It’s because years ago I learned that the majority of asteroids are metallic/rocky lumps; thinking back, that may have been from the perspective of our asteroid belt, as they were leftovers from the forming of the Solar System. I yield to your better explanation, though.
Tripler
The point, as per the OP, is a metric ass-ton of boom over Siberia.
Asteroids are pretty diverse. The ones that are solid metal or a combination of solid metal and silicates are the remnants of asteroids that grew big enough to melt and differentiate into a core, mantle and crust, then suffer a giant collision and be completely shattered. Then there are stony asteroids that never got big enough to melt and differentiate but are still very solid. But there are also large numbers of asteroids that are just barely stuck together and not much different from comets other than they consolidated too close to the Sun to keep their volatiles. A comet is a dirty snowball or a snowy dirtball, a primate asteroid is the same thing without most of the ices. (I mentioned Tagish Lake before–it is pretty much a toss-up as to consider it an asteroid fragment or a comet fragment.) An example of a primitive dirtball landed just last year.
The fact that there haven’t been recovered fragments of Tunguska when there should have been, both immediately afterwards and later, suggests to me that the whole thing was pulverized to dust miles above ground.
Sikhote-Alin was mentioned earlier–that iron was much smaller than the Tunguska bolide, but it left behind 24 major craters and 98 smaller ones (however they define the terms–the largest was 26 meters across.)
http://www.arizonaskiesmeteorites.com/AZ_Skies_Links/SikhoteBackground/index.html
(Here is a map of the strewn field, but in Russian.)
And there is the Campo de Cielo iron–it fell several thousand years ago yet at least 26 craters are still discernable today, the largest 115 meters across. (Also tiny compared to Tunguska.)
A strewn field from Tunguska would have been really, really unsubtile.
(Huh. Anybody got any ideas why the first stand-alone link didn’t get a “onebox” like the second one?)
This, I did not know. . . thank you!
[Hijack] I just got a silly One Box badge for something I posted way back in Jul 2001. Did you get a badge from a way-earlier post? [/Hijack]
Tripler
Aahhhh, the birds and the bees of interplanetary rock formations.
Before opening this thread, from the thread’s title I was guessing this was about Tunguska.
About the diverse types of asteroids, at Meteor Crater near Flagstaff, AZ they have a piece of the meteorite on display and you can touch it. I was surprised that when I gently knocked on it with my closed Swiss Army Knife, it rang back with a metallic ring.
Check out pallasites, which probably formed at the core/mantle boundary in differintiated asteroids. Olivine crystals mixed into nickle/iron.
Another good example of what is left behind by Big Iron. Around 30 tons of shrapnel from that one have been recovered (after close to 50,000 years). An estimated several thousand more tons are in the miles surrounding the crater in the form of Nininger Spherules.
[quote=“Darren_Garrison, post:48, topic:913873”]
Another good example of what is left behind by Big Iron. Around 30 tons of shrapnel from that one have been recovered (after close to 50,000 years). An estimated several thousand more tons are in the miles surrounding the crater in the form of Nininger Spherules .[/quote]
Incredible. I’ve been once to Meteor Crater, with my mom. My wife hasn’t been. I’d like to return and bring her. The crater and the visitor center are great to visit, I’d like to go again.
The crater has an interesting recent human history, too, as I posted here. (Here is a journalist saying the same thing with lots more words.)
The Barringer family used to let some people continue to search for meteorites from around the crater with metal detectors, but people didn’t fill their holes back in, putting the family’s cattle at risk, so they stopped. Probably tons of shrapnel still around the crater.
I researched the Tunguska event, reading Leonid Kulik’s reports in translation and writing an (unpublished, as yet) article about it. Fascinating topic. It’s like a cosmic Rorschach test – people saw their pet theories reflected in it, whether they thought it was a ball of cosmic dust, a ricocheting meteor, a piece of antimatter (proposed three separate tiumes) or a quantum black hole (or an exploding alien spacecraft, to get really absurd). The comet/loosely bound solid theory is clearly the best.
I have to pojint out that the 1960 expedition DID find solid remains, in the form of microscopic dust, scattered in an elliptical region near the site. The bits werer both stony and nickel-iron, and had melted into spherical globules.
In addition, although no one seems to remember it, Kulik claimed to have found a fist-sized piece of metal meteor near the site. So a macroscopic chuck possibly made it to earth.
As the burst pattern shows – “telegraph pole” trees denuded of branches near the center, trees felled flat outwards from the center away from the center – there was an air burst several kilometers up. The heat appears to have melted the permafrost, because there were several “craters” with a twenty-year growth of sphagn7um moss near the center (Kulik’s first expedition got there in 1927, nearly twenty years after the event). Kulik had an aerial photomosaic of the downed trees made, covering a huge area on the order of ten miles out from the center. I’ve only seen a very poor, low-resolution photo of this. I wonder if a good copy exists anywhere.
The Metbase entry lists nine globules, ranging from 0.03 to 0.06 mm, from the 1957 expedition. From the 1960/1961 expeditions, it was said
All of the previous samples that were collected in the vicinity of the epicenter (as well as the 1961 samples) exhibited an altogether negligible concentration of spheres. Since the average number of such particles had not been established for the soils, they can easily be attributed to the back ground concentration of meteoritic dust of this type.
