Existing theories of planetary formation (based on a continuous solar nebula or on discrete objects) are briefly reviewed.

The report centers on general procedures applicable to the calculation of constitutive properties (equation of state and opacity) of media that serve as models for the solar nebula during planet formation and for the atmospheres of some planets. Specifically considered are the equilibrium compositions of a mixture of atoms, molecules, and their ionic species in the gaseous phase, condensation into grains with refractory cores and mantles of volatile compounds, and the ‘optical’ properties of the grain-gas medium. A summary of available and still needed basic (input) data and some currently available results are presented.

Grain accretion processes in a protoplanetary nebula have been studied regarding: (a) the distribution function of grain velocities; (b) electrostatic and electromagnetic mechanisms between grains. The velocity distribution function has been investigated for grains embedded in a turbulent gaseous medium. Results have been obtained for protoplanetary nebula densities ranging from 10−19 to 10−10 g cm−3. Considering interactions between two grains, photoelectrically charged by galactic ultraviolet flux and by charged-particle capture, and solid-solid interactions (dipole fluctuation effect), the authors estimate the physical cross section σ(v) with respect to the geometric one σ0. Then a statistical approach for an assembly of grains gives the accretion or destruction rates for these small particles. Therefore, according to their characteristic velocities, the following processes have been studied: rupture, fusion, vaporization.

The problem of escape of atmospheres from the Moon and planets has roots deep in ancient history. Many of the great philosophers of the past regarded the Earth's atmosphere as a medium extending to infinity, with a stationary Earth imbedded at the center. Indeed, it was this concept that led Ptolemy, among many others, to conclude that the Earth could not be moving, for otherwise it would be subject to a gale-force wind caused by its own motion. This idea fostered many of the early stories of interplanetary visitations. Lucian, for example, writing in the second century A.D., has his Icarome nippus fly to the Moon and beyond by means of wings attached to his body.

The scope of research in the field of high resolution infrared spectroscopy has expanded in numerous directions in recent years. Investigations of high resolution molecular spectra performed under controlled conditions in the laboratory are of significance to planetary studies because of the high resolution which one can achieve at the present time in the spectra of planets. In making use of laboratory data it is important to develop a proper perspective; due to technological advances the quality of experimental results has improved continuously during the past two decades, and, therefore, one has to exercise proper judgement when combining information from different laboratories. Somewhat detailed discussions are presented for the spectra of CO and CO2 to illustrate what modern measurements are capable of accomplishing. In the case of CO2, the extensive measurements of Courtoy and Herzberg done in the early 50's are not summarized in this paper because they are all consolidated in three previous publications. On the other hand, more recent measurements on CO2 are scattered in several publications and, therefore, an attempt has been made to collect them together in this article. This is not a comprehensive review paper but it is intended to provide only a glimpse into the expanding frontiers of research in high resolution infrared spectroscopy.

The laboratory techniques employed for the determination of optical constants are discussed briefly. The values obtained for the real n and imaginary k (or ni) parts of the refractive indices of water, ice, and liquid ammonia are presented graphically. Work currently in progress on solid ammonia and on sulphuric acid is discussed. Other approaches to studies of the properties of aerosols in planetary atmospheres are presented briefly.

The report contains a short description of the first Soviet-Polish space experiment, which has been accomplished aboard the ‘Intercosmos-Kopernik 500’ satellite, launched to commemorate the 500 anniversary of Copernicus birth. The purpose of the experiment is to observe sporadic radio emissions generated in the coronal and interplanetary medium at hectometric wave-length range and to measure parameters of the ionospheric plasma by means of the low- and high-frequency impedance probes. The idea of the experiments is presented together with the brief description of the measuring equipment and data recorded. First results of the space observations are shown. The correlation between electron density of the ambient plasma, ion-sheath capacitance of the aerial, and the upper hybrid frequency can be seen.

A historical account of observations of Venus and their interpretation is given. The major constituent of the atmosphere on Venus (CO2) was detected spectroscopically forty years ago, and minor constituents (CO, HF, HCl) have been found more recently. The infrared spectra also provide a means of studying the motions of her cloudy atmosphere. The composition of the clouds has been sought in the reflection spectrum of Venus, and some of the evidence for their nature is discussed.

From short wavelength (γ < 4 cm) interferometry of Venus interpreted on the basis of the physical structure and bulk composition of its atmosphere as given by spacecraft measurements, evidence for the presence of a source of opacity in addition to CO2 is found. This opacity presumably is due to unknown minor constituents of the atmosphere of Venus.

