Star Wars —
By Dr. John C. (“Jack”) Adler, as told to Bill DeSmedt
When we left off last time, Tunguska research had just taken a giant step forward with help from a science-fiction story — Aleksandr Kazantsev’s 1946 “Explosion” (“Vzryv!”).
Once it was corroborated in the mid-sixties by Igor Zotkin’s scale-model simulations, Kazantsev’s notion that the Tunguska Object might have exploded in mid-air had pretty much solved the no-crater problem. Meteors and comets were both back on the table.
It was the first real breakthrough in Tunguska studies — the one everybody’d been hoping for.
Unfortunately, it was also the last.
You’d think all that was left to do was pick up the pieces: Find enough in the way of evidence to decide between comet and meteor, declare the mystery solved, and go home.
Didn’t work out that way.
Then as now, the most painstaking fieldwork on site, the most meticulous analysis back in the lab, never succeeded in turning up more than a few trace elements in the soils, peats, and tree resins of Tunguska. And there was, and is, no way to know for certain those traces weren’t just by-products of the flash fire that incinerated thousands of square miles of taiga the morning of the Event, or the results of an especially heavy concentration of the normal background infall of meteoric dust and debris that rains down all over the earth, day in and day out.
It’s for sure nobody’s ever found a chunk of stuff big enough to see with the naked eye, much less heft in your hand — and that’s from an object that, going by the blast wave energy, supposedly weighed anywhere from fifty to five hundred thousand tons!
No, no matter how long you mull it over, there just isn’t enough evidence on the ground to tell for sure if the object that exploded high over the taiga back in 1908 was a meteorite or a comet — or something else entirely.
So, what do you do in a situation like that, when there’s just no telling one way or the other? How can folks like Tom Gehrels be so sure it “was a comet or asteroid,” like we saw last time [Gehrels 1996]?
For all the hard evidence there is, it could just as well have been Aleksandr Kazantsev’s little green men from Mars.
Well, wouldn’t you know, science has got a rule for what to do in case of a toss-up. It’s called Ockham’s Razor, after William of Ockham, the 14th century English philosopher who thought it up. And what the Razor says is: “do not multiply causes beyond necessity.” Or, to put that in plain, ordinary Texan: if all else fails, pick the simplest explanation that fits the facts — where “simplest” can mean, among other things, “most commonplace.”
And let’s face it, folks, comets and asteroids are a lot more commonplace than tiny black holes (which have never been observed in nature), not to mention way stranger stuff that’s been posited — like antimatter or “mirror matter” or even UFOs.
In other words, in the absence of any evidence whatsoever, you’re best off going with a comet or an asteroid.
So, are we done yet? Can we all go home now?
Not quite. Because it’s like Albert Einstein says: “Everything should be made as simple as possible, but not simpler.” No matter how simple an explanation is, it’s not going to be worth the paper it’s written on if it doesn’t fit the facts. And it so happens that, while there isn’t any hard evidence for either of the two leading contenders, there is a certain amount of evidence against them.
And that right there changes the groundrules. If you’ve got any evidence pro or con, Ockham’s Razor goes right out the window, along with the strop. And different rules of engagement kick in instead — namely, like Carl Sagan used to say [Sagan 1980]:
The critical issue is the quality of the purported evidence, rigorously and skeptically scrutinized — not what sounds plausible …
Now, Carl was talking about really “extraordinary claims” (namely, UFOs) when he said that. And it’s for sure that nowadays meteorites and comets happen to be far less extraordinary — hence, more plausible — than flying saucers. But that doesn’t mean we should let those less extraordinary theories off the hook altogether either.
After all, it wasn’t but a couple hundred years ago that then-president Thomas Jefferson, on hearing reports from Yale University of a meteorite crashing in Weston, Connecticut, remarked [Ofgang 2020] —
It is easier to believe that two Yankee professors could lie than to admit that stones could fall from heaven.
Back then, in other words, Ockham’s Razor would have cut against the meteorite explanation, too.
What all this means is that, somewhere along the way even the most mundane explanations have got to stand up to Carl Sagan’s same rigorous and skeptical scrutiny. Sure, maybe you give them more of the benefit of the doubt, but only as long as they aren’t flying in the face of the facts.
So, just what are the facts? The facts that’ve kept the comet-vs.-meteorite controversy simmering all down through the decades?
Well, lacking any knock-down physical evidence one way or the other (no crater, remember?), the two camps have been throwing everything else into the pot, from Zdenek Sekanina’s distillation of everything written on Tunguska up to 1983 [Sekanina 1983], to Mark Boslough’s computer simulations of blast patterns [Boslough 1984], to Luigi Foschini’s announcement of a “solution” based on orbit probabilities [Foschini 2001] … the list goes on.
