Springtime on Neptune

Forget April in Paris. Instead, try Neptune in spring.

On the distant ice planet, spring is no fleeting season. It lasts for 40 years.

The discovery has surprised astronomers, who didn’t expect seasons to change on a planet where temperatures never rise above 290 degrees below zero and the sun is 900 times dimmer than on Earth.

On Neptune, it’s not cherry blossoms and chirping warblers that herald the coming of spring. It’s a brightening of banded clouds in the planet’s southern hemisphere.

The brightening was noticed by a team of astronomers from the University of Wisconsin at Madison and NASA’s Jet Propulsion Laboratory in Pasadena who have been monitoring the planet for six years.

The finding, published this month in the planetary science journal Icarus, is the first to suggest seasons on the planet. Observations were made using the Hubble Space Telescope. The planet’s cloud belt is expected to continue to brighten for 20 more years -- until the 40-year summer hits.

The changes in Neptunian clouds, like the seasons on Earth, are a response to variations in sunlight.

Neptune is known for its strange, violent weather. The storms and seasonal changes are expected only on planets with more heat.

“Why don’t we see the same thing on Uranus, which is substantially closer to the sun?” asked Kevin Baines, a JPL researcher on the project. “That’s one of the questions we still have to answer.”