Revised Mass and Orbit of ε Eridani b: A 1 M Jup Planet on a Near-circular Orbit

Abstract The mature Jovian planet ε Eridani b ( ε Eri 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 (RV) and astrometry data, combining data from eight RV instruments and four astrometric sources (Hipparcos, the Hubble Space Telescope’s Fine Guidance Sensor, Gaia Data Release 2, and Gaia Data Release 3). We incorporate methodological advances that impact our findings, including a principled treatment of correlation between Gaia DR2 and DR3 velocity. We revise the planet’s mass upward to 1.00 ± 0.10 M J up and find that its orbit is nearly circular and likely to be 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 ε Eri b is one of the closest analogs to a solar system planet yet detected around a nearby star.