The Anglo-Australian Planet Search. XXV. A Candidate Massive Saturn Analog Orbiting HD 30177

We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analog (HD 30177b: a = 3.8 0.1 au, m sin i = 9.7 0.5 MJup). HD 30177c can be regarded as a massive Saturn analog in this system, with a = 9.9 1.0 au and m sin i = 7.6 3.1 MJup. The formal best-fit solution slightly favors a closer-in planet at a ∼ 7 au, but detailed n-body dynamical simulations show that configuration to be unstable. A shallow local minimum of longer period, lower eccentricity solutions was found to be dynamically stable, and hence we adopt the longer period in this work. The proposed ∼32 year orbit remains incomplete; further monitoring of this and other stars is necessary to reveal the population of distant gas giant planets with orbital separations a ∼ 10 au, analogous to that of Saturn.