Overview
- A Northwestern‑led team used JWST’s NIRSpec to record the first direct spectrum of GJ 504 b, a faint companion about 57 light‑years away, and published the peer‑reviewed results on June 18, 2026.
- The spectrum shows multiple molecules — water, methane, carbon monoxide, carbon dioxide, ammonia and hydrogen sulfide — plus signs of disequilibrium chemistry that indicate vertical mixing in the atmosphere.
- Atmospheric retrievals that omitted clouds produced physically implausible results, while models that include a deck of condensed salt clouds gave the best fits to the 2.9–5.3 micron data.
- The salt layer is an inference from model fits rather than a directly imaged feature, and the team stresses that cloud identification depends on retrieval assumptions and remains to be confirmed.
- GJ 504 b sits near the ~25 Jupiter‑mass boundary between planets and brown dwarfs, so the spectrum’s hint of heavy‑element enrichment suggests but does not prove planet‑like formation and drives planned JWST follow‑ups and modeling refinements.