For the first time in history, scientists have observed visible flashes of extraordinarily powerful lightning on the daytime side of Saturn.
The achievement, announced Wednesday, came from NASA's Cassini spacecraft during a storm on the ringed planet last year.
"We didn't think we'd see lightning on Saturn's day side -- only its night side," said 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 appears brightest in the blue filter of Cassini's imaging camera on March 6, 2011. The imaging team is analyzing why the blue filter catches the lightning. It might be that the lightning really is blue, or it might be that the short exposure of the camera in the blue filter makes the short-lived lightning easier to see.
The visible energy in the lightning is estimated to be about 3 billion watts lasting for one second. The flash is approximately 100 miles (200 kilometers) in diameter when it exits the tops of the clouds. From this, scientists deduce that the lightning bolts originate in the clouds deeper down in Saturn's atmosphere where water droplets freeze. This is analogous 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," said Linda Spilker, Cassini project scientist, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "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."
In composite images that show the band of the storm wrapping all the way around Saturn, scientists have seen multiple flashes. In one composite image, they recorded five flashes, and in another, three flashes.