Regularity of Extrasolar Planetary Systems and the Role of the Star Metallicity in the Formation of Planets (Review)

The discovery in 1995 of the first extrasolar giant planet 51 Peg b initiated the physics of extrasolar planetary systems. By May 2004, the total number of the detected planets orbiting other stars was 122, including 24 hot jupiters, which have a semimajor axis of the orbit of less than 0.15 AU. Due to the high activity of researchers who work with the radial-velocity method, the probable candidates, say, in the 75-parsec radius, are quickly exhausted. The OGLE-type objects, even if their number increases, may only slightly contribute to the physics of extrasolar planets (or exoplanets), because even to determine the type of the companion (a giant planet, brown dwarf, or star of small mass) is extremely problematic for such weak objects. A search for Earth-like planets is still far beyond the technical capabilities: the Keplerian velocity of the Sun induced by the Earth is only 0.09 m/s, which requires to improve the results obtained by a factor of 20–30. Particularly important results were obtained in the observations of transits of the object HD 209458b, which became the only object of this type namely due to transits. The hope of finding another short-period object with similar transits is becoming less and less. The important role of the star metallicity in the formation of planetary systems predicted during the first years after the discovery of exoplanets has gained recognition and been developed successfully. Metallicity has become an indicator of the possible presence of planetary systems and, probably, even determines the type of planets. This review also considers the statistical data on the orbital and mass characteristics of exoplanets.