# JWST measures parallax of Y dwarf JADES-GS-BD-5: 64 pc, about 3× farther than known Y dwarfs

- Published: 2026-11-06 05:04 UTC
- Section: Sky & Space › Astronomy
- Tags: JADES-GS-BD-5, Y dwarf parallax, cold brown dwarf, JWST NIRCam, JADES GOODS-South, planetary-mass object, bolometric luminosity, proper motion
- URL: https://realtech.media/news/rt-1079c62038aeb40463f760e8_jwst_measures_parallax/

**Multi-epoch NIRCam imaging over about 2 years gave a parallax of 15.7 mas for a cold brown dwarf in the JADES field, the first such measurement in a JWST extragalactic deep field.**

![JWST measures parallax of Y dwarf JADES-GS-BD-5: 64 pc, about 3× farther than known Y dwarfs](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/2a75c993ba13d618.jpg)
*NASA/MSFC/David Higginbotham/Emmett Given, Wikimedia Commons, Public domain*

The authors of an arXiv · preprint (not yet peer reviewed) analyse JADES-GS-BD-5, an extremely cold Y dwarf identified in the JADES/GOODS-South field. Using multi-epoch JWST/NIRCam imaging over a baseline of about 2 years, they calibrated the telescope's astrometry and obtained what they describe as the first robust parallax for a brown dwarf discovered in a JWST extragalactic deep field [1].

## Distance and motion

The measured proper motion is 49.8 ± 0.3 mas per year, and the parallax is 15.7 (+1.4/−1.3) mas. This corresponds to a geometric distance of 64 (+6/−5) pc, about 3 times farther than the previously known most distant Y dwarfs with parallax-measured distances [1]. The tangential velocity is 15.0 (+1.4/−1.3) km/s, consistent with a Galactic thin-disk object. The authors found no evidence for binary acceleration, significant photometric variability or a plausible host.

For context, Y dwarfs radiate mostly at 4–5 µm, which makes ground-based astrometry difficult. All known Y dwarfs lie within 20 pc of the Sun, and their parallaxes have so far required dedicated Spitzer and HST campaigns. The coldest end of the sequence relies almost entirely on WISE 0855 at 2.28 pc.

## Classification and atmosphere

The J-band spectral morphology of JADES-GS-BD-5 is consistent with existing Y-dwarf templates. Its very low luminosity and its near-infrared spectral profile confirm that it is one of the coldest dwarfs discovered to date. The authors adopt a classification of >Y1, in line with a NIRCam colour-based proxy of cY1.5 [1].

With the parallax distance, the bolometric luminosity is log(L/L☉) = −7.08 ± 0.09. Evolutionary modelling places the object in the planetary-mass regime, which makes it a benchmark for the study of cold giant-planet atmospheres.

Current atmospheric models do not reproduce its spectral energy distribution in detail. According to the authors, this points to the importance of disequilibrium chemistry and vertical mixing. Water deficiency may also contribute, but the evidence for it is currently unclear.

The paper also reports additional proper-motion measurements for eight of the other nine known JADES Y-dwarf candidates.

## Sources

1. [arXiv · препринт](https://arxiv.org/abs/2611.08346v1)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-1079c62038aeb40463f760e8_jwst_measures_parallax/