Overview
- A Northwestern-led team used the James Webb Space Telescope to obtain a direct spectrum of GJ504b that reveals water vapor, methane, carbon dioxide and ammonia and required only two hours of observing time.
- Models without clouds produced a physically implausible isothermal layer, but adding salt clouds made the spectrum self-consistent, giving the first direct spectroscopic evidence that chloride and/or sulfide clouds veil the atmosphere.
- The object remains a cold, pink-hued planetary-mass companion about 25 times the mass of Jupiter with an estimated temperature near 290°C and an age around 2.5–4 billion years.
- The new spectra confirm heavy-element enrichment but do not settle whether GJ504b formed like a giant planet or like a brown dwarf, so its true origin and precise cloud makeup remain unresolved.
- The result demonstrates Webb’s ability to characterize very faint, cold companions and signals broader shifts in atmospheric retrievals because clouds can strongly bias inferred compositions and formation conclusions, prompting planned JWST follow-up.