From what I understand, you've got to make quite a few far-fetched assumptions to attribute the tunguska blast to anything we've seen in our solar system (asteroids don't tend to explode in mid air).

Now I'm not saying anything for certain, but lets just say it *might* have been an alien spacecraft.

If it were, this would provide an explaination of the fermi paradox. Aliens DID try and contact us, but some clumsy ET plowed their flying saucer into Siberia and was never heard of again. The aliens who came to say 'hello' may have believed us to be a hostile species, and decided to give us a wide bearth for a bit.

This isn't good if they are friendly (which would be likely given my scenario) - we want to meet them. Thus we should start transmitting some kind of pictorial depiction of the tunguska blast out into the cosmos, to let the owners of the flying saucer involved know what happened and that we were not responsible.

Of course, if it wasn't a flying saucer, we've just transmitted a load of messages into space that won't mean a great deal to anyone. No loss really.

Sufficiently large rocks falling from space through the atmosphere do tend to explode in midair, as far as I know.

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I'm not convinced of this, can you point me to an example?

Actually they do...if they happen to be stony, and enter the atmosphere at 20Kps.

This is a nice short article:
http://www.imperial.ac.uk/P4317.htm

another article

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Sure

edited to add...not actually an "example", just an explanation of the Tunguska event.

If the mechanical stresses of re-entry cause it to break up in a 15 megaton explosion, why did it seem to remain pretty much intact well into the atmosphere?

Because the atmosphere thins out very rapidly. Only the lowest kms are think enough. Add to this the large velocity of the asteroids, and you've got the reason they can come close to the surface before exloding. The lower thick atmoshpere is seen as a wall to the approaching asteroid.

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Now this is a little bit on the disconcerting side (from R.A.F.'s link):

Too close for comfort!

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There have been no other incidents that can be compared to tunguska which we have records of (and due to political turmoil in the area at the time, we don't have a great deal of good information on tunguska). This means any hypothesis is going to be largely guesswork anyway.

I'm not saying it definitely, 100% certainly was an alien spacecraft - I'm just saying that the possibility of it being so is significant enough to warrant the very slight effort of trying to inform said aliens of the fate of their spacecraft.

Any trace of debris or exotic substances at Tunguska?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

The chance of occurence is one in 100 years. On more than 3/4 of earth, nobody would notice the explosion itself (the nightglow is omething else). Even Tunguska went by almost unseen. Therefore I think it is normal that we have no other recorded events to compare with.

I think an asteroid is far more likely than a spaceship (for the simple reason that we've seen more asteroids than spaceships amongst others).

I think that the possibility of a crashed spaceship, coming from a species that assume an attack when they lose a craft without further information, who don't seek any further information about the event , is a rather thin reason to send info about the event.

How would you send a clear and understandable message that the possible craft that possibly crashed at Tunguska (who says it wasn't attackng us?) wasn't shot down by us and that we are peaceful? It will be more than difficult to send out a message that is clearly artificial to any species, let alone be heard by an alien species.

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The traces of whatever exploded are all microscopic. When ground up into nanometre sized particles, spaceships and asteroids are tricky to tell apart.

How can you possibly state that it should occur once every 100 years when there is only one example of it ever occuring? I would expect at least 30 such documented events to draw such a conclusion.

True, but the number of asteroids we have seen create 15 megaton explosions is at best 1.

I admit the possibility is remote - but given that its hardly an effort to send out the signal its worth it. As for why they wouldn't come again - in the decades following the tunguska event humans spent a great deal of time and energy killing other humans, and transmitting accounts of this slaughter into space.

If they visited, they know we are here, so they would be looking in our direction and probably have figured out what our transmissions look like.

I took over that 100 years frequency from the link I provided earlier. Those numbers can be found from statistics of number of asteroids, how many have an earth bound orbit, size of asteroids, inter/extrapolation of impacts of objects of other sizes, etc.

About us sending messages into space, the amount of energy of those messages aimed into space is not large, so I don't know how far they would reah. Does anyone have information about this?

do you mean the transmissions like those war accounts you referred to earlier, or the Tunguska message you suggest? Becasue if you mean the war accounts, they would have heard our other "private" messages as well, which also account peaceful events, and information about Tunguska.

