Classification and the Stability of the Isothermal Protoplanetary Equilibria
          Bojan Pecnik, Max-Planck-Institute for extraterrestrial Physics
          Guenther Wuchterl, Astronomical Institute of the Jena University
          The work aims to clarify some basic concepts of the giant planet formation.  In order to enhance the understanding of the general roadmap of the giant planet formation we mapped out all the qualitatively different protoplanetary equilibria, for a simple isothermal self-gravitating core-envelope model.  A clear concept for the distinction between a planet and a minor body naturally follows from our static classification. We explain e.g. why Titan has an atmosphere, while Ganymede has none.  Also, we offer a new interpretation for the locally isothermal disk-planet calculations.  We examine the role of so-called critical mass, necessary to permanently attract gas of the protoplanetary nebula to a terrestrial-planet-like, heavy element core.  To determine the subset of the physically significant protoplanetary solutions, as well as to investigate the role of the stability in the formation of the planets, we perform the non-linear stability analysis - the evolution of the models which are the typical representatives of their class is followed on a timescale of the envelope dynamics.We investigate the possible transitions within the classified protoplanetary solution set, and try to estimate the required envelope perturbations.