Dynamical properties of the multiplanet system around HD 169830

A new extrasolar system consisting of two planets orbiting HD 169830 has been discovered by the Geneva Extrasolar Planet Search team. We study its orbital dynamics in the framework of the N-body problem. The analysis of the orbital stability is performed using long-term integrations and fast indicators, the mean exponential growth factor of nearby orbits, and a modified Fourier transform. The HD 169830 system 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 the low-order mean motion resonances, 9:1 and 10:1. The long-term integration of the coplanar configurations, conducted over 1 Gyr, reveals that the eccentricities of the companions reach large values, similar or equal to0.4-0.5, but there is no sign of instability. Highly inclined configurations appear to be stable as well. The planetary system around HD 169830 belongs to the class of hierarchical planetary systems. In particular, the orbital parameters of the planets around HD 169830 resemble those of another two-planet system, around HD 12661. We investigate whether these two planetary systems are dynamically similar.