On the problem of origin of periodic comets.

The problem of origin of periodic comets is viewed under various aspects. A steady growth of the fraction of these comets in the overall population of comets is emphasized. The number of discovered periodic comets with small eccentricities and the Jacobi constants close to 3 is also growing with time. A comparison of maximum magnitudes of the same comets in different apparitions at the same elongations as well as an analysis of exhausted comets indicates that the age of these objects does not exceed 1000 years. Capture is considered as an efficient mechanism for preserving equilibrium in reasonable time intervals. The analysis of the data given by Everhart and the results of calculations of the evolution of cometary orbits reveal small efficiency of capture. A comparison of the number of well established cases of capture with the corresponding time interval shows that the age of the system of periodic comets must be 17000 years within the framework of this mechanism. This is not unlikely. Secular variations of the distributions of semimajor axes, inclinations, longitudes of perihelia, eccentricities of orbits of periodic comets are analysed. On the average the eccentricities tend to increase, but this conflicts with the capture mechanism. The conclusion is drawn that the concept of capture in its classical and modern versions is unable to solve the problem of the origin of periodic comets as a whole. Other, more effective sources and mechanisms seem to be also in operation in enlarging the cometary system.