Giant Outer Transiting Exoplanet Mass (GOT 'EM) Survey. II. Discovery of a Failed Hot Jupiter on a 2.7 Year, Highly Eccentric Orbit

TL;DR

This paper reports the discovery of Kepler-1704 b, a highly eccentric, transiting giant exoplanet on a long orbit, providing insights into high eccentricity migration and potential for atmospheric studies with JWST.

Contribution

It presents the first detailed characterization of a failed hot Jupiter with extreme eccentricity, expanding understanding of giant planet migration and orbital evolution.

Findings

Kepler-1704 b has an eccentricity of 0.921 and a 988.88-day orbit.

The planet's orbit spans 0.16 to 3.9 au, with a temperature variation over 700 K.

It is a promising target for atmospheric characterization with JWST.

Abstract

Radial velocity (RV) surveys have discovered giant exoplanets on au-scale orbits with a broad distribution of eccentricities. Those with the most eccentric orbits are valuable laboratories for testing theories of high eccentricity migration. However, few such exoplanets transit their host stars thus removing the ability to apply constraints on formation from their bulk internal compositions. We report the discovery of Kepler-1704 b, a transiting 4.15 $M_{\rm J}$ giant planet on a 988.88 day orbit with the extreme eccentricity of $0.921^{+0.010}_{-0.015}$. Our decade-long RV baseline from the Keck I telescope allows us to measure the orbit and bulk heavy element composition of Kepler-1704 b and place limits on the existence of undiscovered companions. Kepler-1704 b is a failed hot Jupiter that was likely excited to high eccentricity by scattering events that possibly began during its gas accretion phase. Its final periastron distance was too large to allow for tidal circularization, so now it orbits it host from distances spanning 0.16 - 3.9 au. The maximum difference in planetary equilibrium temperature resulting from this elongated orbit is over 700 K. A simulation of the thermal phase curve of Kepler-1704 b during periastron passage demonstrates that it is a remarkable target for atmospheric characterization from the James Webb Space Telescope, which could potentially also measure the planet's rotational period as the hot spot from periastron rotates in and out of view. Continued characterization of the Kepler-1704 system promises to refine theories explaining the formation of hot Jupiters and cool giant planets like those in the solar system.