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Changing seasons provide some of the most spectacular scenery here on Earth. New observations from the Hubble Space Telescope provide evidence that Neptune, too, experiences seasonal weather variation.
Neptune is notorious for its severe weather, including winds that can reach speeds of up to 900 miles an hour, but previous research gave no indication of changing seasons on the planet. A report published in the current issue of journal Icarus indicates otherwise. Researchers from the University of Wisconsin-Madison and NASA's Jet Propulsion Laboratory made three sets of observations of the planet over a six-year period and discovered transformations in the clouds encircling the planet's southern hemisphere. "Neptune's cloud bands have been getting wider and brighter," says Lawrence A. Sromovsky of the University of Wisconsin-Madison. "This change seems to be a response to seasonal variations in sunlight, like the seasonal changes we see on Earth."
Neptune's seasonal shifts do differ from the ones that occur on our planet, however. For one, a single Neptunian season can last more than 40 years. That's because although the axis of Neptune is tilted at an angle similar to that of Earth in relation to the sun, Neptune takes 165 years to orbit the star. Indeed, the scientists say it's remarkable that the weather is responding to changes in the sun's heat at all, considering that the radiation is 900 times weaker on Neptune than it is on Earth. Notes Sromovsky, "It must be a well-lubricated machine that can create a lot of weather with very little friction."