  The planetary restricted three-body problem (RTBP) is considered. The primary
mass M is much more than another masses mj, i=1..N, which revolve around M. The
massless probe particle m moves on elliptic orbit, is perturbed by mj. It is
well known, that equations of motion of restricted 3-body problem in rotating
rectangular frame may be reduced to the second order differential equation with
periodic coefficients (Hill equation). It gives the ability to estimate width
and position of the unstable zones. Moreover, the dependence of the position of
instable zones from orbital eccentricity of the probe particle is derived. It
is evident, that overlapping of instability zones in strongly perturbed system
can be a source of the chaotic behaviour. The main result of this work may be
formulated in such form: There are not exist stable orbits with e=0 and i=0 in
neighborhood of mean motion resonances (2n-1)/(2n+1). Positions and width of
unstable zones depends from eccentricity. At high order of resonance, instable
zones are overlapped. This fact can explain chaotic nature of according orbits.
