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On 03/23/2013 09:50 AM, Bernard Cleyet wrote:
"In the anacoustic zone above 160 kilometres (99 mi), the density is
so low that molecular interactions are too infrequent to permit the
transmission of sound."
http://en.wikipedia.org/wiki/Thermosphere
That rather depends on the wavelength. The physics here is easy
to understand: Sound is grossly attenuated unless the wavelength
is long compared to the mean-free-path in the medium.
Note that the wikipedia is inconsistent with itself:
"the speed of sound (in the interstellar medium) is about 100 km/s. "
http://en.wikipedia.org/wiki/Heliosphere
Sound travels far better in the interplanetary medium, which is
far denser than the interstellar medium.
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