NASA’s Cassini spacecraft has captured images of lightning on Saturn, allowing the scientists to create the first movie showing lightning flashing on another planet. “Ever since the beginning of the Cassini mission, a major goal of the Imaging Team has been the detection of Saturnian lightning,” said team leader Carolyn Porco in an email. Porco said the ability to capture the lightning was a direct result of the dimming of the ringshine on the night side of the planet during last year’s Saturn equinox. “And these flashes have been shown to be coincident in time with the emission of powerful electrostatic discharges intercepted by the Cassini Radio and Plasma Wave experiment,” Porco added.
The sound in the video approximates the electrostatic discharge signals detected by the instrument.
“The process of electrostatic discharge and lightning production is tied to the motions of electrically charged particles and molecules in the Earth’s atmosphere,” Porco said, “and the same is believed to be true for the atmospheres of the giant planets. Measuring the power of lightning strikes in a planetary atmosphere can tell of the energy contained in the thunderstorms that spawn them and of the vigor of the atmospheric motions.”
The movie and radio data suggest extremely powerful storms with lightning that flashes as brightly 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.”
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The first images of the lightning were captured in August 2009, during a storm that churned from January to October 2009 and lasted longer than any other observed lightning storm in the solar system. Results are described in an article accepted for publication in the journal Geophysical Research Letters.
The data collected in order to make a video came in November through mid-December 2009 during a shorter storm that included brighter lightning and stronger radio signals. 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 3,000 kilometers (1,900 miles) across and regions illuminated by lightning flashes about 300 kilometers (190 miles) in diameter. Scientists use the width of the flashes to gauge the depth of the lightning below the cloud tops.