Abstract: Papers on the photochemistry of the early atmosphere, the troposphere, stratosphere, and upper atmosphere are presented. Consideration is given to the effect of chemical constituents on the climate and atmosphere. Topics discussed include the composition of the atmospheres of Venus, Mars, the outer planets and their satellites, and the chemical changes which occur in comets.

Abstract: A novelty clock is provided wherein a spherical representation of the earth revolves about a stationary depiction of the sun at the face of the clock as would a second hand. While revolving about the sun, the earth also rotates upon its own axis which is angularly disposed to the straight line between sun and earth. The earth's motion, in conjunction with depictions of other planets of the solar system, provides an appealing and realistic visual effect. The motion of the earth is achieved by a mechanism driven by rotation of the shaft which would otherwise drive the second hand of the clock.

Abstract: The theory of a huge reservoir of comets (the “comet cloud”) extending to almost interstellar distances is analyzed, paying special attention to its dynamical stability, formation process and orbital properties of the incoming cloud comets. The perturbing influence of passing stars and giant molecular clouds is considered. Giant molecular clouds may be an important perturbing element of the comet cloud, although they do not seem to change drastically former studies including only stellar perturbations. The more tightly bound inner portions of the comet cloud, say within 104 AU, would have withstood the disrupting forces over the age of the solar system. The theory of a primordial comet origin in the outer planetary region close to Neptune’s orbit is specially analyzed. A primordial comet origin is consistent with the cosmogonic view that a large amount of residual material was ejected during the last stage in the formation of the Jovian planets. The smooth diffusion in the energy space of bodies scattered by Neptune guarantees that most of them will fall in the narrow range of energies close to zero (near-parabolic orbits) where passing stars and GMCs can act effectively on them. The long time scales of ~109 yr required for bodies scattered by Neptune to reach near-parabolic orbits would indicate that the buildup of the comet cloud was an event that took place long after the planets formed. Depending on the field of perturbing galactic objects, it is possible to conceive that most scattered comets were stored in rather tightly bound orbits (a ~104 AU), favoring the concept of their dynamical survival over several billion yr. Alternative theories of comet cloud formation, e.g. in-situ origin or interstellar capture, are also discussed. The main difficulty of the in-situ theory is to explain how comets could accumulate at large heliocentric distances where the density of the nebular material was presumably very low. The interstellar capture theory also meets severe dynamical objections as, for instance, the lack of observed comets with original strongly hyperbolic orbits and the extremely low probability of capture under most plausible conditions. Since our knowledge of the structure of giant molecular clouds and their frequency of encounters with the solar system is still very uncertain, the concept of capture of transient comet clouds during such encounters can be advanced very little beyond the speculative stage. Some other dynamical properties of relevance to theories of origin and structure of the comet cloud are also reviewed. We mention, for instance, the distribution of perihelion points on the celestial sphere. There seems to be here a well established deviation from randomness, although the debate on whether or not there is a preference of the perihelion clustering for the vicinity of the apex of the solar motion is still unsettled. The alleged correlation with the solar apex may be biased by the preference of comet discoveries in the northern hemisphere. Deviations from randomness might be caused by very close stellar passages in the recent past. The excess of retrograde orbits among the observed “new” and young comets — mainly those with q ≳ 2 AU — is another well known dynamical feature. Such as excess may probably be accounted for the by the combined action of planetary and stellar perturbation. Because of the decreasing action of planetary perturbations with increasing heliocentric distances, a significant increase in the rate of passages of long-period comets is predicted for the outer planetary region.

Abstract: Far-infrared spectrophotometry of Uranus and Neptune in the 30-55 micron spectral range is presented. The measurements in the present six independent spectral bands allow the derivation of atmospheric temperature profiles for these planets. Both planets are found to have tropopause temperatures near 53 K, with Neptune having a stronger stratospheric temperature inversion than Uranus. Effective temperatures of 57.7 + or - 1.8 K and 58.2 + or - 1.9 K are obtained for Uranus and Neptune, respectively, confirming the large internal heat source in Neptune.

