During the 1971 opposition of Mars, new infrared spectra covering the region 1800–3200 cm−1 (3.1–5.6μ) were taken at a resolution of 0.095 cm−1 using a Connes'-type Fourier spectrometer on the 2.7 m telescope, McDonald Observatory. Spectra were obtained near 6° and 33° phase and were calibrated against the Sun, standard stars and an internal black body.

No new trace constituents have, as yet, been found in the spectra, but several previously unobserved combination and isotopic bands of CO2 are visible. It has also been found possible to fit fairly well defined kinetic temperatures and Bond albedos to the two sets of data. The kinetic temperatures have been determined by a new technique. It is found that the albedo at 33° phase, which was determined a few days after the onset of the great dust storm of 1971, was significantly higher than for the clear atmosphere. The explanation for this phenomenon must await detailed radiative transfer calculations for a dust-laden atmosphere.

The purpose of this paper is to give an updated report on several recent findings concerning Mars obtained from studies now in progress at the Planetary Research Center of Lowell Observatory. In this work, extensive use has been made of ground-based images obtained almost hourly by seven observatories cooperating under the International Planetary Patrol Program (Baum, 1973).

A critical analysis of selected high-quality photometric observations of Mars indicates that: (1) The phase function is concave upward out to at least 40° phase. No sudden brightening occurs at opposition, but the curvature increases at small phase. (2) Large systematic differences (0.1–0.2 mag.) exist between different observers' data. However, the small random scatter attributable to Mars (0.01–0.02 mag.) in the better series suggests that these differences represent systematic errors in data reduction, not variations in the planet's brightness. (3) The disentangling of seasonal, diurnal, and phase effects leaves considerable ambiguity; more observations are needed, over a long time, with a stable instrumental system. However, even the present data are sufficient to expose substantial errors in published phase curves of Mars (and consequently, in interpretations based on them).

The results of detailed photometric treatment of Mars photographs obtained with the Automatic Interplanetary Station ‘Mars 3’ in three wavelengths are given. Photometric maps of the Martian surface have been constructed; a thin layer observed near the limb has been investigated.

Over 20000 thermal emission spectra of Mars have been obtained, providing extensive diurnal, seasonal and spatial coverage of the planet. Each spectrum covers the spectral range from 200 to 2000 cm−1 with an apodized spectral resolution of 2.4 cm−1; the noise equivalent radiance of the instrument is 0.5 × 10−7 W cm−2 sr−1 (cm−1)−1.

The radio occultation technique, consisting of the observation of changes in the phase, frequency, and amplitude of a radio signal from a spacecraft as it passes through the atmosphere of a planet before and after occultation, was first applied to measure the atmosphere of Mars with the Mariner IV spacecraft in 1965. The interpretation of these changes in terms of refraction of the radio beam by the neutral atmosphere and ionosphere of the planet provided the first direct and quantitative measurement of its vertical structure and established the surface atmospheric pressure of Mars as lying between 5 and 9 mb. The presence of a daytime ionosphere with a peak electron density of about 105 el cm−3 was also measured. The Mariner VI and VII spacecraft flew by Mars in 1969 and provided an additional four measurements of the atmosphere and surface radius of the planet. They confirmed the surface pressure values measured by Mariner IV and provided data for a crude estimate of the shape of the planet.

By far the greatest volume of radio occultation information on the atmosphere and surface of Mars was returned by the Mariner IX orbiter which was placed in orbit about Mars in November of 1971. During three occultation episodes in November-December 1971, May-June 1972, and September-October 1972, the Mariner IX mission provided 260 successful radio occultation measurements.

The early measurements, made at the time of the Martian dust storm of 1971, showed greatly reduced temperature gradients in the daytime troposphere, indicating the heating effect of the dust. The temperature gradients that were measured later in the mission, when the atmosphere was apparently free of dust, were still much lower than expected under conditions of radiative-convective balance, indicating that dynamics may play a large part in determining the temperature structure of the Martian troposphere. Temperatures taken at night near the winter poles were consistent with the condensation of carbon dioxide.

