2026/03/09 by Aniket Sanghi, William Thompson, James Mang +21 · 2 voices · 3 citations
#astro-ph.EP #astro-ph.SR
We present new JWST/NIRCam 4-5 μm (F410M, F430M) and JWST/MIRI 18-25 μm (F1800W, F2100W, F2550W) imaging detections of the nearby (3.6 pc) cold (275 K) gas giant exoplanet ε Ind Ab. The F2550W detection of ε Ind Ab constitutes the longest wavelength image of an exoplanet acquired to date. Combining three decades of radial velocity monitoring, Gaia-Hipparcos absolute astrometry, and relative astrometry from direct imaging (including the new NIRCam astrometry), we conduct a comprehensive re-analysis of ε Ind Ab's orbit and obtain a dynamical mass M\rm Ab = 6.5+0.7-0.6 M\rm Jup. Using ε Ind Ab's NIRCam and MIRI photometry, we assemble the first 4-25 μm spectral energy distribution (SED) of a cold gas giant outside the Solar System. The NIRCam photometry supports a metal-enriched atmosphere for ε Ind Ab based on analysis with atmospheric model grids, consistent with predictions from the giant planet mass-metallicity relation. While the current data do not provide definitive evidence for or against the presence of water ice clouds, we tentatively find that the H2O vapor absorption-dominated F2550W photometry is systematically brighter (>1σ, but <2σ) than predictions from cloud-free/rainout chemistry models and better explained by a cloudy model. We calculate a bolometric luminosity of log L\rm bol/L_\odot = -7.23 ± 0.03 dex by directly integrating ε Ind Ab's SED. Combining this with the planet's dynamical mass and age (3.5 ± 1.0 Gyr), we demonstrate excellent agreement with evolutionary model predictions in a new regime of low luminosities, low masses, and old ages. Our results establish ε Ind Ab as a benchmark system for planetary evolution studies and set the stage for the detailed atmospheric characterization of this temperate extrasolar world.