# Meteor explosions

1. Mar 7, 2015

### thetexan

I'm watching a show on meteor catastrophes.

They can cause damage by hitting the earth causing a mechanical explosion due to the energy of the mass transferring into the earth as kinetic energy.

What I don't understand is what makes them explode above the
surface like Tunguska?

Tex

2. Mar 7, 2015

Staff Emeritus
Hitting air at a zillion miles an hour is like hitting a brick wall.

3. Mar 7, 2015

### Staff: Mentor

Perhaps, but that probably doesn't help the OP understand the physical mechanisms underlying the explosion.

4. Mar 7, 2015

5. Mar 7, 2015

### davenn

Grrrr that video is blocked from being viewed in Australia and maybe other countries

HI Tex ....

The difference between an object exploding/vaporising in the atmosphere, Tunguska, or hitting the ground and producing a crater like the Arizona
Meteor Crater, is mainly composition. Lower density stony ( including ice/stone composition of comets) will break up and disintegrate easier in the atmosphere.
Where as the very solid nickel/iron ones are much more likely to punch through the atmosphere. They will/can still loose up to around up to half their mass
during their passage through the atmosphere

here's one good article
http://www.britannica.com/EBchecked...nd-meteoroid/258997/Basic-features-of-meteors

cheers
Dave

6. Mar 7, 2015

### OmCheeto

My guess is that "explosion" is a poor word for what happens.

From wiki:
I would describe it more like a powerful, extended, disintegration. It sounds like the Tunguska event took 7 to 8 minutes.

The whole thing is powered by the kinetic energy of the meteor/comet. It heats up due to air friction.

Here's an interesting comparison:

I've actually been doing a bunch of meteorite energy calculations for about a week, since I found a meteor simulator. Mostly, I've discovered that I don't know how to do math, but that's besides the point. For your problem, we just need a few numbers, and some simple algebra to see what's going on.

From the above shuttle example, we get 3.23e12 joules. From my work, I know that there are 4.2e9 joules in a ton of TNT.
Simple math: The shuttle has to dissipate the equivalent explosive energy of 775 tons of TNT, in about 30 minutes.
Or about 26 tons of TNT each minute.
Roughly half a ton per second.

The shuttles were designed to do it. Asteroids, are not.

ps. I've never seen a TNT explosion. I tried to find an appropriate video, but they were mostly annoying.

Last edited by a moderator: May 7, 2017
7. Mar 8, 2015

### D H

Staff Emeritus
My guess is that "explosion" is an extremely good word for what happens. It's not just my guess. It's the guess of many, many scientists.

That was overly selective copying, Om. There were other reports that indicated it was indeed an explosion.

Eyewitness accounts are not the most reliable. This is particularly so with respect to calamitous events. People's recollection of what happened is anything but perfect, and their sense of time can get quite skewed. You are relying on accounts of very scared people to make your claim.

Moreover, you are confusing the duration of the explosion with the duration of the consequences of the explosion. The explosion created shock waves that flattened trees across 50 or more kilometers. People somewhat removed from the explosion would have first seen the explosion, then experienced the shock wave, and then heard the sound of 80 million trees being blown down. These events would not have occurred simultaneously. They would instead have been spread across a few minutes. The scariness of this easily accounts for the perceived eight minute long event.

The Tunguska meteor most likely was a rubble pile asteroid, a collection of boulders, rocks, pebbles, and dust weakly held together by gravity that hit the top of the atmosphere at over ten kilometers per second. Not much happened when it first hit the top of the atmosphere. The atmosphere gets exponentially more dense as altitude decreases. The asteroid would have been shaking and losing pieces at an exponentially increasing rate, with the exponential time scale on the order of seconds to tens of seconds.

An even more rapid exponential process kicked in when it got to an altitude of ten kilometers or so. Rubble piles are not one single solid chunk of rock. They instead comprise a very large number of little pieces of material held together weakly by the asteroid's gravity. They can be broken up other forces. That's exactly what happened, and it happened very quickly.

The atmospheric drag force on an object is proportional to the product of the atmospheric dynamic pressure, the object's cross section area to the wind, and and its kinetic energy. The onset of the breakup of the asteroid made the area increased drastically. Some of this increased energy release went back into the asteroid, which acted to increase the rate at which the asteroid was disintegrating. This is a exponentially increasing positive feedback loop. While psychological positive feedback is a thing to receive, positive feedback in physics never results in anything good. Another name for exponentially increasing positive feedback with a sub-second exponential factor is "explosion". In this case, the Tunguska event released the equivalent of about 1,000 Hiroshima bombs in a few seconds' time. Another name for that is a massive explosion.

8. Mar 9, 2015

### Ophiolite

This is a very technical look at the issue, but it is current and worth a look.

Grigoryan, S.S. et al "Physical Mechanism of Chelyabinsk Superbolide Explosion" Solar System Research, 2013, Vol. 47, No. 4, pp. 268–274

Abstract
The work presents modern ideas on the physical mechanism of explosion of large meteoroids (superbolides) in the Earth’s atmosphere at the end of their trajectories. As a result of our work, the values of following parameters were obtained: the altitude of the beginning of the aerodynamic destruction of a meteoroid like the Chelyabinsk superbolide; the altitude of a relatively very thin layer, characterized by sharp aerodynamic deceleration of a fragmenting and laterally expanding space object, accompanied by an impulse transformation of kinetic energy into thermal energy with plasma generation which results in intense electromagnetic radiation and an explosive shock wave; and, the initial temperature of such a plasma.

9. Mar 12, 2015

### OmCheeto

At my first science forum, back in the late 90's, they would annotate such posts of mine with; (this is nonsense...moderator)
How on Earth, my brain left out the fact that 2000 km^2 of forrest were flattened, is beyond me.

I think my motive in the selection was to get as distant an eyewitness account as possible. People close to the epicenter seemed to be, metaphorically speaking, "inside the car" during the crash.

As part of my penance, for sharing such nonsense, I've spent the last 3 days gathering data, and skimming multi-hundred pages papers, in an attempt to make sense, of what you obviously understand.

About the only thing I concluded, was that the Tunguska event, is very peculiar, and worthy of the ≈1000 papers written about it.

"44,500 °F", is a lot.

One of the papers I looked at:

Lots of incomprehensible maths, and the chapter titles gave me an indication of how complex (ie. above my head) this problem was.
Reflection of Blast Wave, Altitude Effect, etc.
High Temperature Opacity of Air
The Equation of State of Air Below 25,000°K

The most peculiar thing, was that when I plugged in the numbers from the NASA article above, into Purdue's "Impact: Earth!" simulator, the resulting numbers, don't match what happened.

I suspect, we'll be discussing the Тунгусский Феномен, for quite awhile.