Secure TTV Mass Measurements: Ten Kepler Exoplanets between 3 and 8 Earth Masses with Diverse Densities and Incident Fluxes

TL;DR

This study uses transit timing variations from Kepler data to measure the masses of ten exoplanets between 3 and 8 Earth masses, revealing diverse densities and compositions, and providing insights into their orbital dynamics and host star parameters.

Contribution

It presents robust dynamical mass measurements for ten Kepler exoplanets, including density estimates and orbital configurations, using comprehensive TTV analysis and improved stellar parameters.

Findings

Ten exoplanets have robust mass measurements.

Diverse densities observed among sub-Neptune planets.

Density inversely correlated with incident flux.

Abstract

We infer dynamical masses in eight multi-planet systems using transit times measured from Kepler's complete dataset, including short-cadence data where available. Of the eighteen dynamical masses that we infer, ten pass multiple tests for robustness. These are in systems; Kepler-26 (KOI-250), Kepler-29 (KOI-738), Kepler-60 (KOI-2086), Kepler-105 (KOI-115), and Kepler-307 (KOI-1576). Kepler-105 c has a density consistent with an Earth-like composition. Strong TTV signals were detected from additional planets, but their inferred masses were sensitive to outliers or consistent solutions could not be found with independently-measured transit times, including planets at; Kepler-49 (KOI-248), Kepler-57 (KOI-1270), Kepler-105 (KOI-115) and Kepler-177 (KOI-523). Strong upper limits on the mass of Kepler-177 c imply an extremely low density ~0.1 g cm$^{-3}$. In most cases, individual orbital eccentricities were poorly constrained due to degeneracies in TTV inversion. For five planet pairs in our sample, strong secular interactions imply a moderate-to-high likelihood of apsidal alignment over a wide range of possible eccentricities. We also find solutions for the three planets known to orbit Kepler-60 in a Laplace-like resonance chain. However, non-librating solutions also match the transit-timing data. For six systems, we calculate more precise stellar parameters than previously known, enabling useful constraints on planetary densities where we have robust mass measurements. Placing these exoplanets on the mass-radius diagram, we find a wide range of densities is observed among sub-Neptune mass planets and that the range in observed densities is anti-correlated with incident flux.