Observe well the video that accompanies these lines and hear their crackling sound. The images may be somewhat blurred, in these times of high definition, but what you see and hear them too well justified: it is in fact the first recorded thunderstorm outside the Earth. The scene is the dark side of Saturn and the instruments used are the cameras of the Cassini probe. The work has been published in Geophysical Research Letters.
Since Cassini arrived at Saturn in 2004, scientists have been collecting radio signals that clearly indicated that thunderstorms occur relatively frequently in the ringed planet, but so far not been able to see one of those tormetas with their own eyes.
The main reason for this is that Saturn is an extremely bright world. Its enormous ring system acts, in fact, like a mirror, reflecting on the surface by sunlight and that even in its night side, the planet shines with an intensity similar to that of the full moon on Earth. Too much light for photographs.
After that period, during which the sun’s rays light up the rings and perpendicular fall to lead Ecuador, came at last, the moment when the shadows invaded a part of the planet, allowing scientists to make their comments. The result has been that for the first time since his arrival, Cassini has been able to photograph a lightning storm, a milestone that has enabled researchers to produce a video without precedent in the scientific literature.
“It’s the first time we have the glow of the rays with radio data,” said Georg Fischer, the Space Research Institute Graz, Austria. ”Now that we have been able to align the radio data with the visible light we are completely sure that what we are seeing are powerful thunderstorms.”
The original video lasts 16 minutes and has been compressed by astronomers in the ten seconds that are along these lines. The cloud in which rays are produced is just over 3,000 km.in its longest side, and each flash has dimensions of about 300 km and an energy release comparable to the strongest rays here on Earth. Each hard real-time about one second.
“It’s very interesting,” said Andrew Ingersoll, an investigator of the Cassini-storms that are as strong or even stronger, on Saturn than on Earth. Only here occur much less frequently, usually only one in the entire planet for a given time, but with a duration of several months. ”
The crackling sound that accompanies the images is synthetic and is close to receiving the actual sound recording instruments on Cassini, which is well above the hearing range of humans. When rays are produced (either in Saturn or on Earth) they emit radio waves at a frequency that is capable of causing the kind of static noise can often be heard on a radio station. The video sounds like the same static, and are based on electrostatic discharge signals detected by instruments on Cassini at Saturn.
The first ray images were collected in August 2009, during an electrical storm that lasted from January to October this year and is, in fact, the largest and longest few have been observed so far in the Solar System.