Two Giant Planets Orbiting the K Giant Star η Cet

We present evidence of a new planetary system around the K giant η Cet (HIP 5364, HD 6805, HR 334), based on 124 high-precision optical and infrared radial velocity data, taken at Lick Observatory (Hamilton) and at VLT (CRIRES). The best dynamical fit to the data is consistent with two massive planets (m ₁sini~2.6M _Jup , m ₂sini~3.3M_Jup ) and with periods of P ₁~407 days, P ₂~740 days. To test the η Cet system's stability we perform ~ 10,000 dynamical investigations with maximum time spans of 10⁸ years. We find that in case of moderate eccentricities, the planets can be effectively trapped in an anti-aligned stable 2:1 mean motion resonance (MMR), very close to the separatrix. A larger non-resonant stable region exists in low-eccentricity parameter space, although less probable than the 2:1 MMR region.