Showing papers on "Planetary system published in 1977"

Dynamic Relaxation of Planetary Systems and Bode's Law

Abstract: BODE'S law, which states that the semi-major axis ri of the ith planet from the Sun is given by where a is a constant, is obeyed by the inner satellites of Jupiter, Saturn and Uranus as well as the planets1. Because the initial conditions in these satellite systems are not likely to have been the same as in the planetary system, this suggests to me that Bode's law may have resulted from a process of dynamical relaxation. That an epoch characterized by strong dynamical encounters occurred before the planets relaxed into stable orbits is also suggested by the surprisingly large differences between the inclinations of their angular momentum vectors of rotation and those of orbital revolution.

Thermal evolution of planetary size bodies

Abstract: The size dependence of planetary thermal evolution is investigated through calculations which take into account the effects of heat source differentiation and convection. The theoretical computations make use of hypothetical bodies for minor planets; Mercury, Venus and Mars are employed to represent the size spectrum of the inner planets. If started at a cold initial condition, an object with a radius less than 1000 km is unlikely to reach melting. Accretional heating, inductive heating and short half-life radioactive heating are among the mechanisms which may produce early melting and differentiation in larger planets. Core formation in Mercury and Venus is also discussed.

Time scale for the formation of the earth and planets and its role in their geochemical evolution

Abstract: The initial mass of the solar nebula is discussed. Models of a massive nebula (two solar masses and more) encounter serious difficulties: an effective mechanism of transfer of the momentum from the central part of the nebula outward, capable of leading to formation of the sun and removal of half the mass of the nebula from the solar system has not been found. As a consequence of the instability of these models, their evolution can end with the formation, not a planetary system, but of a binary star. The possibility is demonstrated of obtaining acceptable growth rates for Uranus and Neptune by prolonging the thickening of preplanetary dust in the region of large masses. The important role of large bodies in the process of formation of the planets is noted. The impacts of such bodies, moving in heliocentric orbits, could have imparted considerable additional energy to the forming Moon, which, together with the energy given off by the joining of a small number of large protomoons, could have led to a high initial temperature of the moon.

The companions of sunlike stars.

Abstract: An investigation was conducted in which the spectra of 123 comparatively bright stars were studied to learn about companion stars or planets. Extrapolation of the data presented suggests that all of the 123 primary stars in the sample have companions: 67 percent of the secondaries are normal stars, 15 percent are black dwarfs, and 20 percent are planets. 5 figs. (GHT)

Infrared Observations of the Planets

Abstract: Although infrared detectors were first trained on the planets many years ago, recent dramatic improvements in the sensitivity and sophistication of the instruments is resulting in surprising and fundamental discoveries. The inner planets and their satellites are in the process of a thorough exploration by spacecraft. However, it is the outer planets-so foreign from the earth—that hold the greatest fascination for many of us, and study of the infrared emission of these objects still depends largely on earthbased telescopes. Infrared observations are currently having a fundamental impact in a number of areas of outer solar system research. Four of these areas are discussed below—the nature of comets, the structure of the atmospheres of the outer planets, the surfaces of small bodies in the outer solar system, and the contraction history of the outer planets.

Planetary Systems and Stellar Multiplicity

Abstract: In this paper we have discussed the origin of planetary systems on one hand and binary and multiple stars on the other. First we show that phenomenological differences between these two kinds of celestial objects are due to their genetic difference. The basic point is that formation of a planetary system around a star has to be a minor event in the life history of the star while formation of a binary or multiple system has to be an event that is important equally to all components of the system. Thus the planetary system evolves from a rotating disk of gaseous and dust particles that comes into being after the star has already been there. It is therefore reasonable to suggest that the rotating disk results from transfer of angular momentum from the central star to the surrounding medium which is likely a residue left over in the process of formation of the central star. Binary and multiple systems cannot be formed in this way because they do not show the characteristics of having come out of a rotating disk. The dominant mechanism of their formation is that they were formed naturally as they are, each from perhaps a single condensation in the interstellar medium. However such a single mechanism of formation cannot satisfactorily explain the observed spread of binaries in mean separations between two components (or equivalently orbital periods). But the disagreement may be removed by including a small number of binaries formed by other processes and by considering the change of orbital elements of binaries after their formation. Trapezia were likely formed also by more than one mechanism. That several stars could be formed, from a single condensation requires the” existence oi pre-stellar nuclei which are briefly: discussed at the end of the paper.