  The three-planet extrasolar system of HD 181433 has been detected with HARPS.
The best-fit solution, announced by the discovery team, describes a highly
unstable, self-disrupting configuration. In fact, a narrow observational
window, only partially covering the longest orbital period, can lead to
solutions representing unrealistic scenarios. Taking into account the dynamical
stability as an additional observable while interpreting the RV data, we can
analyse the phase space in a neighbourhood of the statistically best-fit and
derive dynamically stable configurations that reproduce the observed RV signal.
Our Newtonian stable best-fit model is capable of surviving for at least 250
Myrs. The two giant companions are found to be locked in the 5:2 MMR as Jupiter
and Saturn in the Solar System. This mechanism does not allow close encounters
even in case of highly eccentric orbits. Moreover, planets c and d are located
in regions spanned by many other strong low-order MMRs. We study the dynamics
of some plausible scenarios and we illustrate the behaviours caused by secular
apsidal resonances and mean motion resonances. Furthermore, we find a
terrestrial planet in the habitable zone of HD 181433 can retain stability.
Apart from filling an empty gap in the system, this body could offer a harbour
for life indeed. Additional measurements are necessary in order to investigate
this hypothesis and can confirm the predictions outlined in the paper.
