HD 83443c: A Highly Eccentric Giant Planet on a 22 yr Orbit

We report the discovery of a highly eccentric long-period Jovian planet orbiting the hot-Jupiter host HD 83443. By combining radial velocity data from four instruments (AAT/UCLES, Keck/HIRES, HARPS, Minerva-Australis) spanning more than two decades, we find evidence for a planet with m sin i = 1.35(-0.06)(+0.07) M-J, moving on an orbit with a = 8.0 +/- 0.8 au and eccentricity e = 0.76 +/- 0.05. We combine our radial velocity analysis with Gaia eDR3/Hipparcos proper motion anomalies and derive a dynamical mass of 1.5(-0.2)(+0.5)M(Jup). We perform a detailed dynamical simulation that reveals locations of stability within the system that may harbor additional planets, including stable regions within the habitable zone of the host star. HD 83443 is a rare example of a system hosting a hot Jupiter and an exterior planetary companion. The high eccentricity of HD 83443c suggests that a scattering event may have sent the hot Jupiter to its close orbit while leaving the outer planet on a wide and eccentric path.