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Because of the lack of any materials to propagate sound, it can't spread in space. There's the air in the atmosphere, but its volume mass increases constantly (either linear or exponential, I don't know) - it means that atmosphere doesn't have a sharp edge that separates it from space directly.

What happens, when an asteroid moves faster than the speed of sound (I suggest it happens quite often, but I'm not sure) and it enters to the atmosphere of Earth?

Does it create a sonic boom? Definitely, what's the level of atmospheric pressure that is necessary to the exist of sound (and consequently, sonic bangs) and how far is it from Earth surface?

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    $\begingroup$ Here is the recent asteroid that fell in Russia youtube.com/watch?v=xSDx3NyGtXc .second take youtube.com/watch?v=P7eDpMNQU6A $\endgroup$ – anna v Jul 30 '13 at 11:51
  • $\begingroup$ This answer must mean "yes" =) but I still don't get, why it doesn't happen yet in upper parts of the atmosphere? Those also have some air, even if its pressure is very low. (almost zero) Is there an exact value of air pressure that is necessary for sonic bang? $\endgroup$ – Zoltán Schmidt Jul 30 '13 at 12:02
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    $\begingroup$ It is a qualitative answer, not a quantitative one, that is why it is a comment and not an answer. It is not a simple problem and it is not in my field. Have a look at en.wikipedia.org/wiki/… . $\endgroup$ – anna v Jul 30 '13 at 13:56
  • $\begingroup$ @ZoltánSchmidt it is quite an interesting process too $\endgroup$ – user36538 Jan 12 '14 at 23:12
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According to the American Meteor Society, the sonic boom of an asteroid or meteor (sometimes referred to as a 'fireball') is due to

If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km (30 miles), and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon.

And from CalTech's CoolCosmos page

When an object travels faster than the speed of sound in Earth's atmosphere, a shock wave can be created that can be heard as a sonic boom.

The reason for asteroids causing sonic booms in the lower atmosphere, is according to the article How the Falling Meteor Packed a Sonic Punch (Klotz, 2013) is due to

Because the meteor is supersonic, the waves, which travel at the speed of sound, can’t get out of the way fast enough. The waves build up, compress and eventually become a single shock wave moving at the speed of sound.

Looking a bit further in to what a sonic boom (Using a jet as an example) is and how it occurs is illustrated in the following diagram

enter image description here

Image source

So, if a meteor, asteroid is going faster than the speed of sound for particular part of the atmosphere, then a sonic boom will occur. Going back to the American Meteor Society's description of the likely cause of a sonic boom, they stated that if a meteor comes in

below an altitude of about 50 km (30 miles)

then a sonic boom is likely to occur, one of the reasons is that the speed of sound is slower, due to the temperature of the atmosphere at that height and lower. Below is a graph showing the speed of sound plotted against temperature as a function of atmospheric elevation:

enter image description here

Image source.

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I was looking this up to see how common sonic books from meteors uccur. I was on my roof two nights ago finishing up a project after dark. A light caught my eye. As soon as I looked up I herd a boom right as a meteor shot derectly over my head. It was a red and white streak from north to south. It was huge for a shooting star. The boom came from the direction of the meteor. I live in San Diego so if it made it through it probably hit Baja Mex or the Pacific. I for one can confirm meteors create sonic booms.

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