Worlds Next Door. III. Indirect Evidence for Enhanced Atmospheric Metallicity and/or the Presence of Water Clouds in the Nearest Jupiter-analog $ε$ 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 4-5 $μ$m (F444W). We achieve a 5$σ$ contrast sensitivity $\approx3.0\times10^{-7}$ ($Δ\approx 16.3$ mag) in the F444W filter at the expected planet separation of $\approx$1". This is the deepest 4-5 $μ$m contrast performance achieved for any JWST/NIRCam observation to date at these separations (and $>10\times$ better than ground-based limits). Yet, the planet remains elusive to imaging. We update the star's age to $1.1\pm0.1$ Gyr, older than previous age estimates, using the latest gyrochronology relations. This significantly impacts $ε$ Eri b's inferred effective temperature ($T_{\rm eff}$), which is now expected to lie between 150-200 K based on evolutionary models for a 1 $M_{\rm Jup}$ planet. Using cloud-free Sonora Flame Skimmer models and custom PICASO patchy cloud models in the above $T_{\rm eff}$ range, we find that the F444W non-detection 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 ($0.98 \pm 0.09\;M_{\rm Jup}$), a solar metallicity, cloud-free, $\lesssim0.81\;M_{\rm Jup}$ 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.

Figures (14)

• Figure 1: Effective temperature ($T_{\rm eff}$) versus rotation period for $\epsilon$ Eri compared to data from three young age-dated clusters compiled by bouma_empirical_2023. Original sources of cluster data: NGC 6811 curtis_temporary_2019, Praesepe rampalli_three_2021, NGC 3532 fritzewski_rotation_2021, Group-X messina_gyrochronological_2022.
• Figure 2: Top: Raw coronagraphic image of $\epsilon$ Eri from the observations presented in llop-sayson_searching_2025. The solid and dotted white contours mark the 1$\sigma$ and 2$\sigma$ posterior predictions for $\epsilon$ Eri b's position, respectively. The expected position overlaps with one of the bright PSF lobes, which created strong residuals after PSF subtraction llop-sayson_searching_2025. Bottom: Same as the top panel for the observations presented in this work. The expected position of $\epsilon$ Eri b does not overlap with the bright PSF lobes.
• Figure 3: Upper limits on the F444W and F210M flux ratio of $\epsilon$ Eri b with respect to the host star from deep JWST/NIRCam imaging observations. Left column: S/N measured in an image following mawet_fundamental_2014 that corresponds to a 5$\sigma$ significance detection as a function of separation for observations in F444W (top) and F210M (bottom). Center column: Retrieved S/N for a synthetic companion injected at various contrast ratios at 1 separation, averaged across multiple position angles, for the reduction geometry noted in the title (using 10 principal components). The S/N equivalent to 5$\sigma$ significance is marked with a horizontal dashed line. Right column: The ADI+RDI PSF subtracted images of $\epsilon$ Eri in both filters for the reduction geometries in the center panel with an example synthetic companion injected at the contrast ratio corresponding to 5$\sigma$ detection significance. The expected location of $\epsilon$ Eri b on 2025 August 29 thompson_revised_2025 is shown with a '$+$' marker and the corresponding 1$\sigma$ (solid) and 2$\sigma$ (dotted) uncertainty contours. No significant point source signal is recovered at $\epsilon$ Eri b's expected location.
• Figure 4: 5$\sigma$ calibrated contrast curve for F210M (blue) and F444W (red) observations of $\epsilon$ Eri. The dark and light gray shaded regions correspond to the 1$\sigma$ and 2$\sigma$ separation range expected for the planet.
• Figure 5: Distribution of signal-to-noise ratios (SNRs) of pixels from the F444W PSF-subtracted image in a 2 FWHM width annulus centered at a separation of 1 compared to a standard normal distribution.