Asteroid

which do you think caused the Tunguska explosion in Siberia in 1908?

A large broken up meteorite… ( I think??! )

Such as the Tunguska blast caused by a meteror or comet streaking across the Siberian sky?
In response to nick, I add this to the question, "Why are objects are far more likely to enter at a shallow angle relative to the ground than a large one?"

It’s simply perspective.

If you are watching someone throw a baseball or cricket ball, unless he throws it straight at you, it will move in a path acroos your field of vision. If it was a flaming ball and you were watching him at night, they would make a visible path, just as meteors do.

I have seen a meteor strike head-on, and it just makes a small explosion in one spot – no trail.

The vast majority are not going to come straight at you, just by the law of averages. All those will appear to leave a trail

Your question:

I think I know what you are asking. The fact is that meteors move so fast that even if they come in only 10 deg off directly towards you, they will produce a fast streak. However, in general, if it make a shorter streak, it is probably a very steep angle; if it produces a long streak, it is probably a shallow angle.

I don’t know if the angle of strike is anything other than random. Larger meteoroids have been seen to go straight through the atmosphere at a very shallow angle, and off into space again.

That is a scenario that Apollo asronuats returning from the moon faced. Come in too steep and you burn up; come in too shallow and you bounce of the atmosphere into space and never come back. Apollo 13 was particularly tricky as they had to manually guide the moon lander which was never meant for that purpose.

Science has moved on since the events in the Siberian Tunguska on June 30th 1908 but this story still holds a facination. A Comet fragment makes sense to me but what do you think. Makes you wonder If there are any more Comet fragments out there?
On June 30th 1908 a fiery object was seen streaking over the heavly forested and mostly deserted Tunguska region of Siberia. The object detonated with the power of a small nucliar explosion flattening trees for a radius of approx 30km and leaving the now familiar telegrapg pole trees below the epicentre. This object is now believed to have been a Comet fragment that, passing through the atmophere, became superheated and detonated at an altitude of 6 to 8 miles. We hear much in the news about close encounters with asteroids but what about Comet fragments. They are not all shooting stars!

Never read it. Based on the modeling that surrounded the Shoemaker-Levy impacts on Jupiter back in 1994, a comet fragment makes even more sense than ever. Comets appear to be made of fluffy enough stuff to splatter on an atmosphere without penetrating far. A full sized intact cometary nuclei would deliver some chunks to the surface of the Earth. Anything much smaller than 1 km would not. (see first source)

There was a big controversy over whether smaller cometary fragments are still bombarding the earth in significant masses even today back in the late 80’s to mid-90’s. The rather vehement nay sayers were put to bed by satellite observations. (see second source)

…without any evidence of a comet or meteorite?

AND…it was "1,000x as powerful as Hiroshima"…and people and plant life there experienced damage to their DNA caused by >>radiation damage<< which resulted in birth defects and mutations. People living in the region got all kinds of cancers. Scientists and government officials didn’t even dare go to the region until 20 YEARS after the blast. Why? Did they know that the region had a lot of deadly radiation there?

http://en.wikipedia.org/wiki/Tunguska_event

Stuff blows up in the high atmosphere all the time. Tungaska was nothing compared to whatever caused the North American die off about 11-12 thousand years ago

Consider this recent report, on Yahoo News:

http://news.yahoo.com/s/space/20071115/sc_space/incrediblecometbiggerthanthesun

Okay….I actually do have a somewhat serious question about this. What would happen if we, on Earth, *hit* the comet somehow?(um, I think that’s how the grammar would parse, sorry) What if we hit the radically exploded coma, or dust cloud, of this thing? Assume that we don’t hit the core, since we know what that’s like (the Tunguska explosion over that Russian forest).

–Would it be a disaster?
–Would it be a total non-issue, like running over the Biggest Dust Bunny Ever (that is, something we don’t even notice)?
–Would it be something else entirely? (like a cool light show that lasts for *weeks on end*, or a source of atmospheric contamination)

And…I’m sorry, but "dust bunny" doesn’t cut it now. ^_^ Dust Eagle (like what you get from a ceiling fan occasionally)? Dust Mastodon? Dust Leviathan? What metaphor works now?

Thanks for your time.

Yes, it would pretty much be a total non-issue. The coma of the comet is so thin and diffuse we wouldn’t even notice anything if it *hit* us. (Not to mention that it’s about as far away as Jupiter’s orbit and moving away from us anyway.)

We would get an excellent view of the comet if we passed that close to it, though. It would most likely be bright enough to see in broad daylight.

Here is the Universe Today article:

http://www.universetoday.com/2009/03/27/was-the-tunguska-fireball-a-comet-chemical-bomb/

It’s a pretty cool proposal to explain the non-appearance of any piece of material from the object but I cannot seem to discount that an "earth-grazing" comet should have been visible before and after the event itself. New answer, more questions! Thanks in advance to those who would leave a reply!

Clear skies!..:-)
Overwhelming good replies!

Yahoo! seems overloaded, I cannot add any detail since yesterday.

I hope they can also cut one or two of the trees in the Lake Cheko area and see if indeed they are over a hundred years old or not as can be suggested by tree rings. There are suggestions that the trees around Lake Cheko are over a hundred years old so I guess if they are not felled down by the bolide, then Lake Cheko may not be the crater at all. Lake Cheko is 7-8km from ground zero but let’s all wait and see what they can haul out from the bottom of the lake. Shatter cones around the lake would also be good indicators. I’m also interested in phoenix’ statement regarding the spheroids.

That’s an interesting hypothesis, but I’m still leaning towards a rocky meteoroid airburst, rather than a cometary fragment. These types of airbursts are regularly observed in the upper atmosphere.

The reason I’m leaning this way is mainly on the physical evidence of silicate and magnetite spheroids found in both soil siftings and embedded in the trees. These show high proportions of nickel to iron, and are also rich in iridium. This evidence is consistent with a chondrite or carbonaceous chondrite meteorite, but those minerals are rarely associated with comets.

Further evidence may be forthcoming later this year, when a dense rocky body perhaps a meter across at the bottom of Lake Cheko will be investigated as a possible fragment of the impactor. Originally, the lake was not thought to be a result of this event due to sediment thickness, but more recent investigations contradict this assessment and date the lake at about 100 years. Its shape and orientation appear to be consistent with an impact feature (a conical lakebed with its long axis oriented toward the event hypocenter).

I’m not married to either hypothesis, but the available evidence seems to point to an impactor of asteroid origin.

EDIT: In response to your details regarding Lake Cheko… Yes, the lake is about 7 km from the hypocenter, and perhaps the trees were not felled. This is not inconsistent with the above, however. The energy of the explosion seems to have been concetrated along one axis. For example, the felled trees form a butterfly-shaped pattern: Those along that axis were felled for a greater distance than those orthogonal to it. Parts of the impactor along this axis would have likely been nearly completely vaporized, but pieces that were ejected near the equatorial plane of this axis may have survived to impact the ground.

Peer-reviewed journal references added.