K2-161b: a low-density super-Neptune on an eccentric orbit. Issue 2 (29th November 2018) - Brahm, R
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 (${\rm M_P}= 0.179 \pm 0.021 \, {\rm M_{J}}$ ), and has a radius of ${\rm R_P}= 0.840 \pm 0.011 \, {\rm R_J}$, which translates into a bulk density of ${\rm \rho _P}=0.37 \pm 0.05 \, \mathrm{g}\, \mathrm{cm}^{-3}$ . K2-161b transits its slightly evolved G-type host star (${\rm M}_{\star }= 1.105 \pm 0.019 \, {\rm M}_{\odot }$, ${\rm R}_{\star }= 1.669 \pm 0.022 \, {\rm R}_{\odot }$ ) 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.