The cold substellar frontier in JWST Extragalactic surveys: a robust parallax measurement yields the most distant known ultra-cold Y dwarf
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arXiv: 2611.08346v1 · Summary page
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A cold nearby world in a deep view of the Universe
Images collected to study distant galaxies can also uncover exceptionally faint objects in our own neighbourhood. Using repeated JWST observations of the JADES field, researchers measured the parallax of the ultra-cold Y dwarf JADES-GS-BD-5, placing it at 64 parsecs. That makes it the most distant known Y dwarf with a parallax-measured distance. Its motion across the sky is consistent with membership in the Milky Way’s thin disk.
The distance converts apparent faintness into intrinsic luminosity, allowing evolutionary models to place the object in the planetary-mass regime. That is a model-based inference, not a direct weighing. Its faint emission makes it a valuable test of cold giant-planet atmospheres, but current atmospheric models cannot reproduce its full spectral energy distribution in detail. The mismatch points toward the importance of vertical mixing and chemistry that has not settled into equilibrium.
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