The formation of the present configuration of three hot super-Earths in the planet system HD 40307 is a challenge to dynamical astronomers.With the two successive period ratios both near and slightly larger than 2,the system may have evolved from pairwise2:1 mean motion resonances(MMRs).In this paper,we investigate the evolutions of the period ratios of the three planets after the primordial gas disk was depleted.Three routines are found to probably result in the current configuration under tidal dissipation with the center star,they are:(i)through apsidal alignment only;(ii)out of pairwise 2:1 MMRs,then through apsidal alignment;(iii)out of the 4:2:1 Laplace Resonance(LR),then through apsidal alignment.All the three scenarios require the initial eccentricities of planets～0.15,which implies a planetary scattering history during and after the gas disk was depleted.All the three routines will go through the apsidal alignment phase,and enter a state with near-zero eccentricities finally.We also find some special characteristics for each routine.If the system went through pairwise 2:1 MMRs at the beginning,the MMR of the outer two planets would be broken first to reach the current state.As for routine(iii),the planets would be out of the LR at the place where some high-order resonances are located.At the high-order resonances 17:8 or 32:15 of the planets c and d,the system will possibly enter the current state as the final equilibrium.
With the increasing number of detected exoplanet samples, the statistical properties of planetary systems have become much clearer. In this review, we sum- marize the major statistical results that have been revealed mainly by radial velocity and transiting observations, and try to interpret them within the scope of the classical core-accretion scenario of planet formation, especially in the formation of different orbital architectures for planetary systems around main sequence stars. Based on the different possible formation routes for different planet systems, we tentatively classify them into three major catalogs： hot Jupiter systems, standard systems and distant giant planet systems. The standard systems can be further categorized into three sub-types under different circumstances： solar-like systems, hot Super-Earth systems, and sub- giant planet systems. We also review the theory of planet detection and formation in binary systems as well as planets in star clusters.
Ji-Lin Zhou Ji-Wei Xie Hui-Gen Liu Hui Zhang Yi-Sui Sun
Possible bulk compositions of the super-Earth exoplanets CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate model and a non-standard carbon model. Their internal structures are deduced using a suitable equation of state for the materials. The degeneracy problems of their compo- sitions 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 than 27% of its total mass within lc~ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be com- patible with an Earth-like core/mantle mass fraction; 2） Kepler-10b is more likely to have a Mercury-like composition, with its old age implying 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.
