Slashdot Mirror
Eerie Sounds from Saturn
Mick Ohrberg writes "Scientists at NASA have now heard proof (called 'Saturn kilometric radiation') that Saturn has a phenomenon similar to the earths' Northern Lights (aurora borealis). Talking about the eerie sounding noise, Dr. Bill Kurth with the University of Iowa, says "We believe that the changing frequencies are related to tiny radio sources moving up and down along Saturn's magnetic field lines."
It couldn't sound any spookier if they added a Theremin."
Sounds like some of the effects from the soundtrack to Forbidden Planet!
http://imdb.com/title/tt0049223/
As someone who's had a minor career in computer music, I've seen this type of thing again and again. You can take almost any sampled data and if it is something other than purely random you can massage the frequency response into the human hearing range. Its fun to do, but it usually doesn't tell you much.
In the original version of 2001, they had Saturn instead of Jupiter as the source of the Big Mystery. Clarke thought it was an "interesting coincidence" that Saturn's rings supposedly formed at about the same time the first humans evolved. (Can't verify whether that's accurate, and am dubious as to the meaning of "coincidence" at that time scale.) The extra difficulty of doing SFX with the rings was just a little bit too much, and they changed it to Jupiter. If they'd stuck with Saturn, imagine the silly comments that this discussion would have!
Question: at what level of vacuum does sound cease to propagate? I imagine "cease to propagate" might be subjective? Or perhaps there's a definite line like "when the mean free path of the gas molecules is large compared to the chamber dimensions" (a gas molecule hits the wall more often than it hits another gas molecule) (as in turbopumps, is that even correct?)... though what that would mean in outer space isn't clear to me.
At very low pressures such as the high altitudes of commercial flight routes you still obviuosly have significant propagation, I think that the limit is more theoretical than anything. I think you are in a good path with your reasoning, as the wavelength of a sound wave is the distance between 2 peaks of high pressure, which has a low pressure valley in between, in an extremely rarified environment, such as in deep space, the extremely large mean free path of the molecules would result in mind numbing wavelengths, and unsignificantly low frequencies. I leave the numerical exercise to the experts!