![Post-processed NIRCam images for the two epochs, with 1- and 2-σ contours of the expected position, computed with the posteriors of the Octofitter results: in white without including the images in the fit, and in green including the images, but without making a connection between flux and atmospheric model. The postprocessing method is described in Sec. 2.3. When including the images, some walkers tend towards the feature whose location coincides with the expected position of planet b. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/An-Updated.png?fit=1200%2C682&ssl=1)
[astro-ph.EP] Epsilon Eridani b, the nearest known Jupiter analog, has its orbit and mass constrained from radial velocity (RV) and absolute astrometry, and its atmosphere from JWST/NIRCam imaging upper limits in Sanghi et al. 2026.
Here we follow up that work with a self-consistent model of Epsilon Eridani b that treats all available data within a single Bayesian framework. We extend the RV data with new measurements, update the treatment of the astrometry data with a new model, and include the NIRCam observations with a grid of evolutionary and atmospheric models.
We find a mass of 0.91+-0.06 M_Jup and an orbit consistent with previous work. The imaging data helps constrain planet effective temperature, atmospheric metallicity and surface gravity. The constraints are dependent on model assumptions: for an atmosphere in chemical equilibrium, an otherwise low statistically significant feature in one of the epochs is recovered as the planet at high confidence.
When assuming chemical disequilibrium, the posteriors exhibit a bimodal distribution, with one mode consistent with zero flux and the other coinciding with the flux of the tentative feature. Consistent with previous work, the clear atmosphere models are found to be viable at very enhanced metallicity, whereas the cloudy models yield more moderate values.
Applying these models to the Roman Coronagraph, we find that the predicted reflected-light fluxes place every cloudy atmosphere our fit allows within the instrument’s expected sensitivity. A non-detection would be very constraining: a final contrast sensitivity of 2e-9 would rule out all cloudy atmospheres under our model assumptions.
Visualization of the MIRI disk (S. G. Wolff et al. 2025) and planet orbit relative positions. The mutual inclination resulting from our fits is Φ=14±4◦ , the inclination of the disk is ∼34◦ , and the planet’s, 43±4◦ . The inner edge of the displayed disk image is 2.7 au, where the MIRI PSF core saturates at 25.5 µm. — [astro-ph.EP]
Jorge Llop-Sayson, Andre Fogal, James Mang, William Thompson, Clarissa R. Do ‘O, Aniket Sanghi, Isabela G. Huckabee, Laurent Pueyo, Charles Beichman, Geoffrey Bryden, Marie Ygouf, Andr’as G’asp’ar, Schuyler Wolff, Jarron Leisenring, Dimitri Mawet, Tiffany Meshkat, Caroline V. Morley, Jean-Baptiste Ruffio
Comments: Submitted to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.19131 [astro-ph.EP] (or arXiv:2609.19131v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.19131
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Submission history
From: Jorge Llop-Sayson
[v1] Wed, 16 Sep 2026 17:51:25 UTC (6,723 KB)
https://arxiv.org/abs/2609.19131
Astrobiology,
