EPIC 201498078b: A low density Super Neptune on an eccentric orbit

TL;DR

This paper reports the discovery and characterization of EPIC 201498078b, a low-density super-Neptune with an eccentric orbit, providing insights into its physical properties, orbital dynamics, and potential for atmospheric studies.

Contribution

First detailed characterization of EPIC 201498078b, a super-Neptune with a highly eccentric orbit, including its physical parameters and implications for planetary evolution.

Findings

EPIC 201498078b has a mass of 0.179 M_J and a radius of 0.84 R_J.

The planet exhibits a significant eccentricity of 0.42.

The system is a prime candidate for atmospheric transmission spectroscopy.

Abstract

We report the discovery of EPIC 201498078b, 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. EPIC 201498078b 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$=$0.37 \pm 0.05$ g cm$^{-3}$. EPIC 201498078b transits its slightly evolved G-type host star ($\rm M_{\star}$=$1.105 \pm 0.019$ $\rm M_{\odot}$, $\rm R_P$=$1.669 \pm 0.022$ $\rm R_{\odot}$) every $11.63364 \pm 0.00010$ days and presents a significantly eccentric orbit ($e=0.420 \pm 0.034$). We estimate a relatively short circularization timescale 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 $\sim 1$ 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.