A super-Earth and a mini-Neptune around Kepler-59

TL;DR

This study characterizes the Kepler-59 planetary system, determining star and planet parameters, and infers planetary masses and orbits using transit timing variations, revealing a stable system with a super-Earth and a mini-Neptune.

Contribution

It introduces a Bayesian inference method combined with N-body simulations to accurately determine planetary masses and orbital parameters from TTV data.

Findings

Inner planet is a super-Earth (~5 M_⊕)

Outer planet is a mini-Neptune (~3 M_⊕)

System is dynamically stable over millions of years

Abstract

We characterize the radii and masses of the star and planets in the Kepler-59 system, as well as their orbital parameters. The star parameters are determined through a standard spectroscopic analysis, resulting in a mass of $1.359\pm 0.155\,M_\odot$ and a radius of $1.367\pm 0.078\,R_\odot$. The planetary radii obtained are $1.5\pm 0.1\,R_\oplus$ for the inner and $2.2\pm 0.1\,R_\oplus$ for the outer planet. The orbital parameters and the planetary masses are determined by the inversion of Transit Timing Variations (TTV) signals. For this, we consider two different data sets, one provided by Holczer et al. 2016, with TTVs only for the planet Kepler-59c, and the other provided by Rowe et al. 2015, with TTVs signals for both planets. The inversion method is carried out by applying an algorithm of Bayesian inference (MultiNest) combined with an efficient N-body integrator (Swift). For each of the data sets, two possible solutions are found, both having the same probability according to their corresponding Bayesian evidences. All four solutions appear to be indistinguishable within their 2-$\sigma$ uncertainties. Nevertheless, statistical analyses show that the solutions from Rowe et al. 2015 data better characterize the data. The first and second solutions identify masses of $5_{-2}^{+4}~M_{\mathrm{\oplus}}$ and $4.6_{-2.0}^{+3.6}~M_{\mathrm{\oplus}}$, and $3.0^{+0.8}_{-0.8}~M_{\mathrm{\oplus}}$ and $2.6^{+1.9}_{-0.8}~M_{\mathrm{\oplus}}$ for the inner and outer planet, respectively. This points to a system with an inner super-Earth and an outer mini-Neptune. Dynamical studies show the planets have almost co-planar orbits with small eccentricities ($e<0.1$), close but not into the 3:2 mean motion resonance. Stability analysis indicates that this configuration is stable over million years of evolution.