A Jupiter-sized brown dwarf located 7.5 light-years away has revealed variable water clouds in its atmosphere, marking a significant discovery in exoplanetary science. Brittany Miles, an assistant astronomer at the University of Arizona Steward Observatory, led a research team that utilized the James Webb Space Telescope (JWST) for an 11-hour observation period of WISE 0855, the coldest known brown dwarf.

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The study, published in The Astrophysical Journal, provides a detailed time-series analysis of WISE 0855, confirming that its water clouds change thickness over time, similar to weather patterns on Earth. The findings indicate that the brown dwarf's atmosphere is influenced by at least two processes: high-altitude water clouds that fluctuate in density as the body rotates, and deeper chemical gases being brought upward by convective currents.

Miles stated, "This is the first time we've been able to confirm that water clouds are becoming thinner and thicker on a nearby world," emphasizing that prior telescopes could not distinguish between the effects of clouds, chemistry, and temperature.

Brown dwarfs, which are larger than planets but not massive enough to ignite fusion like stars, emit faint heat from their creation. With a temperature of about 265 Kelvin, colder than Earth's surface, WISE 0855 presents a unique case as it closely resembles a large, free-floating planet.

Co-author Mark Marley noted, "The photons go through the atmosphere and escape to space," likening the observation of WISE 0855 to viewing through a "screen door." As the brown dwarf rotates, different areas with varying cloud cover and temperatures are observed, providing insights into its dynamic atmosphere.

The JWST's medium-resolution spectrograph captured fluctuations in temperature and a wave-like signal related to specific gases such as carbon monoxide and phosphine, indicating active convection processes similar to those on Jupiter.

"We're seeing water clouds getting thicker and thinner, and deep gases rising and falling, and we can actually watch them change in real time," said Miles.

This discovery has broader implications for understanding the atmospheres of other celestial bodies. If the physics of convection, clouds, and chemical processes seen in Jupiter apply to WISE 0855, it could extend to gas giant exoplanets currently under investigation with JWST.

Miles highlighted the significance of the findings, noting that brown dwarfs exhibit planet-like behaviors despite not being true planets, thus blurring the distinctions between these types of celestial objects. Looking forward, she aims to conduct more observations with JWST to refine their understanding of WISE 0855's atmospheric dynamics.