Researchers at Trinity College Dublin used observations from NASA's James Webb Space Telescope to investigate SIMP 0136, a brown dwarf previously associated with phenomena resembling the northern lights. They applied a mathematical technique called Principal Component Analysis (PCA) to examine how the object's light varied as it rotated.
The analysis revealed that nearly all of the observed atmospheric variability could be explained by just two dominant components: temperature fluctuations and changes in the vertical arrangement of clouds. Rather than beginning with detailed assumptions about how the atmosphere should behave, the researchers allowed the observations to reveal the most important processes. The method also helped separate genuine atmospheric changes from minor fluctuations and random noise in the measurements.
Webb's exceptionally sensitive instruments made this possible by detecting extremely small changes in brightness as different parts of the atmosphere rotated into view.
The researchers also identified three recurring weather states that appear and disappear as the brown dwarf rotates. Together, these states create a shifting atmospheric patchwork. Some regions are hotter and have thinner clouds, while others are cooler and contain thicker cloud layers that extend farther vertically through the atmosphere.
Instead of constantly changing in an unpredictable way, these weather patterns appear to follow an underlying structure.
SIMP 0136 is larger and hotter than a typical gas giant planet, but it lacks the mass needed to shine like a star. Its atmosphere contains enormous cloud systems that evolve rapidly, making its weather more comparable to an extreme version of what might be found on a gas giant exoplanet.
The discovery offers a new way to understand the atmospheric conditions of distant worlds and could help astronomers investigate planets far beyond our Solar System. The findings were published in Astronomy & Astrophysics.