* Astronomy

Title: The Anglo-Australian Planet Search XXV: A Candidate Massive Saturn Analogue Orbiting HD 30177
Author: Robert A. Wittenmyer, Jonathan Horner, M.W. Mengel, R.P. Butler, D.J. Wright, C.G. Tinney, B.D. Carter, H.R.A. Jones, G. Anglada-Escude, J. Bailey, Simon J. O'Toole

We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analogue (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 analogue 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 favours 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.

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