  We have studied planetary systems which are similar to the Solar System and
built up from three inner rocky planets (Venus, Earth, Mars) and two outer gas
giants. The stability of the orbits of the inner planets is discussed in the
cases of different masses of the gas planets. To demonstrate the results
stability maps were made and it was found that Jupiter could be four times and
Saturn could be three times more massive while the orbits of the inner planets
stay stable. Similar calculations were made by changing the mass of the Sun. In
this case the position of the rocky planets and the extension of the liquid
water habitable and the UV habitable zones were studied for different masses of
the Sun. It was found that the orbits of the planets were stable for values
greater than 0.33 M_Sun where M_Sun is the mass of the Sun and at lower masses
of the Sun (at about 0.8 M_Sun) only Venus, but for higher mass values (at
about 1.2 M_Sun) Earth and also Mars are located in both habitable zones.
