Webb watched water clouds thin and thicken on the coldest known brown dwarf
WISE 0855 is the coldest brown dwarf anyone has found, at about 265 K (−8 °C), and it sits 2.28 parsecs (about 7.4 light-years) from the Sun. A team led by Brittany Miles of the University of Arizona’s Steward Observatory pointed JWST’s NIRSpec spectrograph at it for 11 hours, taking a spectrum every 15 minutes. As the object rotated, the spectra changed in two separate ways. High in the atmosphere, the team finds patchy water clouds whose thickness varies from one side to the other. Deeper down, carbon monoxide and phosphine rise and fall together, which the team reads as temperature changes in gas welling up from the interior. The paper, “Water Cloud and Chemical Modulations in the Coldest Brown Dwarf”, is on arXiv and listed as accepted to The Astronomical Journal. The University of Arizona announced it on 9 October. ...