The exosystems about HD169830 and HD12661: are they dynamical twins?

The orbital parameters of a new 2-planetary system HD 169830 have been announced during the XIX-th IAP Colloquium "Extrasolar Planets: Today & Tomorrow", (Paris, June 30 - July 4, 2003) by the Geneva Extrasolar Planet Search Team. We study the global dynamics of this system in the framework of the $N$-body problem. The preliminary analysis of its orbital stability presented in this paper is performed using the long-term integrations and the fast indicators, the Mean Exponential Growth factor of Nearby Orbits and the Frequency Map Analysis. The HD 169830 appears to be located in a wide stable region of the phase space. The ratio of the mean motions of the planets HD 169830 b and c is between two low-order mean motion resonances, 6:1 and 7:1. The long-term integration of the coplanar configurations, conducted over 1Gyr, reveals that the eccentricities of the companions vary with a large amplitude $\simeq 0.3$ but there is no sign of instability. An important factor for maintaining the orbital stability is the presence of the apsidal secular resonance with the apsides on the average antialigned. This resonance persists over a wide range of the initial conditions and is characterized by a large semi-amplitude of the librations $\simeq 90^{\circ}$. Curiously, the orbital parameters and the qualitative picture of this system closely resemble those of another 2-planetary system, around HD 12661. Both of them can be classified as hierarchical planetary systems. Possibly, there exists another one with a very similar configuration, the planetary system around HD 160691. The dynamical similarity of these exosystems raises a question whether their formation and subsequent orbital evolution obeys a common rule and whether they could be members of a specific class of the extrasolar planetary systems.