2019MNRAS.483.1970B

We report the discovery of K2-161b, which was first identified as a planetary candidate from Kepler K2 photometry of Campaign 14, and whose planetary nature and orbital parameters were then confirmed with precision radial velocities. K2-161b is half as massive as Saturn ( M_P= 0.179 ±0.021 M_J), and has a radius of R_P= 0.840 ±0.011 R_J, which translates into a bulk density of ρ_P=0.37 ±0.05 g cm^–3. K2-161b transits its slightly evolved G-type host star ( M_*= 1.105 ±0.019 M_☉, R_*= 1.669 ±0.022 R_☉) every 11.633 64 ± 0.000 10 d and presents a significantly eccentric orbit (e = 0.420 ± 0.034). We estimate a relatively short circularization time-scale of 1.8 Gyr for the planet, but given the advanced age of the system we expect the planet to be engulfed by its evolving host star in ∼1 Gyr before the orbit circularizes. The low density of the planet coupled to the brightness of the host star (J = 9.4) makes this system one of the best candidates known to date in the super-Neptune regime for atmospheric characterization via transmission spectroscopy, and to further study the transition region between ice and gas giant planets.