An Updated Model for Epsilon Eridani b and Prospects for Imaging with the Roman Coronagraph
Abstract
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.
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BibTeX
@misc{llopsayson2026updated,
title = {{An Updated Model for Epsilon Eridani b and Prospects for Imaging with the Roman Coronagraph}},
author = {Jorge Llop-Sayson and Andre Fogal and James Mang and William Thompson and Clarissa R. Do Ó and Aniket Sanghi and Isabela G. Huckabee and Laurent Pueyo and Charles Beichman and Geoffrey Bryden and Marie Ygouf and András Gáspár and Schuyler Wolff and Jarron Leisenring and Dimitri Mawet and Tiffany Meshkat and Caroline V. Morley and Jean-Baptiste Ruffio},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.19131},
eprint = {2609.19131},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19131},
}
RIS
TY - UNPB
TI - An Updated Model for Epsilon Eridani b and Prospects for Imaging with the Roman Coronagraph
AU - Jorge Llop-Sayson
AU - Andre Fogal
AU - James Mang
AU - William Thompson
AU - Clarissa R. Do Ó
AU - Aniket Sanghi
AU - Isabela G. Huckabee
AU - Laurent Pueyo
AU - Charles Beichman
AU - Geoffrey Bryden
AU - Marie Ygouf
AU - András Gáspár
AU - Schuyler Wolff
AU - Jarron Leisenring
AU - Dimitri Mawet
AU - Tiffany Meshkat
AU - Caroline V. Morley
AU - Jean-Baptiste Ruffio
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2609.19131
UR - https://arxiv.org/abs/2609.19131
AB - 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.
ER -