WD 0806b

Cold giant exoplanet (or planetary-mass companion) orbiting the white-dwarf WD 0806-661 at an unusually wide 2,500 AU (~50× the Sun-to-Kuiper-belt distance). One of only ~90 directly imaged exoplanets known, and the second-coldest directly imaged exoplanet to date.

Discovery

• Originally identified with the spitzer-space-telescope IRAC instrument in 2011.

2026 JWST atmosphere result

Reported by ben-lew et al. (The Astronomical Journal 2026), summarized in src-aas-nova-wd-0806b-atmosphere-2026-04:

• Combined JWST NIRCam + NIRSpec imaging and spectroscopy with prior data and evolutionary models to constrain mass, radius, surface gravity, and effective temperature.
• NIRSpec retrieval recovered CO₂, CO, and NH₃ abundances.
• The paper develops a novel framework for altitude-dependent K_zz retrieval and reports the first observational evidence that bulk mixing weakens with altitude in an exoplanet atmosphere.

Why it matters

• Tests how giant planets survive and evolve through their host star’s post-main-sequence phase.
• Provides a methodological bridge between brown-dwarf and exoplanet atmosphere retrievals.
• Comparison target for other cold-giant benchmarks such as epsilon-indi-ab.