We have constructed a mapping for the planar circular restricted three-body
problem and used it to study the structure and stability of the phase spac
e near the Lagrangian triangular points of libration. It is found that when
the mass ratio of the primaries mu < 0.02165, and excepting the value mu =
0.01441, the libration point is surrounded by invariant curves, hence is s
table. This is in agreement with theoretical result and demonstrates the ef
fectiveness of the mapping method.