  A simple dynamical model is employed to study the possible orbital evolution
of scattered planets and phase plane analysis is used to classify the parameter
space and solutions. Our results reconfirm that there is always an increase in
eccentricity when the planet was scattered to migrate outward when the initial
eccentricity is zero. Applying our study on the Solar System and considering
the existence of the Kuiper Belt, this conclusion implies that Neptune was
dynamically coupled with the Kuiper Belt in the early phase of the Solar
System, which is consistent with the simulational model in Thommes, Duncan &
Levison (1999).
