In May 2012, Prof. Ji Jianghui and his PhD student Dong Yao of Purple Mountain Observatory gave some new results of the tidal evolution of two single-planet systems, that is, WASP-50 and GJ 1214 and a two-planet system CoRoT-7 using numerical simulations in one paper published in Science China Physics, Mechanics and Astronomy. The results show that tidal decay and circularization may play a significant role in shaping their final orbits, which is related to the initial orbital data in the simulations.

For WASP-50 system, tidal effect raised by its host star probably make the hot Jupiter WASP-50b arrive at its current circular orbit. For GJ 1214 system, different cases of initial eccentricity are also considered as only an upper limit of its eccentricity (0.27) is shown, and the outcome suggests a possible maximum initial eccentricity (0.4) in the adopted dynamical model. Moreover, additional runs with alternative values of dissipation factor Q’1 are carried out to explore tidal evolution for GJ 1214b, and these results further indicate that the real Q’1 of GJ 1214b may be much larger than its typical value, which may reasonably suggest that GJ 1214b bears a present-day larger eccentricity, undergoing tidal circularization at a slow rate. For CoRoT-7 system, tidal forces make two planets migrating towards their host star as well as producing tidal circularization, and in this process tidal effects and mutual gravitational interactions are coupled with each other. Various scenarios of the initial eccentricity of the outer planet have also been done to investigate final planetary configuration.

Tidal decay arising from stellar tides may still work for each system as the eccentricity decreases to zero, and this is in association with the remaining lifetime of each planet used to predict its future.

This research issignificant to understand how some close-in exo-planets experience the tidal interaction raised by its host star in single-planet systems and the coupled interaction between tides and gravitation in multiple-planet systems, also helpful to explore the formation and evolution of the observed close-in exo-planets currently. The study has been adopted by SCIENCE CHINA Physics Mechanics & Astronomy 2012,Vol.55 No.5 pp.872-879.The published paper is linked by the webpage http://www.springerlink.com/content/c333382g31h09161/.