HD 28185 revisited: an outer planet, instead of a brown dwarf, on a Saturn-like orbit

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 MJ 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+0.06 −0.07 d 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 MJ, we reclassify this companion as a super-Jovian planet. HD 28185 c has an orbital period of 24.9+1.3 −1.1 yr, a semimajor axis of 8.50+0.29 −0.26 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 ≈10 au separations is becoming increasingly routine.