  The chaotic behaviour of the motion of the planets in our Solar System is
well established. In this work to model a hypothetical extrasolar planetary
system our Solar System was modified in such a way that we replaced the Earth
by a more massive planet and let the other planets and all the orbital elements
unchanged. The major result of former numerical experiments with a modified
Solar System was the appearance of a chaotic window at $\kappa_E \in (4,6)$,
where the dynamical state of the system was highly chaotic and even the body
with the smallest mass escaped in some cases. On the contrary for very large
values of the mass of the Earth, even greater than that of Jupiter regular
dynamical behaviour was observed. In this paper the investigations are extended
to the complete Solar System and showed, that this chaotic window does still
exist. Tests in different 'Solar Systems' clarified that including only Jupiter
and Saturn with their actual masses together with a more 'massive' Earth ($4 <
\kappa_E < 6$) perturbs the orbit of Mars so that it can even be ejected from
the system. Using the results of the Laplace-Lagrange secular theory we found
secular resonances acting between the motions of the nodes of Mars, Jupiter and
Saturn. These secular resonances give rise to strong chaos, which is the cause
of the appearance of the instability window.
