Posted on July 11, 2004

Guest Column #1

Paradoxes of the Tunguska Meteorite Problem [1]

Academician N. V. Vasil’ev[2]

Tomsk division of the All-Union Astronomical-Geodesic Society
Proceedings of The HIGHER EDUCATIONAL INSTITUTES, No. 3 “Physics” 1992, pp.111-117.
(original Russian version posted at tunguska.ru.)

[Abstract:] This article adduces the basic data on the physics of the Tunguska explosion, and on the results of searches for the substance of the Tunguska meteorite. It substantiates notions as to the complex nature of this phenomenon, and as to its high degree of intricacy. It points out the difficulty of interpreting the Tunguska phenomenon within the framework of the existing scientific paradigm, including [that of] the currently most prevalent hypothesis — [namely,] that the Tunguska meteorite was cometary in nature. It points out a number of paradoxical circumstances related to the trajectory of the Tunguska cosmic body, to the geophysical consequences of the Tunguska catastrophe, and to the biological consequences it engendered in the region of the explosion. [In closing,] it points out the necessity of developing alternative interpretations of the Tunguska phenomenon.

Despite the many years of effort by investigators of the problem, the question of the Tunguska meteorite's nature remains unresolved to this day. Hypotheses proposed as explanations for this phenomenon may be divided into two groups:

1) those proceeding from the assumption that the Tunguska Meteorite (TM) belongs to one of the categories of small bodies of the solar system [1-3, 23, 31-35, 46, 47] — [i.e.,] to the asteroids or the comets;

2) those positing that it is of an unusual — even an artificial[3] — nature [2, 15, 16, 43-45].

Among the first group, those hypotheses positing the Tunguska Meteorite as a small asteroid [24, 25] have by now been, for all practical purposes, disavowed and offer essentially [only] historical interest. The cometary hypothesis has retained its significance and continues to undergo further development [18, 31-35]. Among the alternatives to it — the variants included in the second group of hypotheses — it makes sense to single out those versions regarding the Tunguska Meteorite as a plasmoid [13] and those positing an artificial, extraterrestrial nature for the TM [15, 16].

Considering that the majority of researchers into the nature of the Tunguska Meteorite adhere to the cometary hypothesis, it seems relevant to discuss a number of paradoxical circumstances of the Tunguska catastrophe — among them, some that are little known — which are difficult to fit into the framework of the given [cometary] conception. Ignoring these factors could push the further evolution of the problem onto a false path and hinder its final solution.

It would be incorrect to consider that the specific feature singling out the Tunguska phenomenon from a number of other impacts by gigantic meteorites is exclusively its scale. The TNT equivalent of the Tunguska explosion (10-40 megatons) and its energy (10e23-10e24 ergs) are, without question, very large; however, they are not the upper limit of the energy parameters associated with phenomena of this sort. Thus, the energy emitted during the formation of the Popigai astrobleme exceeded the energy of the Tunguska Meteorite by several orders of magnitude. The chief specific feature of the Tunguska phenomenon is its multifaceted nature, and this circumstance must be taken into account in formulating any concept which purports to explain the given phenomenon as a whole. It is necessary to bear in mind that the explosion of the cosmic body on the Stony Tunguska [river] on June 30, 1908 was the most striking and culminative, but far from the only episode in the complex chain of anomalous natural phenomena unfolding in the summer of 1908.

In discussing the paradoxical circumstances of the Tunguska catastrophe, it is necessary, above all, to dwell on certain peculiarities of its motion through the earth’s atmosphere.

It is known that the TM explosion was preceded by the flight of a gigantic daytime bolide over central Siberia, accompanied by exceptionally powerful sonic and luminous effects [10]. Analysis of the catalog of statements by the eyewitnesses to the catastrophe [11], whose overall number totals several hundred, reveals the circumstance, unexplained to this day, that thunderous sounds were observed not only during and after the bolide’s flight, but also prior to it. Such information is contained in a series of statements of eyewitnesses, who were situated at the time of the event in the populated points along the Angara [river], among them an extremely detailed description of the event by a political exile living in the village of Kezhma — [that is,] by a person of (to judge by everything) a rather high educational level. It is hardly realistic to explain away these [accounts] as subjective errors, since assertions of a similar sort are repeated more than once independently of one another. Since these observers were not infrequently located at distances measuring, at minimum, tens of kilometers from the zone of projection of the trajectory, it is evident that in the given case the reason for the sounds could not be the ballistic wave, since [that wave] was capable of lagging behind the bolide, but not of overtaking it. The only realistic explanation for this circumstance consists in admitting its connection with powerful electromagnetic phenomena; up till now, however, the question under consideration has not been studied from this angle.