Abstract: Energetic-ion phase-space density profiles are strikingly similar in the inner magnetospheres of earth, Jupiter, and Saturn for ions of first adiabatic invariant near 100 MeV/G and small mirror latitudes. Losses occur inside L approximately equal to 7 for Jupiter and Saturn and inside L approximately equal to 5 at earth. At these L values there exist steep plasma-density gradients at all three planets, associated with the Io plasma torus at Jupiter, the Rhea-Dione-Tethys torus at Saturn, and the plasmasphere at earth. Measurements of ion flux-tube contents at Jupiter and Saturn by the low-energy charged-particle experiment show that these are similar (for O ions at L = 5-9) to those at earth (for protons at L = 2-6). Furthermore, the thermal-ion flux-tube contents from Voyager plasma-science data at Jupiter and Saturn are also very nearly equal, and again similar to those at earth, differing by less than a factor of 3 at the respective L values. The near equality of energetic and thermal ion flux-tube contents at earth, Jupiter, and Saturn suggests the possibility of strong physical analogies in the interaction between plasma and energetic particles at the plasma tori/plasma sheets of Jupiter and Saturn and the plasmasphere of earth.

Abstract: Nineteen speckle interferometric observations of the Pluto system have been used to improve the determination of the orbital elements for Pluto's satellite. Calibration uncertainties appear to be the dominant source of error, but the observation of a partial occultation of the satellite by Pluto has been used to constrain the orbit solution. The orbital period is found to be in excellent agreement with the rotational period of the planet, reinforcing the belief that the system is completely tidally evolved. The orbital radius and period imply a total mass for the system of 6.8 + or - 0.5 x 10 to the -9th solar masses. Density constraints place an upper limit of 3615 + or - 90 km on the diameter of Pluto, while observations of the first mutual events establish a crude lower limit of about 2800 km.

Abstract: This new edition is an unrivalled source of information and images covering the whole of modern astronomy. Its 130 articles written by experts form an absorbing panorama of information arranged by topic. Almost every page of the Atlas is richly illustrated with colour photographs, maps, and detailed diagrams. This reference book commences with a survey of the Sun and the solar system, followed by the stars and the Galaxy, and concludes with the extragalactic universe and cosmology. For this edition there are entirely new sections on the planets Venus, Neptune and Pluto, solar system debris, black holes and collapsed stars, active galaxies, galaxy clusters and cosmology. Many photographs have been replaced by improved images from modern telescopes, including the Hubble Space Telescope. An elaborate 24-page glossary and index has been added to increase the ease with which this sumptuous and lavish encyclopedia can be used for quick reference. There are substantial changes throughout the section on the Solar System. The material on Venus is re-written, to take account of the spectacular Magellan mission. The Mars chapter now includes the Phobos results. In the outer solar system new results on the satellites of Jupiter and Saturn are included, as well as new photographs from the Hubble Space Telescope. There is also a new chapter on planetary climate change. The section on stars and the Galaxy now includes chapters on astrometry and protoplanetary systems, as well as many modifications to the existing texts on evolved stars.

Abstract: Planetary satellites, ranging in size from ring particles to the Galilean moons of Jupiter, constitute a small but diverse compmonent of the solar system. In some respects, the satellite systems of the giant planets can be thought of as miniature solar systems. The chemical and physical properties of these systems can yield clues to the conditions under which they may have formed, and thus can constrain models of the circumplanetary nebulae and the solar nebula. Planetary rings contain a great deal of structure, most strikingly displayed in Voyager spacecraft images. Understanding the causes of this structure can yield important insights into the dynamics of the protoplanetary disk. Taken together, rings and moons offer clues as to the nature of the processes which led to the formation of the planets themselves.

Abstract: The thermal structure and composition of Uranus, Neptune, Saturn, Jupiter, Titan, and Io are described Molecular hydrogen is the dominant constituent in the atmosphere of the outer planets The hydrogen and helium, methane, ammonia and phosphine, and carbon monoxide photochemical reactions of the outer planets are studied The importance of Jupiter's lightning as a source of organic matter is examined The aerosol and haze layers of the stratosphere of Jupiter, Saturn, Neptune, and Uranus are observed The photochemistry of Titan's atmosphere, which includes nitrogen, methane, carbon monoxide, and carbon dioxide reactions, is analyzed The SO2 atmosphere on Io is discussed

Abstract: This new edition is an unrivalled source of information and images covering the whole of modern astronomy. Its 130 articles written by experts form an absorbing panorama of information arranged by topic. Almost every page of the Atlas is richly illustrated with colour photographs, maps, and detailed diagrams. This reference book commences with a survey of the Sun and the solar system, followed by the stars and the Galaxy, and concludes with the extragalactic universe and cosmology. For this edition there are entirely new sections on the planets Venus, Neptune and Pluto, solar system debris, black holes and collapsed stars, active galaxies, galaxy clusters and cosmology. Many photographs have been replaced by improved images from modern telescopes, including the Hubble Space Telescope. An elaborate 24-page glossary and index has been added to increase the ease with which this sumptuous and lavish encyclopedia can be used for quick reference. There are substantial changes throughout the section on the Solar System. The material on Venus is re-written, to take account of the spectacular Magellan mission. The Mars chapter now includes the Phobos results. In the outer solar system new results on the satellites of Jupiter and Saturn are included, as well as new photographs from the Hubble Space Telescope. There is also a new chapter on planetary climate change. The section on stars and the Galaxy now includes chapters on astrometry and protoplanetary systems, as well as many modifications to the existing texts on evolved stars.

