Detection and characterization of an ultra-dense sub-Neptunian planet orbiting the Sun-like star K2-292

We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. The planet K2-292 b is a warm sub-Neptune on a 17 day orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of M-* = 1.00 +/- 0.03 M-circle dot and R-* = 1.09 +/- 0.03 R-circle dot , respectively. We modeled simultaneously the K2 photometry and CARMENES spectroscopic data and derived a radius of R-p = 2.63(-0.10)(+0.12)R(circle plus) and mass of M-p = 24.5(-4.4)(+4.4)M(circle plus), yielding a mean density of rho(p) = 7.4(-1.5)(+1.6)g cm(-3) , which makes it one of the densest sub-Neptunian planets known to date. We also detected a linear trend in the radial velocities of K2-292 (gamma(RV) = -0.40(-0.07)(+0.07) m s(-1) d(-1)) that suggests a long-period companion with a minimum mass on the order of 33 M-circle plus. If confirmed, it would support a formation scenario of K2-292 b by migration caused by Kozai-Lidov oscillations.