HD 28185 Revisited: an Outer Planet, Instead of a Brown Dwarf, on a Saturn-Like Orbit

As exoplanet surveys reach ever-higher sensitivities and durations, planets analogous to the Solar system giant planets are increasingly within reach. HD 28185 is a Sun-like star known to host a m sin i = 6 M-J planet on an Earth-like orbit; more recently, a brown dwarf with a more distant orbit has been claimed. In this work, we present a comprehensive re-analysis of the HD 28185 system, based on 22 yr of radial velocity (RV) observations and precision Hipparcos-Gaia astrometry. We confirm the previous characterization of HD 28185 b as a temperate giant planet, with its 385.92(-0.07d)(+0.06) orbital period giving it an Earth-like incident flux. In contrast, we substantially revise the parameters of HD 28185 c; with a new mass of m =6.0 +/- 0.6 M-J, we reclassify this companion as a super-Jovian planet. HD 28185 c has an orbital period of 24.9(-1.1)(+1.3)yr, a semimajor axis of 8.50(-0.26)(+0.29) au, and a modest eccentricity of 0.15 +/- 0.04, resulting in one of the most Saturn-like orbits of any known exoplanet. HD 28185 c lies at the current intersection of detection limits for RVs and direct imaging, and highlights how the discovery of giant planets at approximate to 10 au separations is becoming increasingly routine.