The surface atmospheric pressure was observed to vary widely with topography ranging from about 1 mb at the summit of the Middle Spot volcano (Pavonis Mons) to over 10 mb in the North circumpolar region. In the South equatorial region the highest surface pressure of about 9 mb was measured at the bottom of the Hellas basin.

The radius of the planet was measured with accuracies ranging from about 0.25 to about 2.1 km over latitudes ranging from 86° to −80°. These measurements have shown that Mars has pronounced equatorial and north-south asymmetries, which make it difficult to represent its shape by a simple triaxial figure.

The daytime ionosphere measurements indicated that the main ionization peak was similar in behavior to a terrestrial F1 layer and is probably produced by photoionization of carbon dioxide by solar extreme ultraviolet. Comparison of the heights of the maximum between the early data taken in November-December, 1971, and the Extended Mission of May-June 1972, showed that the lower atmospheric temperatures decreased by about 25%, which is consistent with clearing of the atmosphere.

The experience gained from Mars radio occultation experiments suggests that the quality of data can be significantly improved by such features of the spacecraft radio system as a stable oscillator, dual frequency downlink capability, and a steerable high-gain antenna.

A hydronamical theory describing the motion of the dusty flow including the effects of thermal stratification is presented. It is shown that the dust, while decreasing the intensity of turbulence in the flow, can accelerate the wind. Applied to Mars, the theory reveals that these effects may be important there in understanding the nature and the long duration of Martian dust storms.

The theoretical bases for deducing the solar abundance of helium from the determination of the H2/He mixing ratio in the giant planets are examined. The present state of the determination of the helium abundance is given. Experimental methods used to evaluate the H2/He ratio in the giant planets are critically reviewed. Methods in prospect are also briefly exposed.

Since Jupiter and Saturn are considered to be composed primarily of hydrogen, its pressure-density equation of state is needed for computational models of their interiors. Until recently, experimental data were limited to 20 kbar statically and 40 kbar dynamically. Since the majority of a major planet is at a pressure in excess of this, there were only theoretical calculations available for modeling.

Wigner-Seitz type calculations have been shown to be accurate at determining the equations of state of the alkali metals. Hence, it has been assumed that the equation of state of metallic hydrogen can be calculated in the same way with fair confidence. However, the molecular hydrogen equation of state has been much more ellusive. The many attempts at modeling the interatomic forces have led to rather scattered pressure density relationships.

The planetary model situation is further complicated by the expectation that the transition from the molecular to the metallic phase will be in conjunction with a relatively large density change.

Recently, data from new experiments have become available; in one case up to 8 Mbar. The data are not in disagreement with many calculations on hydrogen, but the resolution is not yet adequate to determine accurately and confidently, the pressure and the densities of the molecular to metallic phase transition. The accuracy of these parameters in turn affect the models of the planetary interiors, such as the radii of the metallic sphere and high density core.

This paper will discuss the details of these relations and the possible affects of the speculative properties of metallic hydrogen.

A recent theoretical study of the structure and evolution of Jupiter (Graboske et al., 1974b) is based on a three-stage model of Jovian evolution. The central phase, gravitational contraction of an adiabatic, homogeneous convective fluid system, begins early in solar system evolution and lasts for times of the order of 2 × 109 yr. Good agreement with observed radius and luminosity is achieved for a model with a solar mixture composition. The surface boundary layer has a dominant influence on the evolutionary timescale. Surface boundary factors which are important are the solar energy input, a function of the solar luminosity and the planetary albedo, and the detailed physics of the superadiabatic zone, which depends on the variation of opacity and ∇ad with depth. The evolutionary study demonstrates that the current planet cannot be an adiabatic homogeneous fluid throughout. The inclusion of a superadiabatic zone is necessary, and the existence of a heterogeneous (gravitationally layered) fluid interior is possible.