The systematic study of the distribution of the photon optical path in a finite scattering atmosphere gives the penetration depth of the radiation in a cloud; one can get then an accurate knowledge about the layer thickness in which the spectral line has been formed. The relation between the observed line frequency and the corresponding altitude is thus precisely expressed. The method is presented here with some preliminary results, it could be applied to the Venus, Jupiter and Saturne atmospheres to improve the knowledge of their clouds internal structure.

Using this method in case of Venus spectral lines it has been possible to deduce that for the Hansen's model, the optical depth of Venus clouds should be of the order of 40 and the cloud top closed to 70 km height.

The analysis of the sunlight scattered by Venus gives some insight upon its clouds. The measurements of polarized light are probably more sensitive to the nature of their constituents, and some recent studies seem to be able to give a satisfactory interpretation of this part of the scattered light. But the polarized light concerns the upper part of the clouds, and it is interesting to compare these results with intensity measurements. The phase curves, for the integrated light, leave some indeterminations, so we have studied if the intensity distribution on the Venus disk could give more accurate informations. This work, based on some plates kindly communicated by A. Dollfus, and analysed at Meudon Observatory, is more a preliminary investigation of the sensitivity of the method than an interpretation of the partial results presented. A simple model, of homogeneous plane parallel cloud, has been used, and the influence of various parameters has been tested (single scattering albedo, refractive index of particles and size distribution, optical depth of the cloud).

The influence of a dense molecular atmosphere under a cloud layer on spectral albedo of a planet is investigated. The lengths of paths of protons in the clouds are calculated. Experimental spectral transmission functions were used to calculate gas absorption. The results are compared with experimental data.

Measurements of the downward light flux during the descent from an altitude of 50 km to the ground have been made. Atmospheric layers with different optical thicknesses have been discovered. The optical properties of Venus atmosphere for different cloud models have been studied.

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of particles which have a narrow size distribution with a mean radius ~ 1 μ. The refractive index of the particles is 1.44 ± 0.015 at γ = 0.55 μ with a small normal dispersion, the refractive index decreasing from the ultraviolet toward the infrared. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb.

The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venus. A concentrated solution of sulfuric acid (H2SO4–H2O) provides good agreement with the polarization data.

The region of the 8200 Å Band of H2O was studied in spectra of Venus obtained with an echelle grating spectrograph operated at an altitude of 14.6 km in the NASA Learjet research aircraft. Taking advantage of low foreground absorption, observing at a time of velocity quadrature, differential spectroscopy with respect to lunar spectra, and spectrum averaging, we establish a value of H2O of 3 ± 20 μ for the total path over the entire disk. This value differs from earlier studies of the integrated disk but supports the low values recently derived from infrared bands and by very high spectral resolution groundbased studies.

These results establish that the average value over the entire disk is quite low but allows that locally larger values may exist as reported by Barker. A more complete description of this work appeared in Icarus21 (1974), 213.

The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 22° and 91°. Variations in the abundance have been found with both position and time. The total two-way transmission has varied from less than 5 to 77 μ of water vapor. Comparisons will be made between the water vapor abundances, presence of UV features, and the CO2 abundances determined from near simultaneous observations of CO2 bands at the same positions on the disk of Venus.

The amount of Martian atmospheric water vapor has been monitored during the past two years at McDonald Observatory using the échelle coudé scanner of the 272 cm reflector. Two periods of the Martian year have been monitored. The first period was during and after the great 1971 dust storm (L8 = 280° to 20° or summer in the southern hemisphere). The results obtained will be compared to the Mariner 9 IRIS and Mars 3 observations made during the same period.

During the second period (L8 = 124° to 266°) observations were made to follow the seasonal latitudinal and diurnal changes in the water vapor abundance in the Martian atmosphere. The water vapor abundance declines from a maximum of 20–35 μm at L8 = 125° to the 5–15 μm level at L8 = 180°. Then it remained relatively constant until L8 = 250° when the increase to 20–25 μm occurred in the southern latitudes. Studies of the latitudinal and diurnal water vapor distributions indicate the location of maximum and minimum abundances for this season are positively correlated with surface temperature variations.

We have searched for molecular lines in planetary atmospheres using the PEPSIOS spectrometer with an instrumental width about equal to that of the expected absorption line, and in the case of Jupiter, with the additional feature of Doppler compensation over the planetary disc.