July 19, 2012
Saturn Lightning Caught By Cassini
Lawrence LeBlond for redOrbit.com - Your Universe Online
NASA´s Cassini satellite, which has been visiting Saturn now for eight years, caught a rare daytime lightning strike in a massive storm that has been plaguing the northern hemisphere of the distant ringed-planet for most of 2011.
The spacecraft caught the images on March 6, 2011 and marks the first time scientists have been able to detect lightning in visible wavelengths on Saturn´s illuminated surface (side facing the Sun). The images were surprising to the scientists, because previously they were only able to see lightning on the dark side of the planet.
“The fact that Cassini was able to detect the lightning means that it was very intense,” said Ulyana Dyudina, an imaging associate on the Cassini team at the California Institute of Technology (Caltech) in Pasadena, California.
The lightning flashes appear brightest in the blue filter of Cassini´s imaging camera. To garner a better picture of the lightning strike, the team heightened the blue tint, but remain puzzled as to why the blue filter even catches the lightning. It´s possible that the lightning really is blue, or it might be that the short exposure of the camera in the blue filter makes the lightning strike easier to see. In any case, the team is continuing to analyze the data.
The intensity of the flash is comparable to the strongest flashes ever observed on Earth. The visible energy alone has been estimated to be about 3 billion watts. The flash is about 100 miles in diameter when it exit´s the top of the clouds. From the data gleaned, the team made a reasonable judgment that the lightning strikes originate deep down in the clouds at the point where water droplets would freeze. This is comparable to where lightning is created in our own atmosphere here on Earth, the team said.
Cassini captured multiple images, creating a complex view of the storm that wrapped around Saturn´s northern hemisphere throughout the bulk of 2011. In one composite image, Cassini captured five lightning flashes, and in another, three flashes.
“Cassini provides us a great opportunity to see how weather plays out at different places in our solar system,” said Linda Spilker, a Cassini project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena. “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 the featured image, the left panel shows the lightning flash, appearing as a blue dot. The mosaic on the right is composed of images taken 30 minutes later by Cassini, showing there is no lightning flashing at that time. The lightning only appeared in the filter sensitive to blue visible light, and the images were enhanced to increase the visibility of the lightning.
The images were captured with a narrow-angle camera aboard Cassini. They were taken on March 6, 2011 from a distance of about 2 million miles from Saturn.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI). The mission is managed by the JPL, a division of Caltech, for NASA´s Science Mission Directorate. Cassini and its cameras were designed and developed at JPL. The imaging team is based at the Space Science Institute in Boulder, Colorado.