Patchy water clouds and chemical changes observed on brown dwarf WISE 0855

WISE 0855 is the coldest brown dwarf known, with a temperature of approximately 265 Kelvin. Recent observations using the James Webb Space Telescope reveal that this cool object possesses patchy water clouds and undergoes significant chemical changes in its atmosphere. These findings help clarify the complex weather patterns occurring on substellar objects that bridge the gap between giant planets and stars.

Star system: WISE 0855-0714 | Distance from the Sun: 7.3 light years

WISE 0855 represents the coldest known brown dwarf, an object too large to be a planet but too small to sustain the nuclear fusion that powers stars. With a temperature of roughly 265 Kelvin, it is cold enough to host complex atmospheric phenomena similar to those seen on gas giant planets in our solar system. Observations reveal that this object is not uniform but features patchy water clouds distributed throughout its atmosphere, which influence its light patterns over time.

To study this, researchers used the James Webb Space Telescope to collect time-series data over an 11-hour period. By analyzing infrared light, they were able to separate the effects of temperature, chemical composition, and cloud structure. The data shows that the concentration of gases like carbon monoxide and phosphine fluctuates over time, with these changes appearing to be linked to deep, quenched atmospheric pressures. In contrast, the varying thickness of the water cloud layers appears to occur at higher, lower-pressure regions of the atmosphere.

These patterns provide a detailed look at the dynamic weather cycles on one of the coolest substellar objects in the neighborhood of the Sun. By comparing the observed light fluctuations with atmospheric models, it becomes clear that chemical variations and cloud movement drive the observable changes in the light emitted from WISE 0855.

Key findings
WISE 0855 displays evidence of patchy water clouds within its atmosphere.
Carbon monoxide absorption shows significant time-variable changes with a peak-to-peak amplitude reaching 10 percent.
Variations in carbon monoxide and phosphine concentrations are correlated.
Chemical gas abundances appear to be influenced by deep atmospheric pressure levels.
Cloud thickness variations occur at lower pressures within the atmosphere.

Scientific study

Water Cloud and Chemical Modulations in the Coldest Brown Dwarf (external link)