JWST finds water clouds on the coldest known brown dwarf WISE 0855

The James Webb Space Telescope observed WISE 0855, the coldest known brown dwarf just 7.2 light-years away, for 11 hours. NIRSpec data confirmed patchy water-ice clouds at 1–4 bar and updrafts of carbon monoxide, carbon dioxide and phosphine from deeper layers.

• WISE 0855 lies 7.2 light-years away with an upper atmosphere near 265 K
• NIRSpec captured 44 spectra every 15 minutes from 2.87 to 5.27 microns
• Brightness in the CO band swung by 10% over one rotation
• PICASO and coolTLUSTY models fit far better with water clouds included