They keep saying "explosion" but was there actually one? There was a sonic boom, and the rock disintegrated in the atmosphere, but I've not seen any evidence that it exploded all at once.
EDIT: well, lots of news agencies are using the word "exploded", so maybe it did. I see somebody else mentioned claims that Russians shot at it, but I'm skeptical that they'd be able to notice and react to this thing in time.
EDIT EDIT: OK so it looks like space rocks "airbursting" is not unheard of: [0]. Really curious what the physics of that involves.
Is is not an oxidized detonation explosion in the traditional sense, it's a hypersonic solid-gas fragmentation impact.
In this case, the most intense period involves peak pressure. The meteor falls down, encountering gradually thicker air, heating up and heating up, until finally, the pressure and differential internal stresses are sufficient to separate it into smaller pieces.
These smaller pieces are a lot less massive per surface area, so the pressure acting on them is going to be a lot more relative to their mass, and they are going to slow down much faster. The deceleration while this is going on, then, is going to induce sufficient turbulence to break them up even faster. So the breakup occurs in a sort of chain reaction, and the pressure waves from nearby fragments influence each other, adding turbulence and slowing the cloud of fragments further, until it all ends up as small particles spread over a large area. These particles are moving for the first fraction of a second of their life at supersonic velocities, generating a very large pocket of vacuum / shockwave as they dissipate their energies. The rapid expansion of the largest highly vulnerable layer of the asteroid into a cloud of dust thus constitutes an 'explosion', even if the energy is all kinetic instead of the slow chemical burning that happens afterwards as the white-hot particles oxidise & turn to ash.
Asteroids are not uniform, however. Wrap a chunk of granite in a chunk of sandstone, and you may end up chipping off bits of the sandstone for 10s, heating up until all the white-hot sandstone flies off in fragments at once for 2s, and then the granite flying further towards the ground until its yield strength is exceeded in a higher pressure regime, or it impacts the ground. With complex structures, multiple waves of fragmentation are possible, and rather than being a simple matter of the fragments immediately dissipating into small particles and a harder core, a meteor will tend to split into chunks which themselves become smaller examples of this phenomena.
Refreshingly honest. And that's probably true for the planet, not just for Russia. You can bet there will be a lot of people using this incident to try to get funding so they can go play while pretending they are going to save the planet at some unspecified future date.
EDIT: Just saw Bill Nye explain this on the DA14 webcast from planetary.org. When the meteor hits the atmosphere at such a high velocity, it's like hitting a brick wall and it explodes on impact. Then the shock wave propagates to the ground as the fragments fall and oxidize.
IIRC, the meteor can also explode due to the core heating up from the atmospheric friction, though this depends on the make-up (materials, density, configuration) of the meteor.
EDIT: well, lots of news agencies are using the word "exploded", so maybe it did. I see somebody else mentioned claims that Russians shot at it, but I'm skeptical that they'd be able to notice and react to this thing in time.
EDIT EDIT: OK so it looks like space rocks "airbursting" is not unheard of: [0]. Really curious what the physics of that involves.
[0] http://en.wikipedia.org/wiki/Tunguska_blast#Asteroid_airburs...