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The Planetary Society Blog
By Emily Lakdawalla
Biggest lightning storm ever spotted at Saturn
Feb. 16, 2006 | 14:12 PST | 22:12 UTC
There were a couple of press releases out this week about a huge storm at Saturn that is generating more lightning activity than has ever been observed before, even when you include Voyager data. The flash rate is about 0.6 per second, while the peak flash rate observed by Voyager was only about 0.2. The discovery was made with the Radio and Plasma Wave Science (RPWS) instrument, which detects radio emissions. You can listen to the sound of the lightning storm here (it's a 218k WAV file), or you can visit the RPWS site to listen to it along with an animated view of the actual RPWS data from which they made the sound.
I enjoy all the sounds that the RPWS team makes from their data. I and one of my bosses Bruce Betts have an ongoing disagreement about how "real" or "fake" such audio representations of radio data are. Here's my side of the argument: All of these so-called sounds are created from electromagnetic radiation that propagates through a vacuum -- something sound cannot do. So these scientist-created sounds do not in fact represent any real sounds being broadcast through space. However, converting the radio data to sound is a way of permitting us humans to use our sound processing brain power to help us observe what is going on in the radio emission data. With our ears, we can detect and analyze patterns in the sounds that may not be immediately obvious within the numerical data or within graphical representations of it. To me, it's no more "fake" than presenting, say, topographic information as a range of colors on a map. And it's also cool. (Bruce will have to get his own blog to present his side of the argument.) I think my favorite space sounds are the ones they make from the radio emissions of pulsars.
Saturn's crescent On January 24, 2006, Cassini's view of Saturn and its moons was of a crescent phase. Part of the night side of the southern hemisphere is very dimly lit by reflected light from Saturn's rings, which are seen edge-on and are practically invisible as a dark line against the sunlit crescent. Credit: NASA / JPL / SSI |
Getting back to the lightning on Saturn story, the thing that really captured my attention about it was that while RPWS can essentially "hear" the emissions, it can't "see" them -- by which I mean that RPWS doesn't know where on (or around) Saturn the emissions were coming from. Based upon the character of the emissions, they suspected that they originated from a giant storm, and they could even say at what longitude on Saturn the storm should be sitting, but they had no way of detecting such a storm. Furthermore, Cassini's point of view on Saturn made it difficult for them to be able to see a storm in Saturn's atmosphere, because these days Cassini is spending most of its time on Saturn's night side. So what was the RPWS team to do to confirm their suspicion?
What they did was send an alert out to ALPO, the Association of Lunar and Planetary Observers, a worldwide club of amateur astronomers. Within hours, the RPWS team release says, they had images of Saturn that clearly showed a storm at the right longitude, from a couple of French observers who had a 12-inch telescope:Amateur observers catch a culprit storm on SaturnTwo amateur observers captured three views of Saturn on the evening of January 25, 2006, from Melun, France through a 12-inch telescope, in the hopes of finding the source of dramatic radio emissions observed by the Radio and Plasma Wave Science instrument on the Cassini Saturn orbiter. They spotted a white storm in the southern hemisphere (top of the image) moving from right to left. The amateur observations complemented Cassini's, because Cassini was primarily viewing the night side of Saturn when the storm was discovered. Credit: Erick Bondoux and Jean-Luc Dauvergne |
People looking at Saturn from Earth have a great view right now, because Saturn is near opposition. I think it's terrific how much amateur observers can still do to support space missions. Actually they can do more and more, because bigger and bigger telescopes with more and more sophisticated tracking systems and cameras are becoming cheaper and cheaper. Go amateurs! Eventually, the Cassini imaging team was able to perform some very tricky image processing and get a view of the same storm on the night side of Saturn, lit by reflected light from Saturn's rings:Lightning-generating storm on the night side of SaturnThe bright spot on this image is a storm in Saturn's atmosphere that appears to be the source of radio emissions detected by Cassini's RPWS instrument on January 27, 2006. The image is of the night side of Saturn; the illumination is provided by reflected light from Saturn's rings, which are out of the field of view to the top. Credit: NASA / JPL / Space Science Institute |
So what's the significance of the storm? The RPWS release says that "the origin of such storms is unknown, but may be related to Saturn's warm interior." That's pretty nonspecific...looks like this is yet another of the reasons to hope that Cassini's mission to Saturn lasts a lot longer than its nominal four years.
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