the division of astrophysics that deals with studies of the physical structure and chemical composition of the planets and their satellites. Before the advent of direct studies of the planets by means of space probes, all information on the structure and composition of the planets was obtained by astronomical methods. For example, the masses of the planets and the mass distribution within a planet were determined by studying regularities of the motion of the planets and their satellites, while the chemical composition of a planetary atmosphere was determined from the spectrum of solar radiation reflected by the planet. In addition, a planet’s temperature was determined from the infrared and radio-frequency radiation of the planet, and cloud-layer characteristics and surface microstructure were determined from the polarization of scattered solar radiation. Beginning in the 1960’s, the classical astronomical methods of planetary research have been supplemented by the wide use of direct measurements made by space probes in the atmosphere, on the surface, or in the immediate vicinity of a planet.
As a rule, the methods of direct studies are a development of geophysical techniques. On the other hand, the evolution of space technology made it possible to use astronomical methods to study the earth. Since the mid-1970’s, the field of science that deals with the comprehensive study of the planets and satellites by various methods has been called planetology.
G. A. LEIKIN