Tunguska Question

[Schneibster]

Could be. I'm aware that it's (roughly speaking) an exponential dropoff. Of course what this means is that at any given altitude, there will only be a fixed percentage difference in pressure between that altitude and a fixed distance above that. 187 meters is something like a 2.5% difference--seems small to me.

2.5% of a small difference is smaller than 2.5% of a big difference.

Neat. Might I ask specifically what your definition of "bolide" is? I've found several of them on the 'net, including one that only includes impactors.

A bolide is an unusually bright meteor that leaves a trail.

I thought it was much lower than that--5-10 km, not 30 km or more?

That's the bottom of the stratosphere, not the top. The top is at 30-50km. That's even a bit low for the bottom; it's at 8-17km. It sounds like you're talking about the tropopause.

Well, I will happily grant that if the heating occurs within tens of milliseconds, then you indeed should expect some rather energetic EM radiation, including X-rays.

We are in agreement, then.

I am still not entirely convinced that this would happen for a 30 m object, but this opinion is largely based on my ignorance of hypervelocity objects in the atmosphere. Perhaps sometime I will write a simple simulation that shows the balance between radiation and aerodynamic heating.

- Dr. Trintignant

Consider a re-entering spacecraft, which loses contact with the ground because it is surrounded by ionized gas. This is because of the heat of atmospheric friction, and that's in the ionosphere, not even in the stratosphere.

 

[Soapy Sam]

17km/s is the average velocity of asteroids with respect to Earth. Comets have higher average velocities- 40 to 70km/s. But we're talking about asteroids.

Thanks

 

[Dr. Trintignant]

2.5% of a small difference is smaller than 2.5% of a big difference.

But we're talking about a rate of heating here. Now there are certainly threshold values relating to temperatures of vaporization and such, but speaking purely in terms of absorbed energy, there's no wall.

That's the bottom of the stratosphere, not the top. The top is at 30-50km. That's even a bit low for the bottom; it's at 8-17km. It sounds like you're talking about the tropopause.

No; what I meant was that I thought the Tunguska body exploded at 5-10 km. Which I guess would put it in the tropopause. I suppose there could be a significant difference between the altitude where it heated and where it exploded, but that would also mean significant time for the heat to radiate away. Have you read any papers detailing the difference here? I see that the Sandia simulations have explosions that start as high as 20 km and continue down to 8 km.

Consider a re-entering spacecraft, which loses contact with the ground because it is surrounded by ionized gas. This is because of the heat of atmospheric friction, and that's in the ionosphere, not even in the stratosphere.

But that's a pretty low temperature, compared to what we're talking about--it's only thousands of kelvin. Remember again that radiative power is proportional to the fourth power of temperature. My plausibility argument--if it works at all--doesn't work for temperatures as "low" as 100,000 K, let alone 10,000 K or less.

- Dr. Trintignant

 

[Damien Evans]

There is some suggestion that it may have been an antimatter particle. Specifically: this would explain locally elevated gamma radiation.

If it was, I would think it would have annihilated higher up in the atmosphere than it did.

 

[rsaavedra]

The folks who play in this area are basically saying they think that the material that splashed up from the impact site re-entered the atmosphere a few minutes to an hour later and raised the temperature of the sky to a few hundred degrees pretty much everywhere on Earth. This basically broiled anything not under water or underground alive immediately, and triggered world-wide forest fires. A toasty day indeed.

To think of material "splashing up" into space, then coming back into the Earth's atmosphere a few minutes to an hour later! As if the planet was just a little pond. And bringing the temperature of the entire atmosphere everywhere on Earth up to a few hundred degrees?!!! Gee... Talk about an event beyond our little human scale. Humbling.

 

[Soapy Sam]

There's a small town in Germany, named Nordlingen.

Near the town are quarries. The rock has some odd mechanical properties, not least of which is that it's upside-down. There is no tectonic reason for this.
In fact, the quarries are part of an eroded crater rim, where the ejecta effectively splashed out like those high speed photos of a milk drop falling into coffee.

Rock deforms as a plastic (and even a fluid), if the strain rate is very, very low (eg deformations of mm per century) especially if you warm it a bit and percolate water through it. This is demonstrated in mountains and canyons the world over. What was not appreciated till this century is that if you hit rocks incredibly hard , extremely fast, much the same happens. Only instantly.