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Do you assume that the explosion pulverized completely the spaceship? Not even a screw or a nut survived? A black box?
A nuclear explosion does not pulverize or vapourize everything.
And if the spaceship was made of material different from the usual meteorites? Samples from the soil of the region might show it.
Or do you think that all the material was transmutated into something less exotic?

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

I'm dying to know how you get frequency data for a one off event. Our serious observations of the solar system have taken place over a cosmicly trivial period of time, and we still suffer errors (i.e. all those near earth asteroid false alarms).

Funny thing about em radiation, its got infinite range. If they have visited, its fairly safe to assume they can take care of the receiving end.

Maybe, maybe not. If aliens have visited us its impossible to tell what they know about us, and how they have intepretted that information. Its also irrelevant to the discussion at hand.

You have clearly decided that the most popular explanation of the event HAS to be the truth and any other has to be a woo-woo conspiracy theory. The fact is that my theory is definitely possible, and it (at least partially) accounts for the lack of alien presence in our solar system.

Given the very small amount of effort and resources required to act on this theory, there is little reason not to.

Bear in mind that for the asteroid theory, not a single part of the asteroid was completely pulverised. Rocks floating around space have some geological features that can tell you something about them (I'm guessing here, I'm not a geologist) - so I could turn your objection round and ask how can you think it was an asteroid when such features that can be used to identify one have been conviniently pulverised?

A 15 megaton explosion DOES pulverise or vapourise anything, at the range we are talking about. This is demonstratably true in the tunguska case regardless of whether it was a rock or a flying saucer that exploded: nothing macroscopic seems to have survived.

Pulverised does not mean that the elements have been transmuted.
If it was an iron-nickel meteorite pulverised in the explosion, I would expect to find iron-nickel dust on the ground, in larger amounts than in neighbouring regions.
That's why I mentioned samples of the soil.

So, if there is nothing that looks artificial and there is no trace of exotic materials, and we know that meteorites can make such explosions, why would you think that it might have been a spaceship.

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

Seems to me to be a case of what's simply more probable. Sure, it's not *impossible* that this explosion could have been an alien space craft but it's far more *probable* that it was a stony asteroid. We know that these type of asteroids exist and upon occassion come our way...we simply don't know anything about aliens.

As for Earth's lack of alien visitation; they may simply be too far away, they may have checked us out in the distant past (and we weren't aware of it) or perhaps we are the pinnacle of technological civilization in the galaxy. It just can't be said that the destruction of an alien space ship is the most probable reason for our lack of "neighbors" paying us a visit.

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The elements on the ground were elements you'ld find in an asteroid.

Just out of interest, if you wanted to build an interstellar spaceship, where would you get the raw materials from?

Its not a matter of thinking it is a spaceship, its a matter of thinking it could be, and that it being one might shed some light on the fermi paradox.

Yeah...what N C said.

But not necessarily in the ground where it exploded.

I am not engineer, let alone alien, so I would not know which raw materials would be more suitable.

I agree with N C More on this point.
But I find unlikely that not a single artefact would survive the explosion.

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papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

Emphasis mine. Unless they made their spaceship out of pur rock or iron, they're going to have used some sort of alloy. An explosion isn't going to dealloy the alloys back into their base (raw) material. So some sort of trace amounts of the alloys used should have been detected.

I'm willing to accept that the stony asteroid theory has more probability (although because we don't know about aliens its impossible to calculate) - but that still doesn't mean we shouldn't explore all possibilities, especially when it costs us little to do so.

Overall, no. But ask yourself this: if aliens had visited prior to 1908 how would we have spotted them? It is only in very recent history that we really have to account for the non-presence of aliens.

As for us being the pinnacle of technological civilization - that is a far more improbable theory than mine.

Are you're saying that the wreckage of an alien spaceship would be indistinguishable from that of an exploded asteroid? I don't buy it.

Humans had eyes before 1908, and bored shepherds have been watching the sky for thousands of years.
And let's not forget astronomers.

Why?

__________________
papageno


"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

And you think the material in asteroids is arranged in nice little elemetal blocks?

A 15 megaton explosion is BIG. I am quite confident it will destory any evidence of an alloy being made by virtue of the fact it would vapourise the entire spacecraft.

Account for their non-presence?

What do you mean by that?