Imagine an electrical storm larger than the continental United States in which the lightning bolts are more than 1,000 times stronger than conventional lightning, and you'll have a good idea of what can transpire on Saturn. NASA's Cassini spacecraft has recently captured images of lightning on Saturn. The images have allowed scientists to create the first movie showing lightning flashing on another planet. After waiting years for Saturn to dim enough for the spacecraft's cameras to detect bursts of light, scientists were able to create the movie, complete with a soundtrack that features the crackle of radio waves emitted when lightning bolts struck.
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is famous for its rings but also has raging lightning storms.
The NASA supplied movie and radio data suggest extremely powerful storms with lightning that flashes as bright as the brightest super bolts on Earth, according to Andrew Ingersoll, a Cassini imaging science subsystem team member at the California Institute of Technology in Pasadena. "What's interesting is that the storms are as powerful -- or even more powerful - at Saturn as on Earth," said Ingersoll. "But they occur much less frequently, with usually only one happening on the planet at any given time, though it can last for months."
Since early 2005, scientists have been tracking lightning on Saturn, primarily found by Cassini. Saturn has powerful lightning storms, 10,000 times stronger than on Earth, that occur in huge, deep thunderstorms columns nearly as large as the entire Earth. The storms occasionally burst through to the planet's visible cloud tops.
The 2009 thunderstorm that began in January on Saturn is the ninth that has been measured since Cassini swung into orbit around Saturn in July 2004. Lightning discharges in Saturn's atmosphere emit very powerful radio waves, which are measured by the antennas and receivers of Cassini. These radio waves are about 10,000 times stronger than their terrestrial counterparts and originate from huge Saturnian thunderstorms.
To make a video, scientists needed more pictures with brighter lightning and strong radio signals. The necessary data was collected during a shorter storm, which occurred from November through mid-December 2009. The frames in the video were obtained over 16 minutes on Nov. 30, 2009. The flashes lasted less than one second. The images show a cloud as long as 1,900 miles across and regions illuminated by lightning flashes about 190 miles in diameter.
When lightning strikes on Earth and on Saturn, it emits radio waves at a frequency that can cause static on an AM radio. The sounds in the video approximate that static sound, based on Saturn electrostatic discharge signals detected by Cassini's radio and plasma wave science instrument.
Since Cassini's arrival at Saturn in 2004, it has been difficult to see the lightning because the planet is very bright and reflective. Sunlight shining off Saturn's enormous rings made even the night side of Saturn brighter than a full moon night on Earth. Equinox, the period around August 2009 when the sun shone directly over the planet's equator, finally brought the needed planetary darkness. During equinox, the sun lit the rings edge on only and left the bulk of the rings in shadow.
For further information and the video: http://www.jpl.nasa.gov/news/news.cfm?release=2010-129&rn=news.xml&rst=2564