I have just been re-reading the 1977 book by Rupert Furneaux about the massive explosion that occured in the Tunguska region of Siberia in 1908. The book does not come to any firm conclusion of the cause although a meteorite is probably the main suspect. Does anyone know what the latest thinking on this is?. I have tried Google but what information there is seems to have been hijacked by the UFO brigade. Snopes does not have any info either. So what did cause the explosion?
Meteorite is still the top contender, with some competition from “a chunk of Encke (sp?).”
Meteorite or comet is what I’ve seen on the documentaries. The peculiar pattern of downed trees fit that produced by the airburst pattern one of these would have caused.
Extensive searches were carried out at least twice to find some remnant of the extra-terrestrial object, but to my knowledge none was ever found.
I thought it was a Tesla experiment gone wrong?
I’ll get me tinfoil coat and hat.
Well, that’s what he told Spider, when he discussed it with him at Lady Sally’s place 40-odd years after his death, but don’t let that influence your firm grasp of reality! 
I thought the problem with the meteor theory was the lack of impact crater as well as any traces of the expected meteoritic rock & iron at ground zero. A chunk of ice (comet) would have had the same affect but not leave a crater and no rocky fragments. So comet seems more likely unless some new information has surface since I last read about this 15 years ago.
Furneaux 's is probably the best book I’ve read by someone who hasn’t been there. Overall the best books are Yevgeny L. Krinov’s books The Principles of Meteorics and Giant Meteorites, both of them published in English by Pergamon Press. Krinov has the distinction of having been there with Leonid Alekseyevich Kulik, who first scientifically studied the site. But his books are even earlier than Furneaux’s
The Tunguska event is interesting in the way it acts like a Rorschach test – anyone who investigates it seems to see whatever exotic astrophysical object he wants to see in it – ricocheting meteors, clouds of dust, antimatter (three different groups proposed this), quantum black holes, cometary nuclei, etc.
For a long time the chief theory was that it was a fragment of the head of a comet (only I thought it was Pons-Winnecke, not Encke). There was an infusion of a lot of dust high in the atmosphere at the time, causing “noctilucent clouds” that lit up the skies of Europe. And it’s rarely mentioned, but another meteorite fell at the same time as the Ungus object, a pretty good distance away.
Recently, though, I’ve been hearing that the Tungus object might be an ordinary meteorite that simply vaporized in the atmosphere. For my part, I still like the cometary hypothesis – whatever it was exploded in midair, and didn’t impact the earth. That would be quite a trick with a solid body to get just right. But I can see a “dirty iceball”, especially one loaded with volatile frozen compounds, breaking up before it hit the earth. For the record, the 1959-60 expeditions found plenty of micrometeorites of both metallic and stony type, all melted and frozen into microspheres, apparently by the heat of atmospheric friction and/or the explosion. Even Kulik may have found a solid piece (it’s in one of his last reports from the site – his reports have been translated into English and reprinted in the journals Popular Astronomy and in the Izvestiya Akad. Nauk. SSSR, if you want to look them up.)
Yes, exactly. Whatever it was, it was probably travelling on the order of 150,000 miles an hour or about 42 miles a second. This means that the object lasted in the atmosphere for about two seconds. The blast height itself was pretty low so if the object had survived another .02 seconds or so, it would have left a crater.
And whence this figure of 42 miles/sec ? I’ve never seen an accurate velocity figure, and don’t even know how one can be derived, so that 0.02 sec seems even more squirrely.
One of the few velocity figures I’ve seen seemed to be derived by assuming that the object must have been extra-solar, and was arrived at by adding the escape velocity of the solar system to the surface rotation of the earth – not a very precise way of arriving at a figure.
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From here.
I think it’s pretty reasonable to analogize whatever it was, whether comet or meteor, to the Leonids – they have an orbit inside Uranus, though they’re significantly faster than most meteors because they’re retrograde. Whatever it was, it was almost certainly crossing earth’s orbit at a sharp angle so its relative velocity would be on the order of at least 20 miles/s.
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It sure isn’t. Why would you use the speed of surface rotaton of the earth? 
It might make some sense to use the orbital speed of the earth which is about 18 miles/sec.
When I say orbital speed, I mean the speed that the earth is orbiting the sun.
From “order of 150,000 miles per hour” to “42 miles per second” is a leap from the rough to the exact that annoys me. Especially when you throw that “0.2 seconds” n.
And I’ve never heard anyone claim that the Tunguska object was related to the Leonids.
All the calculations about energy/mass/velocity I’ve seen have been pretty rough, based on assumptions about the overall energy (comparison to the atomic bomb) or assumed wave amplitude (based on microbarometer recordings) or estimates of speed from visual sightings, something like that. Nailing down a real velocity isn’t possible . It really does seem to me a remarkable coincidence that the object would have had just the right amount of energy to explode in the air, but not to make it to th earth. It seems far more likely that there wasn’t much metal r stony material there to start off with.
Fame and fortune await, Rayne Man’s question has been tackled by Cecil in this week’s column: What was The Tungus Event?
But they both have the same number of significant figures.
The .2 seconds was based upon the calculated total flight time of 2 seconds. I’m not even sure if they’re accurate, but it would seem close.
No, it happened in June. But I think Truth Seeker was just trying to use a “typical” meteor speed.
Cecil has just published a column answering the OP directly:
http://www.straightdope.com/columns/030228.html
A far-out possibility is the strangelet, or strange quark nugget. One (or two) may have hit the Earth in 1993
although the impact site in these cases is supposed to experience relatively little damage.
Dopers are going to hate this - as I cannot recall the detail - but I think Eburancum45’s post is near to one of the two chief likely causes that were the conclusion of a BBC or Channel 4 doc on this incident a few years ago:
No 1. was still I think the comet theory.
No.2 was the a tiny piece of “antimatter” struck the Earth. Now I do not know or at least recall enough to elaborate but leave to other if this secondary possibility links in with “strangelets” or “strange quarks” or they make up a No.3 theory…
So I guess Cecil needs a forum he can post in called “Comments on General Questions”.
Another left-field candidate is a chunk of mirror matter. Not as out there as death-rays, but the theory isn’t exactly mainstream - unless anyone wants to head out to Siberia with some shovels and a centrifuge and actually look for the stuff.