Worlds Next Door. III. Indirect Evidence for Enhanced Atmospheric Metallicity and/or the Presence of Water Clouds in the Nearest Jupiter-analog <i>ϵ</i>  Eri b

Abstract We present the most sensitive direct imaging search for the nearest ( d = 3.2 pc) Jupiter-analog exoplanet, ϵ Eri b, with JWST/NIRCam coronagraphy between 4 and 5 μ m (F444W). We achieve a 5 σ contrast sensitivity ≈3.0 × 10 −7 (Δ ≈ 16.3 mag) in the F444W filter at the expected planet separation of ≈1″. This is the deepest 4–5 μ m contrast performance achieved for any JWST/NIRCam observation to date at these separations (and &gt;10× better than ground-based limits). Yet, the planet remains elusive to imaging. We update the star’s age to 1.1 ± 0.1 Gyr, older than previous age estimates, using the latest gyrochronology relations. This significantly impacts ϵ Eri b’s inferred effective temperature ( T eff ), which is now expected to lie between 150 and 200 K based on evolutionary models for a 1 M Jup planet. Using cloud-free Sonora Flame Skimmer models and custom PICASO patchy cloud models in the above T eff range, we find that the F444W nondetection of ϵ Eri b can be explained by a metal-enriched atmosphere and/or an atmosphere containing water ice clouds. Both possibilities suggest that ϵ Eri b’s atmosphere is strikingly similar to that of Jupiter in our solar system. Alternatively, if we do not enforce the dynamical mass (0.98 ± 0.09 M Jup ), a solar metallicity, cloud-free, ≲0.81 M Jup planet would be consistent with the NIRCam upper limit based on the Sonora Flame Skimmer evolutionary models. Finally, we place limits on the size of a potential ring system using the NIRCam/F210M data and discuss the opportunity to directly image ϵ Eri b with additional JWST observations, the Roman Coronagraph Instrument, the ExtraSolar Coronagraph on the Lazuli Observatory, and EELT/METIS.