The second, rather strange, circumstance is connected with the direction of the body’s motion. Analysis of the statements of witnesses, gathered in the immediate aftermath of the event [11] and in the 1920s and 30s [25, 28], led the first researchers of the problem (L. A. Kulik, I. S. Astapovich, and E. L. Krinov) to the unanimous conclusion that the bolide flew from south to north. However, the analysis of the vector structure of the forest-fall caused by the Tunguska meteorite’s shock wave yields an azimuth of 114 degrees [29, 30], and the zone of burn damage — [an azimuth of] 95 degrees, even [6-8]; that is, it testifies to the meteorite’s moving almost from east to west. It is necessary to add that this direction is also confirmed by analysis of the statements of those eyewitnesses living in the upper reaches of the Lower Tunguska [river] (the Preobrazhenki, Yerbogachen, and Nep regions) at the time of the Event.

The inconsistency here is obvious. Attempts to explain it were undertaken more than once, from various standpoints. In particular, the suggestion has made [13] that what took place over central Siberia on June 30, 1908 was the flight of not one, but several bolides. This interpretation, however, appears extremely farfetched, for the simple reason that, out of many hundreds of documented eyewitness statements, there is not one that mentions two bolides being observed in one day, although it is more than probable that the zones of observation overlapped in the case under consideration. F. Yu. Zigel’s version of the TM’s maneuvering in the earth’s atmosphere called forth a great deal of discussion. It, however, can be discussed in earnest only if we allow that the nature of the Tunguska cosmic body is artificial.

The culmination of the flight of the Tunguska meteorite was an explosive energy discharge, whose TNT equivalent ranged from 10 to 40 megatons, with a greater probablity of the upper level of the estimate [20-22, 27, 41]. Detailed characteristics of the destruction caused by the shock wave, as well as of the seismic, barographic, and other effects of the Tunguska explosion are to be found in a number of sources [1, 2, 27, 46, 47]. One of the most important brushstrokes in the “portrait” of the vector field of forest-fall formed by the shock wave is the presence of axisymmetrical deviations from a strict radial pattern, which occur in the zone of projection of the trajectory [29, 30] and constitute a trace of the ballistic wave. Further detailed analysis of the vector structure led, however, to the conclusion that the axisymmetrical deviations occur not only ahead of the epicenter, but also beyond it, along a continuation of the trajectory. Inasmuch as the only explanation proposed for these deviations from the radial pattern is the action of the ballistic wave, there follows the conclusion that the Tunguska meteorite (or, at least, part of it) did not end its existence at the moment of the explosion, but continued its motion along the trajectory at supersonic speed. If one considers that the nucleus of a comet of the sort that the Tunguska meteorite is proposed to have been consists of chunks of freezing gases with a density of one gram per cubic centimeter?, it is unclear how this sort of object, having these kinds of characteristics, could be preserved even partially after undergoing the super-powerful thermal and mechanical loads described above.

A key link in the study of the Tunguska meteorite’s nature is the question of its material (elemental and isotopic) composition. Beginning with the expeditions of L.A. Kulik, several generations of researchers were occupied with the search for the substance of the Tunguska meteorite. The results of these multi-year efforts are reflected in numerous review articles and original publications [23-25]. Nevertheless, today one may assert with complete confidence that a non-terrestrial substance which might be identified with certainty as the substance of the Tunguska meteorite has yet to be found.

It is impossible to explain this negative result as due to the insufficient sensitivity of the methodologies applied, for two reasons:

In the first place, the identical methods are being used successfully to carry out ecological profiling operations aimed at detecting traces of the precipitation of industrial aerosols, in quantities commensurate with those predicted in the given situation [6-8, 36-40].

In the second place, in the peats and soils of the Tunguska meteorite's impact area, the same methods detected a minimum of five types of finely dispersed, non-terrestrial substance,[4] representing traces of the background global precipitation of cosmic dust [6-8]. It is completely clear that, if the applied methodologies are sensitive enough to detect background precipitants, there can be no basis for thinking them inadequate to detect the tough[5], finely-dispersed substance of the Tunguska meteorite, in the event it is present.