And, while nobody’s managed to come up with a proof of their own position, be it pro-meteorite or pro-comet, they have managed to put some dents in the other side’s theory along the way.
Here’s a sampling:
- The absence of physical evidence on the ground has itself been taken as evidence against the stony-meteorite hypothesis by V. Bronshten [Bronshten 2000].
According to him —
[T]he complete lack of stony fragments over the area affected by the shock waves generated either by the meteorite itself or by its explosion is in itself sufficient to reject the hypothesis that the Tunguska body is an asteroid…
[N]either the radiation from the fireball nor the interaction with the air flow after the explosion can evaporate stony fragments of the hypothetical body of asteroidal nature. Therefore, this body could not be stony. Only the icy nucleus of a comet could explode without leaving large fragments.”
- But Zdenek Sekanina turns that argument on its head [Sekanina 1998]: The “icy nucleus” of a comet, he says, is way too fragile to have survived a plunge into the lower atmosphere — the heat of atmospheric friction should have vaporized it at an altitude of 200 kilometers, much too high to cause the observed blast effects on the ground.
- Those blast effects raise another problem for Academician Nikolai V. Vasil’ev [Vasil’ev 1992] of Tomsk University. According to him, careful analysis of the treefall pattern hints that some part of the object continued on course after the first, multi-megaton air-burst. That’s really hard to square with the fragile nature of a cometary nucleus. After all, being basically just “dirty snowballs,” they’re not much denser than water. And a meteorite doesn’t come off looking much better — because if a piece of rock or iron made it through the main explosion intact, then where is it?
(At the bottom of Lake Cheko, I can hear some of you saying. We’ll take that one on soon, but it’s going to need a whole seminar to itself.)
- Then, there’s the geomagnetic storm that raged for four hours after the Event [Zhuravlev 1996]. It’s hard to see how a comet could have stirred that up.
- As for the magnetic anomalies L. Weber recorded at Kiel University on the three nights leading up to the impact [Weber 1908], it’s even harder to see how a comet or an asteroid could have generated those — from a couple million miles out in space.
I could go on, but you get the idea. Maybe any one or two of these objections could be shrugged off. But taken all together, they were enough to make that grand old man of Tunguska studies, Academician Nikolai Vasil’ev, throw up his hands in despair. His summational article on “Paradoxes of the Tunguska Meteorite Problem” [Vasil’ev 1992] winds up like this:
Since a final resolution to the question of the Tunguska phenomenon’s nature has yet to be found, and since it must be acknowledged that the perennial attempts to interpret it within the framework of the classical paradigm have so far brought no decisive success, it seems expedient to examine and test alternative ways of explaining it.
“Examine and test alternative ways of explaining it.” In other words, if your pet theories aren’t either of them panning out, why not try something different? Sounds like pretty good advice, doesn’t it?
It fell on deaf ears, though … as we’ll see next time.
[Gehrels 1996] Tom Gehrels, “Collisions with Comets and Asteroids,” Scientific American, March 1996, pp. 54-59.
[Ofgang 2020] Erik Ofgang, “In December 1807, a Meteorite Fell from the Sky above CT and into Scientific History,” Connecticut Magazine, November 17, 2020.
[Sagan 1980] Carl Sagan, Cosmos, Random House, 1980.
[Sekanina 1983] Zdenek Sekanina, “The Tunguska event: no cometary signature in evidence,” Astronomical Journal, 1983, vol. 88, No. 1, pp. 1382-1414.
[Foschini 2001] Luigi Foschini, “A Solution for the Tunguska Event,” astro-ph/9808312v2, 16 December 2001 at: http://www.arxiv.org.
[Bronshten 2000] V. Bronshten, “On the nature of the Tunguska meteorite,” Astronomy and Astrophysics, 2000, No. 359, pp. 777–779.
[Sekanina 1998] Zdenek Sekanina, “Evidence for Asteroidal Origin of the Tunguska Object,” Planetary and Space Science, 1998, vol. 46, No. 2/3, pp. 191-204.
[Vasil’ev 1992] Nikolai V. Vasil’ev, “Paradoxes of the Tunguska Meteorite Problem,” Proceedings of the Higher Educational Institutes, No. 3 “Physics,“ 1992, pp. 111-117, http://www.tunguska.ru/obzor/stat/.
[Zhuravlev 1996] Victor Zhuravlev, “Geomagnetic Effects as one Aspect of the Tunguska Event,” Paper delivered at the International Workshop Tunguska – 1996 Bologna, Italy, at: http://omzg.sscc.ru/tunguska/en/articlese/zhur_us.html
[Weber 1908] L. Weber, “On the lightshow in the night sky at the beginning of July,” Astronomische Nachrichten, 1908, Vol. 178, No. 4262, pp. 239-240.