We have made high resolution scans of the Jovian H2 4–0 S(1) line at 6367.75 Å and the 3–0 S(1) line at 8150.67 Å, in an attempt to establish improved equivalent widths and to measure any spatial-temporal variations across the disc. Preliminary analysis indicates that temporal changes in the 3–0 S(1) line can be as large as about 40% over a period of about a week; furthermore, this line is systematically weaker at the limb (about 10%) and stronger at the poles (about 20%) than it is at the center of the disc. The 4–0 S(1) line shows very little temporal change, but does have a similar center to limb variation. Current theoretical models of line formation and cloud structure on Jupiter are not able to explain the observed variations although it is clear that some sort of two-layer model is necessary.

Three spectra of Jupiter were recorded by TD1A satellite between 1350 and 2600 Å. From these data, the geometrical albedo of the planet was computed.

From 2600 to 2100 Å, the value of the albedo matches the simple diffusing models of Jupiter's atmosphere (Greenspan and Owen, 1967).

From 2100 to 1800 Å, a broad absorption can be assigned to NH3 molecule (2168 Å transition).

Another absorption commences below 1800 Å. The absorbing molecule involved will be determined at a later date.

High resolution spectra of Jupiter and Saturn were obtained with a Fourier Transform Michelson interferometer. A comparison of the observed spectra, after elimination of the solar and terrestrial contributions to absorption, with synthetic profiles for the reflecting layer model has permitted new determinations of the Lorentz half-width, the methane abundance, the rotational temperature and the pressure at the level of formation of the methane lines for both Jupiter and Saturn.

The existence of a small dipole moment in the vibronic ground state of methane leads to transitions in the microwave spectral range. Frequencies and line strengths appropriate to the atmospheres of the outer planets are presented.

It is shown through the use of weighting functions that Jupiter's brightness temperature in the wavelength range 0.8–1.5 cm contains information on the thermal structure and abundance of ammonia in and above the tropopause in Jupiter's atmosphere. We present new data of Jupiter's brightness temperature in this wavelength range, and compare the results with theoretical spectra. The pressure in the Jovian atmosphere is estimated from these data to be 0.48 atm at 130K.

Models of Jupiter's radiation belts have been constructed to determine the distribution of particles and their energies which will produce the observed decimetric radio emission. Data on the spectrum and the variation of emission with Jovian longitude have been used to show that the relativistic particles have a nearly isotropic distribution with high energies (of order 100 MeV) within 2 Jovian radii and a very flat distribution in the equatorial plane of low energy particles further out in the magnetosphere.

Subtraction of the emission predicted by this model from the total radio emission shows that the thermal contribution in the frequency range between 3000 and 10000 MHz is somewhat less than had been previously expected. (The brightness temperature of the planetary disk is 180 K at 3000 MHz, for example.) This suggests that the ammonia mixing ratio in Jupiter's upper atmosphere may be as high as 0.002.

Realistic inhomogeneous models of Jupiter's lower atmosphere are used to interpret recent observations of the (3–0) and (4–0) H2 quadrupole lines at different portions of the visible disc of the planet. The time variations of these observations are analysed in terms of changes in the cloud structure.

Recent contributions to the dynamics of Jupiter's atmospheres were reviewed under the following headings: (a) general magnitude of winds and temperature fluctuations; (b) cloud bands and zonal velocity profile (including equatorial jet); (c) transient non-axisymmetric features (spots, and irregular markings); (d) the Great Red Spot.

The aim of this paper is to present results of temperature and density profiles of the upper atmosphere of Jupiter as deduced from observation of the occultation of β Sco on May 13, 1971.

The occultation light curve of β Sco is shown. The analysis of data is based on the Abelian integral inversion. Jovian refractivity profiles and typical temperature and density profiles are also shown.

The extent of the atmospheric zone where results are significant is discussed.

It is shown that no valid information about the thermosphere has been obtained.

Twelve eclipse light curves for the Galilean satellites have been observed at 30 colors. The shape of the curves depend upon Jovian atmospheric properties such as Rayleigh scattering, aerosol distribution, molecular absorption, scale height and cloud top altitude, as well as the satellite diameter. Different zenographic latitudes and longitudes along the sunrise and sunset terminator have been observed. Very long absorption path lengths are obtained compared to normal incidence because of the tangential passage of the Sun's rays. Refractive tails are observed in most cases which allow aerosol distributions to be determined. The other atmospheric properties may also be derived.