Key Roles Of Gas Disc On The Formation And Evolution Of Planetary Systems

The detection of exoplanets becomes hotter and hotter, especially the detection of Earth-like planets in habitable zone. As the accumulation of observed datas and progressing of Kepler mission of NASA, more exoplanets can be found or confirmed. The understanding of formation and evolution of exoplanets will be largely improved while much more samples are provided.According to the popular theory of planet formation, protoplanet formed in the protoplanetary disc. Due to the interaction between disc and protoplanets, the prop-erties of the disc play a key role during the formation and evolution of planets. We investigate the later stage of planet formation, when Mars-sized cores appear. Inter-actions among planetary cores can excite their orbital eccentricities, accelerate their mergings and thus sculpture their final orbital architecture. The interaction between cores and gas disc lead to typeâ… orâ…¡migration as well as the eccentricity damping. However the rate of typeâ… migration is still uncertain in different discs models.In Chapiter 1, we introduce the pop methods of exoplanet detection as well as the updating fruits after the launch of Kepler space telescope. We also list some examples of exoplanetary system to show their diversity. Popular planet formation theories, in-cluding gravitational instability and core accretion scenario, are presented in details in Chapter 2.The studies in Chapiter 3 and 4 contribute to the final assembling of planetary systems with N-body simulations, including the typeâ… orâ…¡migration, eccentricity damping of planets and gas accretion of massive cores in viscous discs. To compare with observations in statistics, we use the Monte Carlo method, setting a distribution of different discs. Our results of simulations interpret the distribution of exoplanets from observations and may guide the further observations.In Chapiter 5, considering the uncertainty of the rate or even direction of typeâ… migration, we assume a one dimensional gas disc model, including a density wave due to some perturbation, to survey the migration of low mass planets. The total tidal torques on the planets depend on their phase angle. Adding the propagation of density wave and the eccentric orbit of planet, we find an outward migration criterion for a planet in certain conditions.After the formation of a gas giant, the tidal torque lead to a gap-opening in the disc around the giant. Chapiter 6 provides a one dimensional, quasi-steady, self-gravitational disc model. In this model, there is a positive correlation between the gap width and the surface density of gas disc. Comparing to non-self-gravitational disc model, we find a critical surface density below which the gap width in self-gravitational disc model become narrower than that in non-self-gravitational disc model. Finally in Chapiter 7, we summarize our results and make some discussions.