Over that period, the research team watched as the south polar region darkened going into winter and the north polar region brightened as summer approached. By observing the planet at four different points in time, years apart, they could see how the gradual shifting of the seasons affected the planet. The top row shows how the planet appeared when viewing it with just visible light.
The second row from the top is a pseudo-color image based on visible-light and near-infrared observations. Green indicates less methane in the atmosphere than blue, and red indicates the absence of methane. The lower levels of atmospheric methane at the poles (which, remember, are on the planet’s sides rather than its top and bottom) indicate that there is little seasonal variation in methane levels. In the left-most image on this row, the green-colored south pole is moving into darkness. In the other three images, the green, lower-methane region of the north pole can be seen coming into view. (The fourth row shows the same lack of methane variation, but without coloration.)
But what about the third row? This shows estimates of aerosol abundance, using visible light and infrared images that haven’t been colored. The light areas are cloudy with high aerosol abundance, and the dark areas are clear with low aerosol abundance. What is noteworthy in these images is that there is seasonal variation. The arctic region was clear at the beginning of spring (in 2002), but became cloudy as summer progressed (2012 through 2022). Conversely, the antarctic region appears to have cleared as fall progressed into winter. The team believes that these seasonal changes are evidence that sunlight changes levels of aerosol mist on the planet.
Although the results of this study cover a long 20-year period, this still only reflects one period of seasonal change in Uranus’ atmosphere. The research team will continue to observe Uranus as the polar regions move into news seasons, to gather more data.
This story originally appeared on WIRED Japan and has been translated from Japanese.