom deficiencies and very low exospheric temperatures were found in the upper atmospheres of Mars and Venus. There are two types of interpretations for these phenomena: photochemical ones (CO3 hypothesis), and dynamical ones. In this paper, the latter point of view is summarized. It was emphasized that the effect of atmospheric mixing due to general circulation and/or eddy diffusion is important for the understanding of the Cytherean and Martian atmospheric phenomena.

Quantitative calculations are presented of the intensities of the CO2+ bands present in the dayglows of Mars and Venus and it is argued that fluorescent scattering by CO2+ ions and photoionization of CO2 are the main sources of excitation. An estimate is made of the intensity of 3914 Å emission that would arise if the atmosphere contained N2.

Observations of Jupiter by multicolor photoelectric photometry in 10 narrow bands between 3150 Å and 1.06 μ and in UBV showed a brightening for shorter wavelengths in 1965 relative to 1963. An opposite effect occurred for the band at 7300 Å. These results are consistent with observed activity in the Jovian atmosphere. No obvious correlation could be found between brightness fluctuations and longitude of the central meridian, indicating that the activity was uniform in longitude or occurred on time scales short compared to a month.

Preliminary results from our study of Jupiter's equatorial limb darkening at 8–14 μ indicate that the effective temperature of the equatorial belt lay between 140 K and 150 K. We find these temperatures to be insensitive to the likely range of the He/H2 ratios. These results assume that Jupiter's only significant sources of extinction at these wavelengths are the pressure-induced absorption of H2 and He and the absorption of saturated NH3.

Measurements of the distribution of thermal flux along polar and equatorial scans across Jupiter suggest that the increase in brightness temperature near 8.5 μ observed by Gillett et al. may be caused by flux coming from near the cloud tops. Other possible sources are discussed and observational tests suggested which should clarify the thermal structure of the upper atmosphere.

If solid surfaces exist beneath the visible clouds of the major planets, they may be expected to exist at depths and pressures at which the component gas mixtures solidify under their own weight. The elucidation of phase behavior in mixtures of light gases at very high pressures is therefore essential to the solution of the problem of deep atmosphere structures in these planets. Available experimental evidence suggests several possible extrapolations of the H2-He phase diagram to high pressures. These have been used to develop a structural model for a H2-He atmosphere. In this model, gravitational separation of coexisting phases results in a layered structure, and it is shown that masses of H2-rich solid can exist in dynamic and thermodynamic equilibrium with a fluid layer of equal density but higher He content. This model forms the basis of a new hypothesis for Jupiter's Red Spot.

The presence of numerous near-commensurabilities among pairs of mean motions and the strong correlation between orbital radius and mass in the satellite systems of the three major planets (particularly in the Saturn system) suggest that the orbits of the satellites have evolved considerably under the action of tides. It is shown that the source of dissipation could be boundary layer turbulence at the base of the planetary atmosphere. If this is the source of dissipation then it should be possible to estimate the depths of these atmospheres from the mean rates of energy dissipation.

Spectrophotometric (photographic and photoelectric) measurements of the intensity of CH4 absorption bands at 6190 and 7250 Å over different regions of Saturn's disk show an increase in intensity toward the poles and a decrease toward the equatorial limb. In the bright equatorial belt of Saturn the methane absorption is about 25–28% less than in the south temperate belt (latitude about −20°).

Absolute photoelectric spectrophotometry of Saturn's disk gives a value for the single-scattering albedo of the aerosol particles at λ 6200–6500 Å at the center of the disk. Calculations of the curves of growth for the absorption lines formed in the thin gas and in the cloud layer were made and the comparison with observations of Jupiter and Saturn lead to the mean value of the volume scattering coefficient of the aerosol layer σa < 5 × 10−6 cm−1. In the equatorial region of Saturn σa is larger than in the temperate region by a factor 1.3 to 1.8.

The models of Saturn's atmosphere that fit well the observational data preclude the condensation of methane. An aerosol layer of ammonia is more probable in the atmosphere of Saturn. Calculations of the distribution of the ammonia aerosol volume density (Qa) give Qa ≃ 10−9 to 10−7 gm/cm3 for relative abundances of ammonia A = 10−6 to 10−4. Observational estimates of Qa derived from the values of σa give Qa < 10−9 gm/cm3. Apparently Saturn's atmosphere departs from conditions of ordinary convection.

Some very interesting variations in the spectral reflectivity of the different regions of Saturn are observed, especially in the ultraviolet. These data, as well as a systematic study of the methane absorptions in the near infrared strong bands are needed in future studies of Saturn's atmosphere.

Theoretical values of matrix elements of the quadrupole moment (Birnbaum and Poll, 1969; Dalgarno and Allison, 1969) and of the polarizability of H2 (Birnbaum and Poll, to be published) are used to calculate the integrated intensities of a number of lines in the pressure-induced overtone spectra of molecular hydrogen. These calculated intensities are used to obtain an estimate of the H2 abundance in the atmosphere of Uranus from the equivalent width of a feature in the 4-0 pressure-induced band observed by Giver and Spinrad (1966). An estimate of the equivalent width of the corresponding bands on Jupiter is also given.

Spectra of Uranus were obtained with the 122 cm reflector of the Crimean Astrophysical Observatory using the spectrometer of the Main Astronomical Observatory of the Ukrainian Academy of Sciences (Kiev), in March 1969. A photomultiplier (Soviet type 79) was used in a pulse counting mode, and the dispersion of the spectrometer at the camera focal plane was 15 Å/mm.

The satellite Titan is commonly quoted as possessing an atmosphere consisting of at least 2 × 104 cm atm of methane. Plausible additional atmospheric constituents like hydrogen and helium are assumed to have completely escaped from the satellite. However, the employment of recent techniques to the upper atmosphere of Titan permits an improved estimate of the upper limits of the hydrogen to methane and helium to methane mixing ratios existing in the lower atmosphere of Titan, namely 10−6±1 and 10−3.5±0.5.