Tunguska Blast Was a Small Asteroid

malachiorion writes "The Tunguska event, an explosion on June 30, 1908, cleared an 800-sq.-mi. swath of Siberian forest. Was it a UFO crash? An alien weapons test? Now, Sandia National Laboratories has released its own explanation for the Tunguska event. Using supercomputers to create a 3D simulation of the explosion, the Department of Energy-funded nuke lab has determined that Tunguska was, indeed, the explosion of a relatively small asteroid. The simulation videos are well worth checking out — they show a fireball slamming into the earth from the asteroid's air burst. The researchers caution that we should be keeping watch for many more small, potentially earth-impacting asteroids than we are currently tracking."

The Gist

[DrLudicrous]

It seems that while the asteroid itself did not cause as much damage as previously believed (3-5 megatons vs 10-20), the asteroid was most likely much smaller than had been estimated. Too bad the article doesn't give some numbers about the size. Pretty scary thinking about one of these things hitting on top of or near a major population center.

Re:Hmm..

[FredDC]

This one [newscientist.com] they didn't notice until after it nearly missed earth.

So to answer your question: Yes, it's very possible!

Re:"exploding"

[teebob21]

I'll grant you that they do not explode in the traditional TNT/explosives sense of the word. However, falling space debris can indeed "explode" when entering the atmosphere. As they push deeper and deeper and the air gets thicker, it presents more and more resistance on the falling object. Eventually, the wall of air becomes so dense that the action-reaction forces break the falling object up. Violently. Combine that with the fact that the asteroid/comet/meteor and surrounding air has been heated significantly due to friction, and you get a fireball and a tremendous shock wave in the air.

To test this premise, I recommend throwing an egg or three at the front door of your local police station, as hard as you can. You will see that (among other things) the egg does indeed explode.

Re:Hmm..

[teebob21]

Free American English Lesson: Adverbs modify verbs.
Verb in the Subject Sentence: Missed (past tense)
Context: This asteroid was very near to Earth when it missed us.
Adjective: Near (adverb form: nearly)
Thus: The asteroid nearly missed Earth.

Your sentence gets a thumbs up by me!
...Grammar Nazis, please keep walking. :)

Re:Hmm..

[iocat]

Except... if it had nearly missed earth, that would mean that it hit earth, which it didn't.

It nearly HIT earth. The problem with the sentence is the verb, not the construction.

Mirror

[AftanGustur]

The videos total over 56 Megabytes, so I have put up a mirror Here [fransman.fr]

Diameter ~ 50 meters

[Anonymous Coward]

5 megaton TNT = 2e16 J = 0.5 mv^2

Now the typical impact speed of an asteroid is around 20 km/s:

      0.5 m (2e4 m/s)^2 = 2e16 J

      2e8 m (m/s)^2 = 2e16 J,

which yields the mass:

      m = 1e8 kg.

Assuming the average density of the asteroid to be about that of water (1000 kg per cubic meter), we get the volume:

      V = 1e5 m^3

and, assuming a spherical shape, the diameter:

      d = 58 m.

Many known asteroids are somewhat denser than water (1000-4000 kg/m^3).

To get one week's advance warning for the blast, the asteroid must be spotted 10 million kilometers away.

Re:Unlikely to be an asteroid

[dreamchaser]

You're wrong.

One of many references if you'd bothered to look: http://www.physorg.com/news819.html [physorg.com]

Pertinent section:

Expeditions sent to the area in the 1950s and 1960s did find microscopic glass spheres in siftings of the soil. Chemical analysis showed that the spheres contained high proportions of nickel and iridium, which are found in high concentrations in meteorites, and indicated that they were of extraterrestrial origin.

I've seen the 'natural gas' theory before. It's so contrived that it's almost like science-comedy.

Re:Horizon

[Tony Hoyle]

Dammit that almost certainly means it's untrue :p

Horizon is the worst for sensationalising pseudo-science. Many years ago it was a serious science documentary series.. not it's just unwatchable trash.

Re:Hmm..

[tehcyder]

Your sentence gets a thumbs up by me!

...Grammar Nazis, please keep walking. :)

It's grammatically correct, but semantically ludicrous.

What?!

[AJWM]

It appears that most asteroids are conglomerates of shale,

What!? I don't know which planetary system you're from, mate, but since shale is a sedimentary rock (formed by compression of layers of mud, clay and silt beneath a body of water), none of the asteroids in this solar system are composed of it.

Some asteroids may be loosely bound accretions of smaller bodies, but we know for a fact that other asteroids (particularly the bigger ones in the belt) are big enough to melt and differentiate, with metallic cores. Some of those in turn suffered impacts which broke off large chunks of pretty damn solid material. (The Barringer meteorite - a chunk of nickel-iron estimated at 150 feet across - left a mile-wide hole in the Arizona desert.)

Re:A Comet

[dankstick]

The headline on this threw me off too. I recently watched the episode of Carl Sagan's Cosmos that had a segment on the Tunguska Event. He mentioned that there was no crater and that several attempts to find a potentially valuable meteorite were fruitless. The hypothesis was the event was caused by a comet.

I was hoping they found objective evidence for an asteroid, perhaps buried and recovered. Sadly, it is a computer model.

Here is a link to the debate in question...
http://en.wikipedia.org/wiki/Tunguska_event#Asteroid_or_comet.3F [wikipedia.org]

Crater From 1908 Tunguska Blast Found

[tomthegeek]

They found it [slashdot.org]