This isn't something I'm an expert on, but I did talk to an astronomer about this recently (he is a serious professional astronomer, I am only sub-amateur hobbyist). Meteors and impact craters are not in his area of specialty, which is bad (because it means he doesn't know as much about it as he might otherwise) and also good (because he is not necessarily under tenure-track, publish-or-perish obligation to any particular viewpoint). He just seemed like a really down-to-earth guy, and he seemed genuinely convinced (and fairly persuasive) that the thing that blew up over Tunguska is thought to be a (carbonaceous?) chondrite meteor. I didn't talk with him about crater evidence, but he had just spent two hours talking with our local amateur astronomy club about meteorites and craters. The question of a crater is such an obvious thing that I can't imagine this person would not have thought of it. On the other hand, I didn't know we'd be slashdotting over it, so I didn't ask!
I have heard that the rather complex tree-flattening patterns (I'm sure they have a better term for that) can be explained by either comet or meteor. One difference between comet and meteor is that since a comet is just a big snowball, it would not be expected to reach the surface. Basically the ice would sublimate / evaporate / plasmasize / whatever and then vaporize, leaving no residual evidence. But the meteorite theory allows for something with more appropriate mass, and this particular type of meteorite would be difficult to detect. Even when people see them fall (which is very rare, I'm sure) this professor was explaining how they have to be collected right away. If you don't, this type of meteorite will deteriorate to the point where you can't really tell that "some of that dirt over there came from space" without doing some chemical analysis.
So my understanding of the theory is: it's sort of like a big shotgun firing a huge dirt clod at us. Weird, huh? It was the astronomy professor who actually said these things are like dirt clods, btw. Would it leave a crater? Maybe - depends on dispersal, the height of the meteor when it "exploded," and lots of other factors, I suppose. But I've been told that the residue it would leave would be hard for non-geologists to distinguish from, well, dirt.
As a sidebar: Impact craters aren't always easy things to identify, you know. There's one here in Iowa that was once a candidate for the "meteor that killed the dinosaurs" award. The weird thing is that you can't see it, unless you look at subterranean geologic data. Of course the Tunguska even is much more current - I'm not saying that a Tunguska crater would have filled up in about 100 years. But the point is that craters don't always look like the ones on the moon. And if the Tunguska event was an overhead explosion (as many believe), then the impact crater would be much less pronounced.
Anyway, I was commenting based largely on what this astronomy professor had shared with me recently. Feel free to disagree - I just thought it was interesting. Personally, I don't think anybody's saying we *know* what happened at Tunguska.
Actually, if the "asteroid" was made of water, wouldn't you call that... a "comet?"
But as long as we're talking official theories, I believe the current theory is that the meteor was a chondrite (a carbonaceous chondrite, I think), which is a type of meteor that has about the same consistency as a dirt clod. If you slam a big dirt clod into a field of dirt, what happens? Well, apparently you can blow away lots of trees and get a lot of conspiracy theories going, but you can't find the dirt clod itself because it's all mixed into the earth itself. Chemical testing of the soils in the Tunguska region support this theory, by the way.
Slashdot Mirror
> wouldnt there be a creater (crater)?
Not necessarily.
This isn't something I'm an expert on, but I did talk to an astronomer about this recently (he is a serious professional astronomer, I am only sub-amateur hobbyist). Meteors and impact craters are not in his area of specialty, which is bad (because it means he doesn't know as much about it as he might otherwise) and also good (because he is not necessarily under tenure-track, publish-or-perish obligation to any particular viewpoint). He just seemed like a really down-to-earth guy, and he seemed genuinely convinced (and fairly persuasive) that the thing that blew up over Tunguska is thought to be a (carbonaceous?) chondrite meteor. I didn't talk with him about crater evidence, but he had just spent two hours talking with our local amateur astronomy club about meteorites and craters. The question of a crater is such an obvious thing that I can't imagine this person would not have thought of it. On the other hand, I didn't know we'd be slashdotting over it, so I didn't ask!
I have heard that the rather complex tree-flattening patterns (I'm sure they have a better term for that) can be explained by either comet or meteor. One difference between comet and meteor is that since a comet is just a big snowball, it would not be expected to reach the surface. Basically the ice would sublimate / evaporate / plasmasize / whatever and then vaporize, leaving no residual evidence. But the meteorite theory allows for something with more appropriate mass, and this particular type of meteorite would be difficult to detect. Even when people see them fall (which is very rare, I'm sure) this professor was explaining how they have to be collected right away. If you don't, this type of meteorite will deteriorate to the point where you can't really tell that "some of that dirt over there came from space" without doing some chemical analysis.
So my understanding of the theory is: it's sort of like a big shotgun firing a huge dirt clod at us. Weird, huh? It was the astronomy professor who actually said these things are like dirt clods, btw. Would it leave a crater? Maybe - depends on dispersal, the height of the meteor when it "exploded," and lots of other factors, I suppose. But I've been told that the residue it would leave would be hard for non-geologists to distinguish from, well, dirt.
As a sidebar: Impact craters aren't always easy things to identify, you know. There's one here in Iowa that was once a candidate for the "meteor that killed the dinosaurs" award. The weird thing is that you can't see it, unless you look at subterranean geologic data. Of course the Tunguska even is much more current - I'm not saying that a Tunguska crater would have filled up in about 100 years. But the point is that craters don't always look like the ones on the moon. And if the Tunguska event was an overhead explosion (as many believe), then the impact crater would be much less pronounced.
Anyway, I was commenting based largely on what this astronomy professor had shared with me recently. Feel free to disagree - I just thought it was interesting. Personally, I don't think anybody's saying we *know* what happened at Tunguska.
Just my 0.02.
Actually, if the "asteroid" was made of water, wouldn't you call that ... a "comet?"
But as long as we're talking official theories, I believe the current theory is that the meteor was a chondrite (a carbonaceous chondrite, I think), which is a type of meteor that has about the same consistency as a dirt clod. If you slam a big dirt clod into a field of dirt, what happens? Well, apparently you can blow away lots of trees and get a lot of conspiracy theories going, but you can't find the dirt clod itself because it's all mixed into the earth itself. Chemical testing of the soils in the Tunguska region support this theory, by the way.