Worlds Next Door. IV. Mapping the Late Stages of Giant Planet Evolution with a Precise Dynamical Mass and Luminosity for $ε$ Ind Ab
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| Natura: | Preprint |
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2026
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| author | Sanghi, Aniket Thompson, William Mang, James Xuan, Jerry Mawet, Dimitri Ruffio, Jean-Baptiste Zhang, Yapeng Wang, Jason Morley, Caroline Nielsen, Eric Roberson, William Matthews, Elisabeth Carter, Aarynn Crossfield, Ian Mâlin, Mathilde Benneke, Björn Bidot, Alexis Gáspár, András He, Carrie Horstman, Katelyn Madurowicz, Alexander Marois, Christian Oppenheimer, Rebecca Perrin, Marshall |
| author_facet | Sanghi, Aniket Thompson, William Mang, James Xuan, Jerry Mawet, Dimitri Ruffio, Jean-Baptiste Zhang, Yapeng Wang, Jason Morley, Caroline Nielsen, Eric Roberson, William Matthews, Elisabeth Carter, Aarynn Crossfield, Ian Mâlin, Mathilde Benneke, Björn Bidot, Alexis Gáspár, András He, Carrie Horstman, Katelyn Madurowicz, Alexander Marois, Christian Oppenheimer, Rebecca Perrin, Marshall |
| contents | We present new JWST/NIRCam 4-5 $μ$m (F410M, F430M) and JWST/MIRI 18-25 $μ$m (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 $μ$m 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 H$_2$O 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 $\log L_{\rm bol}/L_\odot = -7.23 \pm 0.03$ dex by directly integrating $ε$ Ind Ab's SED. Combining this with the planet's dynamical mass and age ($3.5 \pm 1.0$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_08787 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Worlds Next Door. IV. Mapping the Late Stages of Giant Planet Evolution with a Precise Dynamical Mass and Luminosity for $ε$ Ind Ab Sanghi, Aniket Thompson, William Mang, James Xuan, Jerry Mawet, Dimitri Ruffio, Jean-Baptiste Zhang, Yapeng Wang, Jason Morley, Caroline Nielsen, Eric Roberson, William Matthews, Elisabeth Carter, Aarynn Crossfield, Ian Mâlin, Mathilde Benneke, Björn Bidot, Alexis Gáspár, András He, Carrie Horstman, Katelyn Madurowicz, Alexander Marois, Christian Oppenheimer, Rebecca Perrin, Marshall Earth and Planetary Astrophysics Solar and Stellar Astrophysics We present new JWST/NIRCam 4-5 $μ$m (F410M, F430M) and JWST/MIRI 18-25 $μ$m (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 $μ$m 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 H$_2$O 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 $\log L_{\rm bol}/L_\odot = -7.23 \pm 0.03$ dex by directly integrating $ε$ Ind Ab's SED. Combining this with the planet's dynamical mass and age ($3.5 \pm 1.0$ 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. |
| title | Worlds Next Door. IV. Mapping the Late Stages of Giant Planet Evolution with a Precise Dynamical Mass and Luminosity for $ε$ Ind Ab |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2603.08787 |