Friday, July 20, 2012

Lightning in the Daytime...On Saturn

The above false-color mosaics from NASA's Cassini spacecraft capture lightning striking within the huge storm that encircled Saturn's northern hemisphere for much of 2011. Image Credit: NASA/JPL-Caltech/Space Science Institute

On July 18th, NASA released an image mosaic showing that the Cassini spacecraft had, for the first time, captured lightning on the daytime side of Saturn. The images were taken during the 2011 storm, the largest storm seen up-close by Cassini. Scientists found bluish spots in the middle of the swirling clouds. It turned out that those bluish spots were flashes of lightning.

Scientists expected to see lightning on Saturn's day side, but not the night. The fact that Cassini was able to detect the lightning indicates that it was very intense. The images may be seen at , and .

The images were taken March 6, 2011 and the lightning flashes appeared brightest in the blue filter of Cassini’s imaging camera. Scientists aggressively heightened the blue tint of the image to determine its size and location. Scientists are still 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.

But enough about what the scientists don't know. Let's talk about what the do know...

The intensity of the flash is comparable to the strongest flashes on Earth. The visible energy alone 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.

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.

Cassini is providing a great opportunity to see how weather plays out at different places in our solar system. The mission team has seen the atmosphere of Saturn change over the eight years Cassini has been there, and they can't wait to see what will happen next.

And now, the mission particulars...

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute in Boulder, Colorado.


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