Here is an article from 2013 that shows that as of 7 years ago none of the recovered material is undisputedly connected to Tunguska.
https://www.nature.com/news/rock-samples-suggest-meteor-caused-tunguska-blast-1.13163
If you look at the original paper, it shows a large concentration of dust in an elliptical pattern around the Tunguska site. It passes belief that this concentration near the explosion is due to unassociated “background” micrometeorites. And it consisted almost entirely of spherical particles.
Kulik’s claimed large piece was found during the 1920s expeditions.
Steve Wilk/”CalMeacham”
Strewn fields for meteorite falls do form an oval of varying degrees of enongation. It takes this shape because different sized/shaped pieces have different air resistance, with smallest pieces mostly at the beginning of the field and the biggest pieces at the end. There is nothing about microspherules that would require them to be distributed in an oval–especially since (as per the metbase entry) the spherules are thought to have been part of the smoke trail of the object, which would mean distribution in a ragged wind-blown line up to hundreds of miles long.
And the found then lost stone of Kulik’s, it is described as “glassy with bubbles”, which isn’t an especially likely description of a meteorite. (Some achondrites such as The Rock From La Mancha can have a glassy fusion crust–bubbles not so much.)
Darren Garrison/“Darren_Garrison”
I am honestly confused by your response, which seems not entirely related to what I wrote in reply to you.
1.) I observed that in the articles that were published with results from the 1960s expeditions they reported microscopic meteor spheroids that were found in an approximjately elliptical region around the center of the airburst. (There was a map in one article showing the distribution of spheroids, and there were pictures of the spheroids as well). It seems odd to assert that no such pieces were found, especially when there were pictures. Are you saying that they were somehow mistaken? or were fabricating results?
2.) My claim that the spheroids were found in a distribution around the center was in reply to your statement that any micrometeorites were simply “background”. My point was that it was odd, then, that the “background” only coincided with the burst region. The point being, of course, that it didn’t seem likely that the “microometeorites” and the Tunguska blast were unrelated.
3.) Why you should take issue with the microspheres being in an elliptical distribution while the dynamics are clearly different from the case of macroscopic meteorite falls is pretty much irrelevant – I never claimed that they had that distribution because they were created by a standard meteorite fall. There certain IS a reason for the particles to be concentrated in a roughly circular area around the burst center if they were created by that burst (and the fact that the particles were in spherical form, especially of joined stony and nickel-iron pieces, suggests that they were formed in the great heat of the explosion). Certainly some would be carried further away, but you’d expect a large concentration underneath the blast.
4.) As for the trail of the bolide, it certainly was extremely long – it injected dust into the atmosphere over Europe, cas=using extreme scattering phenomena that caused the night to be brilliantly lit up. Torvald Kul of Norway even wrote at the time that he saw this as evidence of a meteorite fall somewhewre. But that dust trail was likely of much smaller particles, and not directly related to the explosion at the Tunguska site.
5.) You evidently have more information about the large piece Kulik found than I had, because I lack ac description. I admit that his find might not, in fact, be a fragment from the meteorite, but I see no reason to disbelieve it, either.
Okay, I will break it down for you. You clearly find the evidence of these microspherules having been from the Tunguska blast compelling. But scientists who actually specalize in the area and have built their careers on it lack your confidence–hence you see scientific paper after scientific paper saying that there are no confirmed samples of the Tunguska object.
There were spheroids found. But they were very sparse, and there is a global background of spheroids from meteor vapor trails.
In addition, there has been for a couple of decades now conflict in the relevant scientific communities about the possibility of significant late ice age impacts. There is much skepticism, but there sure seem to be plenty of microspherules in the arctic.
So there is no question that a tiny fraction of microspherules were found. What is in question is the origin. And the methodology–how many samples did he take to determine both the shape and size of the oval area? How sure is the data that the area is oval and not round or a long line? How was he sure that nothing was ouside that area? How sure is it that the microspherules were from the correct, unreworked stratigraphic layer? Did he draw the area to be an oval over sparse data points because he was conditioned to expect an oval based on what was known about the strewn fields of macroscopic meteorites? I haven’t seen the original work, but it evidently isn’t compelling to professional scientists in the area. It may in fact be from the 1908 object, but it doesn’t reach the standard of evidence to be fully accepted.
Moreover you were the one crowing about it is elliptical expecting that to seem significant, and it is entirely relevant that the reason meteorite strewnfields are elliptical is irrelevant to vapor trail particles.
I suggest you do a little more research before writing your article.
(FWIW, here is the latest computer modeling):
I think I am more inclined to believe the database of the International Society for Meteoritics and Planetary Science. And as I have pointed out in this thread, the database lists the recorded particles from the 1957 expedition to be from the smoke trail. The segment quoting that is from this meteorlogical bulletin (PDF). You will also note that “the editor (of the professional database) is unaware of confirmed recovery of meteorites.”
('“Smoke trail” is a somewhat deceptive term–it includes all droplets ablated off the bolide, not just traditional “smoke particle” sized ones. Droplets run off meteors in streams like water.)
Isn’t St Petersburg at the same latitude as Tunguska? World history would be very different indeed if the event occurred a few hours later.
A new really good article on a lump of clay that fell last year.