Planetary systems and extraterrestrial life

The paper revies the present status of the problem of the existence of other planetary systems in the Galaxy. Observational data and theoretical results are presented to show that the occurrence of planetary systems is, most probably, not a universal phenomenon. Study of the stability of planetary orbits in the vicinity of double stars indicates that, in general, planetary systems can not survive around them over long periods. Therefore, we should rule out the possibility of the existence of planetary systems similar to our own in the neighborhood of double stars. In the solar neighborhood, at least 60% of the stars are known to be members of double systems. The nature of the dark companions is discussed and it is concluded that they are stellar objects and not planets. Recent work on the absence of a perturbation in the motion of Barnard's star is discussed. Comments are made on the existence of extraterrestrial life in the solar system and around other stars in the Galaxy.