  We have performed simulations to investigate the dynamics of the M dwarf star
GJ 876 in an attempt to reveal any stabilizing mechanism for sustaining the
system.We simulated different coplanar and noncoplanar configurations of
two-planet systems and other cases.From the simulations,we found that the 2 :1
mean-motion resonance between two planets can act as an effective mechanism for
maintaining the stability of the system.This result is explained by a proposed
analytical model.Using this model,we studied the region of motion of the inner
planet by varying the parameters of the system,and we detected that the
analytical results are well consistent with the numerical simulations.
