On March 13, 2003, ?Izvestia? reported on the results produced by a scientific expedition looking for traces of the Vitim meteorite that fell in the vicinity of Mama village, in the northeastern part of Irkutsk region. American military satellites spotted the falling of the meteorite last September. Lately the news agencies have reported that the expedition organized by ?Kosmopoisk? had located the position of the fallout and found some fragments of the Vitim bolide. Sergei Yazev, Director of Astronomical Observatory of the Irkutsk State University, a researcher at the Institute of Solar-Terrestrial Physics of the Russian Academy of Sciences, has commented on the news at our request.
US Air Force satellite recorded the passing of the Vitim in the small hours of September 25, 2002. Coordinates of the bolide?s position point and those of the loss-of- signal point were made public two weeks later. The altitude above the earth?s surface of the former point was 62 kilometers, the altitude of the later one was 30 kilometers. Those coordinates enabled scientists to define a trajectory inclination angle (approximately 34 degrees) and the direction of a projected trajectory regarding the surface. They also helped locate an estimated descent point in case of the straight flight. On the basis of evidence supplied by eyewitnesses to the joint expedition of the Institute of Solar-Terrestrial Physics and the Irkutsk State University in the villages Mama, Lugovka, Muskovit, and Vitim, as well as reports by the residents of Bodaibo village, we can maintain that the trajectory is well-calculated, reports are consistent with each other and a reconstructed trajectory.
It means that the area, surveyed by the expedition lead by Vadim Chernobrov, is located at least 15 to 20 kilometers southeast of the bolide flight projected upon the surface of the earth, the bolide was flying over the area at an estimated altitude of 30 kilometers. Bearing in mind the modeling physics of meteoroids? entry into the earth?s atmosphere, it?s unlikely that any large fragments might have fallen out in the above area. They must have fallen vertically from 30 kilometers. It?s hard to assume that a horizontal speed had already dropped at that altitude (entry speed ranging from 15 to 25 km/s).
Olga Popova, a researcher at the Institute of Physics of Geosphere, believes that the satellite ?lost? the bolide because the brightness of the latter became lower than the sensitivity threshold of the satellite?s sensors. Numerous eyewitnesses? reports indicate that the bolide kept on flying in the same direction after passing a 30 km border. Detailed reports say that there was no explosion over the area surveyed by Chernobrov?s research party. Upon passing the area, the bolide continued its flight toward the northeast. The real fallout area is located roughly 40 km to the north.
An area of approximately 100 square kilometers with burned and felled trees is reported to have been discovered. The first Vitim expedition picked reports from hunters who visited taiga after the fall of the meteorite and found some parts of the forest damaged, with trees knocked down. Chernobrov?s expedition carried out the survey in the same area. A special study should be conducted to find out when those trees were felled and what exactly knocked them down, a shock wave or gales that blow frequently across that area. Two teams of the second Vitim expedition, organized by the Irkutsk Institutes of Geochemistry, Earth?s crust and Solar-terrestrial Physics of the Russian Academy of Sciences, produced descriptions of the broken treetops and felled trees.
More details of this research will be made available soon. But taking into account that no large fragments of the meteoroid might have fallen out in the above area, and considering the lack of evidence of any explosion, it?s highly unlikely that any trees burned by the bolide will be found. At the time of the bolide flight the sky was fully overcast, it was raining, snow covered the mountaintops, foliage was wet, temperature was recorded at 0 degrees Celsius. The brightness of the bolide was intense, but not strong enough to cause radiation burns on the wood due to low-hanging nimbi (altitude of the rain cloud bottom fringe is about 1100 meters). The brightness diminished dramatically in this area and satellite?s sensors lost track of the bolide forever. We can presume that Chernobrov?s expedition found a burned-out forest, woodlands impacted by a forest fire in the past. Analysis of the fire characteristics on the trees will certainly clarify the issue.
According to Daria Khanukaeva, an expert on meteoric phenomena of the Moscow Institute of Physics and Technics, at a certain altitude a shock wave may deviate from a body in descent due to heavy braking. This phenomenon is most likely to have resulted in a thunderous clap (explosion). In the vicinity of a projected point of deviation ?telegraph woods? (trees with broken branches), and trees felled to the right and to the light of a projected deviation line might be seen.
The impact of a shock wave which broke loose from the meteorite during braking seems the most likely reason for the formation of a zone with felled trees. It seems to be the south side zone. It?s worthwhile to check a symmetrical zone lying in the north. In any case, an area of the hypothetical fallout of the fragments should be located a lot farther to the north and the northeast of the area surveyed by Chernobrov?s party.
Some excitement has been aroused by media reports claiming that the Vitim meteorite was second to the famous Tunguska meteorite in terms of size. Americans estimated the radiation power of the Vitim bolide at the time of its flight as equaling the energy release during the explosion of 200 tons of TNT. As by the Nemchinov model, total kinetic energy of a descending body may equal around 2.3 thousand tons of TNT. It?s simply beyond any comparison to the scale of the Tunguska phenomenon (from 15 to 40 million tons of TNT). The extent of damage is also differs greatly. The Tunguska meteorite caused the burning and felling of the trees on 2200 square kilometers. Considerably smaller portions of the forest near Vitim were partly knocked down by reasons unknown.
According to the calculations performed by Mikhail Nazarov from the Committee for Meteorites of the Russian Academy of Sciences, maximum initial body mass will be 160 tons at a minimal and deliberately understated initial speed of 11 km/s. Because of the charring and approach stream of particles, some 60 tons might have reached the ground, actual amount was smaller that. Given a more probable speed of 25 km/s, about 100 kilos of fragments will make it to the ground. The most optimistic estimations show that the Vitim body measured from 2.5 to 3 meters in diameter on the entry. It?s likely to have been even smaller. It?s far too petty to compete with the Tunguska giant. The Tunguska body has estimated mass of millions of tons, its diameter is thought to be 60 meters. It went off at 5 to 10 kilometers above the earth. The list of meteorites that exploded over the last few years in the atmosphere contain a number of objects that significantly exceed the Vitim body by the energy release.
It?s obvious that all that fuss in the media looks premature. Anyway, practice serves as a criterion for the truth. It would be great if Vadim Chernobrov finds fragments of the meteorite. The American satellite may have acquired wrong coordinates, and a trajectory took a slightly different path, and initial speed may have lead to an extremely heavy breaking, and an explosion occurred high above the earth for all that. However, considering all the available data we find the above scenario pretty farfetched.
At least four professional research parties staffed by scientists from Moscow, Irkutsk, Ekaterinburg and Krasnoyarsk are expected to work in the fallout area in July
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