  In about 6 Giga years our Sun will evolve into a red giant and finally end
its life as a white dwarf. This stellar metamorphosis will occur to virtually
all known host stars of exo-planetary systems and is therefore crucial for
their final fate. It is clear that the innermost planets will be engulfed and
evaporated during the giant phase and that planets located farther out will
survive. However, the destiny of planets in-between, at ~ 1 - 10 au, has not
yet been investigated with a multi-planet tidal treatment. We here combine for
the first time multi-planet interactions, stellar evolution, and tidal effects
in an N-body code to study the evolution of a Neptune-Jupiter planetary system.
We report that the fate of the Neptune-mass planet, located closer to the star
than the Jupiter-mass planet, can be very different from the fate of a single
Neptune. The simultaneous effects of gravitational interactions, mass loss and
tides can drive the planetary system towards mean motion resonances. Crossing
these resonances affects particularly the eccentricity of the Neptune and
thereby also its fate, which can be engulfment, collision with the Jupiter-mass
planet, ejection from the system, or survival at a larger separation.
