in the solar system. actually it is not easy to give a clear， rigorous and physically meaningful definition of the stability of our solar system.
among many definitions of stability， here we adopt the hill definition (gladman 1993): actually this is not a definition of stability， but of instability. we define a system as becoming unstable when a close encounter occurs somewhere in the system， starting from a certain initial configuration (chambers， wetherill & boss 1996; ito &