Revised Mass and Orbit of $\varepsilon$ Eridani b: A 1 Jupiter-Mass Planet on a Near-Circular Orbit

TL;DR

This study refines the mass and orbit of the nearby exoplanet $ ext{ε}$ Eridani b using combined radial velocity and astrometry data, confirming it as a nearly circular, Jupiter-mass planet similar to a Solar System planet.

Contribution

It provides the first orbit model of an exoplanet solely from absolute astrometry and updates the planet's parameters with methodological improvements.

Findings

Mass revised to 0.98 ± 0.09 Jupiter masses.

Orbit is nearly circular and coplanar with debris disk.

Confirmed orbital period independently.

Abstract

The mature Jovian planet $\varepsilon$ Eridani b orbits one of the closest sun-like stars at a moderate separation of 3.5 AU, presenting one of the best opportunities to image a true analog to a solar system planet. We perform a thorough joint reanalysis and cross-validation of all available archival radial velocity and astrometry data, combining data from eight radial velocity instruments and four astrometric sources (Hipparcos, Hubble FGS, Gaia DR2, and Gaia DR3). We incorporate methodological advances that impact our findings including a principled treatment of correlation between Gaia DR2 and DR3 velocity and corrections for the changing light-travel time to this high proper motion system. We revise the planet's mass upward to $0.98 \pm 0.09 \, \mathrm{M_{jup}}$ and find that its orbit is nearly circular and close to coplanar with the outer debris disk. We further present one of the first models of an exoplanet orbit exclusively from absolute astrometry and independently confirm the planet's orbital period. We make specific predictions for the planet's location at key imaging epochs from past and future observing campaigns. We discuss and resolve tensions between previous works regarding the eccentricity, inclination, and mass. Our results further support that $\varepsilon$ Eridani b is one of the closest analogs to a Solar System planet yet detected around a nearby star.