Planet-planet Scattering In Exoplanet Systems And Planet Interior

Exoplanets are great discoveries in the last century in the field of astronomy. Compared to the planets in the solar system, exoplanets have many particular properties such as the prevalence of planets on high eccentric orbits; the emergences of hot Jupiters and hot Earthes; mean motion resonances in multi-planet systems; planet structure abnormalities. In2009, the launch of Kepler Space Telescope brought new opportunities for exoplanet researches. With the release of Kepler data, some surprising discoveries have emerged. For example, Kepler first discovered six planets orbiting two main-sequence stars (P-type planets); a large number of small-size planets are found; closely packed planetary systems (e.g. Kepler-11) are observed. In addition, Kepler and other plans are devoting themselves to searching exomoons. Our works are based on these observational backgrounds and include four aspects: planet-planet scattering (PPS) in circumbinary planet systems; the formation of P-type terrestrial planets in habitable zone; the effects of PPS on the survival of exomoons; interior structures of hot Earths.In Chapter1, research backgrounds and previous researches are introduced by mainly focusing on our topics. They are (1) observational characteristics of exoplanets;(2) scattering mechanism and its application in multi-planet systems;(3) P-type planet formation and orbital evolution;(4) exomoons.In Chapter2, we systematically study the PPS in circumbinary binary planetary systems. Fluid simulations have shown that the convergence migration between P-type planets will cause scattering between them. Based on numerical simulations, we explore the PPS in various binary configurations. We found a lot of differences compared to PPS in single star systems. For example, we found the outward migrations of the survived planets, the diversity of eccentricity distribution. We also find the phenomenon that PPS can turn a circumbinary planet into a’S-type’ planet. Based on the configurations of observed P-type planetary systems, we discuss possible applies of our model and predict the future observations. In Chapter3, we study the formation of P-type terrestrial planets. According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, significant amount of small planetesimals must exist in the inner zone when embryos were forming outside this CSMA. So embryos migration induced by the planetesimal swarm is possible after the gas disk depletion. Through numerical simulations, we found (i) the scattering-driven inward migration of embryos is robust, planets can form in the habitable zone if we adopt a mass distribution of MMSN-like disk;(ii) the total mass of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations;(iii) the scattering-driven migration of embryos is a natural water-deliver mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.We study the effects of PPS on the survival of exoplanets in Charter4. Compared to the giant planets in the solar system, exoplanets have many remarkable properties such as the prevalence of giant planets on eccentric orbits and the presence of hot Jupiters. PPS between giant planets is a possible mechanism in interpreting above and other observed properties. If the observed giant planet architectures are indeed the outcomes of PPS, such drastic dynamical process must affect their primordial moon systems. In this Letter, we discuss the effect of the PPS on the survival of their regular moons. From the viewpoint of observations, some preliminary conclusions are drawn from the simulations.1. PPS is a destructive process to the moon systems, single planets on eccentric orbits are not the ideal moon-search targets.2. If hot Jupiters formed through PPS, their original moons have little chance to survive.3. Planets in multiple systems with small eccentricities are more likely holding their primordial moons.4. Compared to the lower-mass planets, the massive ones in multiple systems may not be the preferred moon-search targets if the system underwent a PPS history.The interior structures of hot Earthes are explored in Charter5. Possible bulk compositions of the super-Earth exoplanets, CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate and a non-standard carbon model. Their internal structures are deduced using the suitable equation of state of the materials. The degeneracy problems of their compositions can be partly overcome, based on the fact that all three planets are extremely close to their host stars. By analyzing the numerical results, we conclude:1) The iron core of CoRoT-7b is not more than27%of its total mass within1σ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be compatible with an Earth-like core/mantle mass fraction;2) Kepler-10b is more likely with a Mercury-like composition, its old age implies that its high iron content may be a result of strong solar wind or giant impact;3) the transiting-only super-Earth Kepler-9d is also discussed. Combining its possible composition with the formation theory, we can place some constraints on its mass and bulk composition. In Charter6, we summarize our work and discuss some problems in the future study of exoplanets. With the improvement of the observational accuracy and the diversity of observational methods, exoplanet researches will advance from statistics to specifics, from simpleness to details. The dynamic characteristics of exoplanets provide new opportunities for the development of celestial mechanics. The study of the debris disks can help us understand the formation of planets. The ultimate aim of Kepler is to search extrasolar lives, so it is necessary to study exoplanet atmosphere in detail.