Abstract: Power is supplied to a planet's magnetosphere from the kinetic energy of planetary spin and the energy flux of the impinging solar wind. A fraction of this power is available to drive numerous observable phenomena, such as polar auroras and planetary radio emissions. In this report our present understanding of these power transfer mechanisms is applied to Uranus to make specific predictions of the detectability of radio and auroral emissions by the planetary radio astronomy (PRA) and ultraviolet spectrometer (UVS) instruments aboard the Voyager spacecraft before its encounter with Uranus at the end of January 1986. The power available for these two phenomena is (among other factors) a function of the magnetic moment of Uranus. The date of earliest detectability also depends on whether the predominant power source for the magnetosphere is planetary spin or solar wind. The magnetic moment of Uranus is derived for each power source as a function of the date of first detection of radio emissions by the PRA instrument or auroral emissions by the UVS instrument. If we accept the interpretation of ultraviolet observations now available from the Earth-orbiting International Ultraviolet Explorer satellite, Uranus has a surface magnetic field of at least 0.6 gauss, and more probably several gauss, making it the largest or second-largest planetary magnetic field in the solar system.

Abstract: Asteroids that orbit the Sun in a belt between the orbits of Mars and Jupiter are well known. A few other asteroids cross Earth's orbit, and, from time to time, one collides with our planet, as figure 1 so clearly indicates. What are they made of? How did they originate? We suspect that material much like the asteroids played a part in the origin of the solar system—can we see similar forces at work elsewhere?

Abstract: The origin of the outer planets and their satellite systems is discussed within the framework of astrophysical theories of the origin of stars and the nature of viscous accretion disks The nature of the outer planet systems is reviewed, and the gas-instability and core-instability models of the origin of the outer planets are described Critical tests of the models are discussed, showing that the core-instability model is favored The main phases of evolution that the giant planets underwent during and after their formation are outlined, and the source of their current excess luminosity is considered in detail The origin of the regular and irregular satellites of the outer planets is discussed, focusing on their formation in viscous accretion disks or by collision, and the possibility of capture by planets

Abstract: It is shown that the rings of Uranus are mostly immersed in the solar wind if Uranus lacks an intrinsic magnetic field. Except for geologically active moons like Io, the rings and moons of Jupiter and Saturn have either high albedos in a low radiation environment or low albedos in a high radiation environment. It is suggested that the moons of Uranus have a significantly lower albedo than those in the low radiation environment of Saturn, and that the rings of Uranus are black because the rings and moons of that planet are relatively depleted in their surface stores of ices. In this scenario, immersion of the Uranus rings in the solar wind provides a loss mechanism for ring ices. The black rings may thus imply the lack of an intrinsic Uranus magnetic field.

Abstract: The discovery of Quasi-Stellar Objects (QSO’s) and the development of Very Long Baseline Interferometry (VLBI) techniques since the early 1960’s have afforded an extremely precise coordinate grid system or reference frame on the sky. Since the QSO’s are both stellar-like objects and strong emitters of radio flux, their positions can be measured with both optical and radio techniques. However, the radio VLBI measurements on simple, compact sources are by far the most precise, the useful unit being micro-radians. The origin of the VLBI reference frame is tied to the stellar reference frame by the measurements of Hazard et al. (1971) who precisely measured the optical position of the QSO 3C273 with lunar occultations, which, when combined with VLBI position measurements of the same source, ‘‘tied’’ the VLBI and stellar position frames together. Their reported accuracy is ±0.15 arc seconds, but there is good reason to believe that the error in that frame tie is significantly smaller. Radio tracking measurements of spacecraft associated with the inner planets, such as the Viking Orbiters around Mars, combined with VLBI measurements indicate that the frames of the inner planets (i.e. their ephemerides), stellar system, and the VLBI reference sources are consistent to better than ±0:’03 (Newhall et al., 1984).