Overview
- A Northwestern‑led team used the James Webb Space Telescope to obtain a high‑quality direct spectrum of GJ504b and found that models must include salt clouds to match the data.
- The spectrum shows clear molecular signatures including water vapor, methane, carbon dioxide, ammonia and hydrogen sulfide, but those deeper features are muted by a cloud layer.
- Including chloride or sulfide salt clouds resolved an earlier isothermal/opacity anomaly and produced physically plausible retrievals of temperature, radius and mass.
- The revised estimates place GJ504b at roughly 25 Jupiter masses, about 10% smaller than Jupiter in radius, and near 290°C, a range that leaves its formation as a planet or brown dwarf unresolved.
- Researchers say the result both demonstrates Webb's ability to study very cold, faint companions and calls for targeted follow‑up JWST spectroscopy to confirm cloud composition and pin down formation history.