So what could be causing these brightness variations? After all, a brown dwarf doesn't have surface features like bright ice caps and dark lava flows that one would expect on the solid surface of a rocky planet.
Brown dwarfs are sub-stellar objects that are too small to ignite long-term fusion in their cores (therefore they're not stars) and they don't exhibit chemical differentiation by height (therefore they're not planets). Brown dwarfs are rather mysterious in that they exist in a stellar hinterland, bridging the gap between the largest planets and the smallest stars.
If the observed brightness changes aren't caused by surface features (as there's no "surface"), what could it be?
"The best explanation is that brighter and darker patches of its atmosphere are coming into our view as the brown dwarf spins on its axis," said Radigan.
Co-author Ray Jayawardhana, Canada Research Chair in Observational Astrophysics at the University of Toronto, agrees: "We might be looking at a gigantic storm raging on this brown dwarf, perhaps a grander version of the Great Red Spot on Jupiter in our own solar system, or we may be seeing the hotter, deeper layers of its atmosphere through big holes in the cloud deck."