This explanation of the Tunguska Event[6] is also rendered vulnerable to criticism by the absence in cometary nuclei of significant quantities of tough material: the probe of Halley’s comet under the rubric of the “Vega” and “Giotto” projects — while it did not offer the opportunity for a strict quantitative assessment of the proportion of the refractory component in the makeup of the cometary nucleus — nonetheless permits us to reckon that its contribution to the overall mass of the nucleus cannot be all that negligible.

In this connection, the opinion has been expressed that possibly the Tunguska meteorite had a makeup atypical of the small bodies of the solar system. Although there are no direct proofs of this, there are tangential circumstances corroborating it. They include the detection by the Italian researchers Galleo, Cecchini, et al. [42] of aerosol particles containing bismuth, tungsten combined with cobalt, and lead with bromine in the 1908 resin of trees that survived the Tunguska explosion near its epicenter. The aforesaid is not contradicted by a “peak” increase in the concentration of rare-earth elements, especially ytterbium, in the soil samples collected near the calculated center of the likely precipitation of the Tunguska meteorite’s substance [6-8]. Without attaching great importance to these findings, it would also be incorrect to underestimate them, inasmuch as the discussion concerns a clearly nontrivial event.

The biological consequences of the Tunguska explosion raise many questions, in particular the effect, discovered by the methods of mathematical population genetics, of an increase of the genotypic mutability of pine trees in the region of the catastrophe [14]. Statistically, this effect is highly trustworthy; it tends in the direction of the epicenter and of the trajectory projection, and cannot be reduced to the action of fire, forest-fall or other known changes in the ecological situation. The reason for it remains unexplained. The study of the radioactivity of soils and plants in the region of the catastrophe revealed variations in the limits of the natural background [radiation], although its values in the vicinity of the epicenter somewhat exceed those at the periphery of the region [ 9 ]. The study of changes in the thermoluminescent properties of the rocks [5] and soils [4], which are an indicator of the objects’ past radiation exposure, revealed a complex picture, not inconsistent with the notion that ionizing radiation may possibly be present in the spectrum of the physical factors of the Tunguska explosion. The absence of increased radioactivity compared to the natural background in the region of the epicenter cannot serve as a basis for denying it in the past, since, in the first place, the Tunguska explosion occurred at an altitude of 5-7 km, which minimizes its hypothetical local radiation consequences, and in the second place, from that time till the moment of the first (extremely crude) measurements more than 50 years had passed — a period more than sufficient for normalizing the overall radioactivity even at nuclear test sites.

Besides the local Anomalous Phenomenon of June 30, 1908, in central Siberia the summer of 1908 was marked by a complex of optical anomalies of the nocturnal and twilight sky, which began several days before the Event, reached a culmination on the night of June 30th to July 1st, exponentially decreased in intensity over the subsequent 2-3 days and finally died out toward the end of July. The basic components of this anomalous optical complex were bright (“volcanic”) twilights, propagations, extraordinary in their power, of fields of noctilucent clouds at an altitude of 80 km and, evidently, an intensification of the emissions of the night sky. A detailed description and catalog of these phenomena are given in [17, 26]; they are usually explained as the insertion of finely-dispersed material of cometary origin — more specifically, the comet’s tail — into the upper layers of earth’s atmosphere simultaneous with the fall of the meteorite. However, the latter was deflected by the pressure of solar rays to the side opposite the sun, which at 7 a.m. local time was located almost due east. Such is the explanation usually offered in describing the mechanism of the “bright nights” of 1908. More thorough analysis reveals, however, a number of serious difficulties, which can be reduced to the following fundamental aspects.

In the first place, the considerations given in [17] show that, in the situation in question, the tail of the hypothetical comet should have fallen, not on Western Europe or the European territory of Russia, much less on the Northern Caucasus, but, having “leapt over” the north pole, on Canada, which in actuality it did not.

In the second place, Academician V. G. Fesenkov [31-34], to whom we owe the most complete substantiation of the cometary hypothesis, showed that the particles of the cometary tail should, in view of their small size, have been arrested at an altitude of 200 km or higher and only gradually thereafter have “parachuted” down from there over a protracted stretch of time. At the same time, noctilucent clouds are found at an altitude of 80-82 km, whereas dawn-like phenomena form at an altitude of 50-60 km. The processes which provide for changes on the part of atmospheric polarization take place even lower, to say nothing of the numerous solar halos observed in those days. All this brought V.G. Fesenkov to the necessity of excluding from the set of atmospheric optical effects connected with the Tunguska meteorite practically all forms of anomaly, save one — its own emission into the night sky, whose presence, by the way, is the least proven, since direct measurements of [such] emissions were not yet a reality at that time.

