Kepler-167e as a Probe of the Formation Histories of Cold Giants with Inner Super-Earths

TL;DR

This study investigates Kepler-167, a unique planetary system with inner super-Earths and an outer Jupiter-like planet, using observations and models to understand its formation within the pebble accretion framework.

Contribution

It provides new mass and composition measurements of Kepler-167e and explores how such systems form in massive, metal-rich protoplanetary disks.

Findings

Kepler-167e has a mass of about 1 Jupiter mass and is metal-enriched.

The protoplanetary disk likely contained over 300 Earth masses of dust.

Disk models suggest a large, massive disk consistent with observed giant planet occurrence.

Abstract

The observed correlation between outer giant planets and inner super-Earths is emerging as an important constraint on planet formation theories. In this study we focus on Kepler-167, which is currently the only system known to contain both inner transiting super-Earths and a confirmed outer transiting gas giant companion beyond 1 au. Using long term radial velocity monitoring, we measure the mass of the gas giant Kepler-167e ($P=1071$ days) to be $1.01^{+0.16}_{-0.15}$ M$_{\rm J}$, thus confirming it as a Jupiter analog. We re-fit the $Kepler$ photometry to obtain updated radii for all four planets. Using a planetary structure model, we estimate that Kepler-167e contains $66\pm19$ M$_{\oplus}$ of solids and is significantly enriched in metals relative to its solar-metallicity host star. We use these new constraints to explore the broader question of how systems like Kepler-167 form in the pebble accretion framework for giant planet core formation. We utilize simple disk evolution models to demonstrate that more massive and metal-rich disks, which are the most favorable sites for giant planet formation, can also deliver enough solids to the inner disk to form systems of super-Earths. We use these same models to constrain the nature of Kepler-167's protoplanetary disk, and find that it likely contained $\gtrsim 300$ M$_{\oplus}$ of dust and was $\gtrsim 40$ au in size. These values overlap with the upper end of the observed dust mass and size distributions of Class 0 and I disks, and are also consistent with the observed occurrence rate of Jupiter analogs around sun-like stars.