Hello,
This meteorite above Russia apparently exploded with a power 30 times stronger than the Hiroshima nuclear bomb.
I understand that it gets hot from entering the atmosphere, and is quite big with a mass of 10000 tons, but still, it existed out of stone and iron, how can such "passive" material create such a huge explosion?
Also, it went at 15 km/s and exploded 30km above ground. If it exploded 2 seconds later it would have hit the ground. How likely was that?
Thanks!
Very likely, as you can tell from the fact that no civilization we know of has been wiped off the planet during the last 6,000 years. Besides, 2 seconds are an eternity at such a speed, it's not like two seconds before impact are anywhere "near the ground".Also, it went at 15 km/s and exploded 30km above ground. If it exploded 2 seconds later it would have hit the ground. How likely was that?
The Tunguska event exploded at 5-10km, with the power of 1000x Hiroshima's (sad that that's a unit of energy now)... and would've taken out a city had it have hit one, rather than Siberian forest (it levelled a 46km * 46km area of trees). So, these things are definately capable of doing a lot of damage.
Apparently, kiloton-equivalent air-bursts occur in the upper atmosphere (at safe altitudes) around once per year!
Interestingly, this 2013 meteor is apparently a "once in 100 years event", and Tunguska (a megaton-level event) was roughly 100 years ago, so it was fairly on time 
I'm not sure about how the explosions occur, but like with anything moving extremely fast through the atmosphere, the increase in pressure in front of the object generates a hell of a lot of heat. I've had a stone barbecue crack and fire out bits of shrapnel explosively due to heating just from a wood fire, so I can imagine that with enough heat you could explosively vaporize a giant rock...
A Russian meteor could conceivably explode if it was a Korean nuclear long range missle test, or if it was a telecommunication sattelite from the Cold War equipped with half a dozen missles coming down. You don't really know what it was, do you.
Care for Occam's razor?
If you take a frozen mug and pour hot coffee in it, it can explode pretty dramatically, and glass or ceramic are two of the most "passive" materials there are. It's all about temperature change causing uneven expansion. Cold meteorite burning up in the atmosphere is the same kind of temperature change.
My understanding is that the meteor exploded because it essentially 'hit' the atmosphere. At the high speeds at which it was moving, hitting the atmosphere must be more like a brick wall than gently passing through it.
I don't think heat had much to do with it - though I don't dispute that there's a lot of heat buildup due to the pressurized air. I've read somewhere that most meteorites that fall to earth are still frozen, mostly because the short entry time (usually in matter of seconds) doesn't leave enough time for the core to be heated up at all - the rules of convection still apply - heat only spread so fast.
You don't really know what it was, do you
We kinda do. There's the lot of amateur videos posted online, the analysis of scientists of the explosion and the readings that were taken by various instruments around the world. I seriously doubt it was anything other than a meteor.
Occam's razor is applicable most of the time, but that's also its danger. Or rather, it's always applicable, but it's not always right. The apparent likely cause is not necessarily the only possible one, and not necessarily the correct one.Care for Occam's razor?
As far as I remember from physics Milcho is right - atmosphere at that speed is like hitting brick wall.
According to report from NASA the object had diameter of maximally 17 m, mass around 10000 tonnes (a really heavy one, because their density is often less than water density) and velocity 17900 m/s. Kinetic energy of this object is 1602050000000000 J = 1602 TJ. Energy equivalent (in TNT) of this kinetic energy value is around 383 kTons of TNT - e.g. we need at least 383 kTons of TNT equivalent energy to just stop the motion of the meteorite. Assuming that energy of explosion must be higher than just kinetic energy (it's calculated using the thermodynamic energy of detonation) - we could get somewhere to 500 kTons.
I'd say it's extremely likely to be a meteor, considering the number of independent observations, and the world wide consensus among astronomers that it was....maybe it was a NK missile...
An 'explosion' is a rapid thermal reaction with rapid expansion. Rapid expansion often results in the loss of structural integrity.
How could dynamite "explode"? Well, a rapid oxidation reaction takes place in the substance, resulting in an endothermic expansion that transfers its energy into the surrounding substrate (which could be, say, rock in a mine or a railroad trestle in front of an oncoming mail train). A great deal of force can be imparted by this rapid endothermic reaction. Newton's third law state the force of a reaction is proportional to the mass involved and the acceleration, and the acceleration of the products of reaction is very high indeed. This expansion takes fractions of a second.
So, how could an object colliding with a gas at very high velocity explode? Well, chances are goof that this particular meteorite was a type called a 'carbonaceous chondrite' which tends to lack structural cohesiveness. As it hits the atmosphere at a great velocity, a couple of things happen. The outer layers heat very rapidly due to friction with the (rather thin upper) atmosphere, heating in an exothermic reaction, and an oxidative reaction begins between the exposed carbon and the free oxygen in Earth's corrosive atmosphere, and endothermic reaction. A great deal of heat causes the chondrite to expand rapidly and lose its structural integrity this exposes more surface area to the axidation reaction, which causes still further exothermic reaction, until a critical mass is reached and the entire object expands very rapidly. This can take mere seconds.
So that is how a meteorite such as the one over Russia the other day can "explode": a rapid thermal expansion causes the loss of integrity of the object. It is, indeed, rocket science.
And that's the problem: You would hardly ever hear it in the news if it was anything else but a meteor, not in any part of the world, but especially when it happened in Russia -- they'd never admit to that.
In the age of Youtube, Facebook, and all the other crap...
It couldn't be much else than a meteor. The height of the explosion can be quite easily determined (from the latency of the sonic boom). Knowing the height, it's not so hard to determine the speed from the videos (so one could fairly easily make one's own calculations and estimations to verify the meteor theory even without any instruments, like satellite images of the event, or the cloud that was left behind).
Not anything that humans built are big enough to leave a 400 km long (and pretty thick) smoke (and I guess jet stream) trail with that speed at that height.
Plus the whole thing looks just the same as bigger falling start everyone of us probably have seen (with the explosion at the end). This was only bigger.