In the third place, a comet’s basic structural components are the head, the tail, and the coma. The diameter of the dusty-gaseous coma for a comet whose size corresponds to the presumed Tunguska one is measured in the hundreds of kilometers, while its dustiness is considerably higher than the tail’s. It is logical, therefore, to expect that upon entering earth’s atmosphere the coma must fill [the atmosphere’s] upper part with dust for a distance of hundreds of kilometers not only to the west, but also to the east of the point of impact. In actuality, atmospheric optical anomalies were observed only to the west of the Yenisei and were not observed, to judge by everything, in Yakutia, which in no way agrees with the notion of a gas-dust shell’s presence in the Tunguska meteorite.

The aspects enumerated above do not exhaust all the difficulties which must be dealt with in an attempt to bring the cometary hypothesis into correspondence with the available factual materials. Serious difficulties also arise in attempting to interpret, from these standpoints, the geomagnetic effect caused by the Tunguska explosion [13], the estimates of the contribution of the Tunguska meteorite’s internal energy to the total yield of the explosion, the mechanism behind the origin of the forest fire which followed the explosion, and a number of other aspects.

Evidently, these circumstances explain the periodically undertaken attempts to interpret the phenomenology of the Tunguska catastrophe from nontraditional standpoints. In particular, there have been discussions in the literature of questions of the antimatter nature of the Tunguska meteorite [19, 45], of its belonging to a relic super-dense substance of the [early] universe[43], of the Tunguska meteorite as a transient energophore [13]. Not one of these alternatives was denied empirical testing; however, when all was said and done, only two of them were granted the right of further existence: the hypothesis of A. N. Dmitriev and V. K. Zhuravlev regarding the transient nature of the Tunguska meteorite, and that of F. Yu. Zigel’ and A. N. Zolotova regarding its artificial origin.

The first of these needs serious empirical reinforcement, inasmuch as even the very possibility that stable transients can exist remains thus far an open question. As far as the second is concerned, at present evidently, conditions are ripe to reconsider the a priori negative attitude toward any hypotheses based upon an assumption about the cosmic role of intelligent life. Being in complete agreement with V. I. Vernadskii’s doctrine of the noosphere, hypotheses of this sort cannot immediately be qualified as antiscientific, and have the right, at least, to be tested empirically. Since a final resolution of 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.

[1] In Russian, the Tunguska Object is commonly referred to as a “meteorite” — a convenient shorthand which does not, however, imply any prejudgment of the Object’s actual nature. As such, it is in use by both the cometary- and the asteroidal-origin adherents, as well as by those who belong to neither school (as here). [Return to text.]

[2] The late Nikolai Vladimirovich Vasil’ev (1930-2001) was a microbiologist by training. A world- famous immunologist who authored tens of books and hundreds of articles on the topic, he held, at various points throughout his career, the chair in immunology and allergiology at the Tomsk Medical Institute, and deputy directorships of oncology and microbiology at National Research Institutes in Tomsk and Kharkov respectively.
    He first became intrigued by the Tunguska Event in 1959, when he joined a group of Tunguska researchers led by Gennadii Plekhanov, and went on his first expedition to the impact zone. He would return there thirty-three times over the next forty-two years. He came to be the acknowledged dean of Soviet Tunguska studies, tirelessly publishing on his particular areas of research interest: the geomagnetic and radiation effects and optical anomalies accompanying the Event. [Return to text.]

[3] Here, and elsewhere throughout the text, the Russian word used is “technogenic” — i.e., referring to something created by, or a product of technology. There is no precisely equivalent adjective in English, but “artificial” comes close. [Return to text.]

[4] This is “cosmic substance” in the original Russian. [Return to text.]

[5] The actual word used is tugoplavkii, which my Russian-English dictionary unhelpfully renders as “refractory” (which, in turn, my English-English dictionary renders in this context as “difficult to fuse or to work, said of an ore or metal”). “Tough” seems to convey the intended meaning well enough. [Return to text.]

[6] In the original this reads “the explanation of the indicated result,” but it’s fairly clear from the context that the Event itself is the “result” Vasil’ev has in mind. [Return to text.]

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