Meteors exploding in mid air

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Why and how do meteors explode in mid air?
There have been many notorious cases, both in recent history as well as in the more distant past, of meteors exploding in mid air, sometimes causing vast amounts of damage (or, in more minor cases, breaking windows etc). For example the so-called Tunguska Event is attributed to an air burst of a meteor, releasing energy in the megaton range.

Could someone explain the mechanics of how exactly a meteor can explode in mid air, releasing that much explosive energy? I can't even begin to imagine how or why that happens.

I do understand that objects moving at extremely high speed (such as meteors, or re-entering space capsules) experience extremely high temperatures due to them compressing the air in front of them (which causes that air to become extremely hot), but I don't really understand how this could cause the meteor to not only suddenly explode, but to do so with such great force that it may even cause an explosion in the megaton range.
 

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  • #2
Nugatory
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Could someone explain the mechanics of how exactly a meteor can explode in mid air, releasing that much explosive energy
Loosely speaking, an explosion happens when a large amount of energy is released in a small volume of space very quickly. The matter in that volume (generally whatever is exploding and the air around it) is vaporized and expands rapidly and forcefully, producing the explosion.

A meteoroid can carry an enormous amount of kinetic energy. For example, the kinetic energy of a one kilogram object moving at 50 kilometers/sec is more than 1000 megajoules (but don’t take my word for it! Do some calculations of your own, the formula for kinetic energy is ##E_k=mv^2/2##, and you might try it with reasonable estimates of the size and speed of the Tunguska object), roughly equal to the energy released by a quarter-ton of TNT.

A large solid object may punch through the atmosphere and it will stop dead when it hits the surface; all that kinetic energy will be converted to heat immediately and there’s an explosion. A less solid object will break up and vaporize in the air, and again all that kinetic energy is released as heat at once.
 
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  • #3
phinds
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What research have you done so far? What have you found out? A 3-second internet search gave me the answer so it shouldn't be too hard.

EDIT: Ah, I see nugatory has already provided you /w the answer. What he's describing is called the "parachute effect"
 
  • #4
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For example, the kinetic energy of a one kilogram object at moving at 50 kilometers/sec is more than 1000 megajoules ... TNT.
TNT is 4 MJ/kg; i.e., the "kinetic" of/in the term "kinetic kill."
 
  • #5
Warp
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A large solid object may punch through the atmosphere and it will stop dead when it hits the surface; all that kinetic energy will be converted to heat immediately and there’s an explosion. A less solid object will break up and vaporize in the air, and again all that kinetic energy is released as heat at once.
I don't really understand why the object breaking up in mid-air causes it to release more energy than if it doesn't break up.

Is it because if you break up an object into smaller parts, its total surface area will increase, even if its total volume (and thus mass) stays the same? And with a larger surface area it will push against that much more air (which in turn may heat it so much more, breaking it up even further, effectively causing an accelerating runaway chain reaction)?

If that's the correct answer, it would actually make sense.
 
  • #6
phinds
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Is it because if you break up an object into smaller parts, its total surface area will increase, even if its total volume (and thus mass) stays the same? And with a larger surface area it will push against that much more air (which in turn may heat it so much more, breaking it up even further, effectively causing an accelerating runaway chain reaction)?
Exactly. That is the "parachute effect" that I mentioned in post #3
 
  • #7
jim mcnamara
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Consider basic stuff:
During WWII, some types of bombs were set to explode before impact. The case of nuclear weapons is an example.

The Hiroshima bomb was exploded at a height of 580 meters (1,870 ft.) for maximum effect. The bomb’s explosive force then shot directly down to Earth below (ground zero), spread swiftly out to surrounding hills, and then rebounded back into the city. A house-top weathervane was later found pointing toward the city center, a witness to the rebounding force.
--- http://atomicbombmuseum.org/1_overview.shtml

So wouldn't the same apply to an exploding meteor?
 
  • #8
Nugatory
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So wouldn't the same apply to an exploding meteor?
It does. In general an explosion in the air creates overpressures over a much larger area than the same explosion on the ground, while the ground explosion delivers higher pressures to a smaller area. (This is why hardened point targets like underground bunkers are attacked with ground-burst weapons while dispersed soft targets like cities are attacked with air-burst weapons).

But here I think that the original question is not about the destructive effects of a meteoroid explosion in the air as opposed to on the ground, but rather about how the explosion in the air can happen at all. And the answer to that is, basically the same as if the meteoroid were to hit the ground: When the meteoroid stops, all of its kinetic energy is more or less instantly released as heat. A solid meteoroid that doesn't break up will be stopped by the ground; but if it disintegrates into small particles, dust, and vapor then the air will stop it.
 
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