K2-161b: a low-density super-Neptune on an eccentric orbit
Jones, M. I.; Cortés, C.; Rabus, M.; Espinoza, N.; Drass, H.; Henning, Th; Jordán, A.; Soto, M. G.; Jenkins, J. S.; Díaz, M. R.; Sarkis, P.; Brahm, R.; Pantoja, B.; Vučković, M.; Rojas, F.; Zapata, A.; Lachaume, R.; Vasquez, S.
Chile, Germany
Abstract
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 MJ), 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_{\star }= 1.105 ± 0.019 M_{⊙ }, R_{\star }= 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.