Blue lightning spotted in Saturn storm

Posted by Emma Woollacott

NASA's Cassini spacecraft has spotted lightning on Saturn in broad daylight, as part of a massive storm last year.

Bluish spots appear in the middle of swirling clouds, indicating flashes of lightning - the first time scientists have ever seen it at visible wavelengths on Saturn's sunlit side.

"We didn't think we'd see lightning on Saturn's day side - only its night side," says Ulyana Dyudina, a Cassini imaging team associate based at the California Institute of Technology in Pasadena. "The fact that Cassini was able to detect the lightning means that it was very intense."

The lightning flashes appear brightest in the blue filter of Cassini's imaging camera; and scientists are still analyzing why. It might be that the lightning really is blue; or perhaps the short exposure of the camera in the blue filter makes the short-lived lightning easier to see.

What is clear is that the lightning is as powerful as anything seen on Earth. The visible energy alone is estimated to be about three billion watts, in a flash lasting for one second.

The flash is around 100 miles across when it exits the tops of the clouds, implying that the lightning bolts originate in the clouds deeper down in Saturn's atmosphere where water droplets freeze - similar to where lightning is created in Earth's atmosphere.

"As summer storm season descends upon Earth's northern latitudes, Cassini provides us a great opportunity to see how weather plays out at different places in our solar system," says Cassini project scientist Linda Spilker.

"Saturn's atmosphere has been changing over the eight years Cassini has been at Saturn, and we can't wait to see what happens next."