February 15 near Chelyabinsk thousands of people watched the flight of an unusually bright fireball. His flight was accompanied by strong shock waves, frightened residents and caused the battle of window panes and the destruction of a number of buildings. According to scientists, this decrease in strength of the countryside can be put in second place after the Tunguska event in 1908
However, the science in this case was very lucky. If the Tunguska meteorite fell in the deep remote area of Siberia, almost without witnesses the explosion, here the conditions for fixing the events were almost perfect — a large number of witnesses and a variety of video surveillance. All this has allowed good recreate the picture of the event. In addition, in contrast to the Tunguska event, which has not been found any conventional meteorite, meteorite samples here began to find immediately after passing the car.
According to NASA, power energy released into the atmosphere during the flight of the meteorite was from 0.3 to 0.5 megatons of TNT, or about the power of 20 atomic bombs dropped on Hiroshima. Body weight was in the range 7000 — 10,000 tons, diameter — 17 m, the speed of 18 km / sec., A bright flash occurred at altitudes of 19 — 24 km. Russian scientists have the power and the weight of the body give some conservative values. These data will be refined over time.
Ordinary chondrite meteorite was, however, quite rare type. To date, only a few kilograms of samples collected, mainly centimeter sizes. It can be expected that the snow cover to increase dramatically the number of finds. However, it is clear that the mass of accreted matter, compared to the original mass of the meteorite would be negligible. Chondrites, the well-founded hypothesis considered fragments of the main belt of asteroids located between the orbits of Mars and Jupiter. Mutual collisions and impacts of comets (comet collision with an asteroid knocks him out of the mass of matter is 20 times the mass of the comet) lead to the emergence of a huge number of interplanetary space fragments, one of which, apparently, and became the Chelyabinsk meteorite. Incidentally, it samples clearly visible cracks filled with glass, which is a consequence of the impact of the process.
So where are gone away thousands of tons of meteoritic matter? Let's try to sort out this problem. Of Meteoritics well known that intruded into the atmosphere of the space body has hypersonic speed and prevent excessive ablation — carry-running stream of melt from the surface. Simultaneously with ablation comes into action is another, far more intensive process that destroys the meteorite — is the so-called
. They occur in the boundary layer near the free-stream irregularities and are furiously spinning plasma mikrosmerchi. Vortices literally dig into the surface of the meteorite and drilled grooves on its surface (see Fig. 1 and Figure 2), which in turn contributed to the mass discharge towards small fragments, which are quickly decelerated in the atmosphere and, if not completely evaporate, the meteorites will fall to Earth in the flight path of car. Existing ideas about the destruction of the surface only on the heat, do not correspond to reality
Figure 1. Iron meteorite. Its surface is well etched regmaglypts — frozen traces the impact Görtler.
Figure 2 samples of the meteorite Chelyabinsk. Observed on the surfaces of the recesses can be traces left by vortices Gertler.
Fig. 3 shows a snapshot of flight car. It is clearly seen how the luminosity of the car along the flight path. During the 1.7 seconds it increases sharply and then descends almost to nothing, then only a small glowing wreckage continued their flight. All of the picture indicates that the meteorite is almost completely "melted" in just 1.7 seconds, the flight during which time 30 km. Apparently, the sharp increase in the luminosity of the car due to the advent of Görtler, making the surface glow rose sharply, due to emission from the surface of a large number of fragments of the meteorite. If it had not have vortices Gertler, and acted only ablation, we would have seen a flight brightly luminous point with a small tail, and nothing more.
Figure 3 Still images flying car
Thus, due to an inclined path car (14-200),
the selection of the kinetic energy of the meteorite in the atmosphere occurred at an altitude of about 20 km, for about 2 seconds and trajectory of 30 km, which contributed to the scattering of energy in the atmosphere and only a small part of it in the form of shock waves to reach Earth's surface.
Except considered mechanisms for rapid destruction of the meteorite, there is another option, the so-called mechanism of progressive crushing of the meteorite, the quantitative evaluation which was developed in 1976 by Academician SS Grigoryan. The essence of his idea is that the introduction of a meteorite in the dense layers of the atmosphere in his body, after reaching a certain critical pressure on the front surface, the front of the destruction begins to move at the speed of sound in the solid, which leads to the explosive destruction of the meteorite and its complete evaporation substance. If such a mechanism to function in the body of the Chelyabinsk meteorite, the calculations show that it was a one-off collapse, with the 0085 s, which was not observed. By the way, the Tunguska meteorite, thanks to a mass of 1 million tons and a steeper trajectory (30-400) Penetrated into the lower layers of the atmosphere where exploded at an altitude of 10 km.
If Chelyabinskiy car would also have a steeper path, the destruction meteorite occurred much faster and over substantially closer to the surface that resulted in the isolation of all of its kinetic energy meteorite limited atmosphere. In short, here we have had nearly a clone of a nuclear explosion in a 0.5 Mt of TNT with all its attributes impact on the countryside, with the exception of radiation. Nor can it be ruled out that due to the sharp increase aerodinamicheskog
As is known, the flight was accompanied by a powerful car train. (See Figure 4), which, given its large angular size and location
Fig. 4. A fresh plume of flight car
Figure. 5 shows a photograph of the loop in the final stage of its scattering. The picture shows clearly that it was a dark color. This indicates that the steam fraction cloud disappeared and were only microspherules — solidified melt drops meteoric substance. The large angular size of a dark tail also points to his impressive mass. In short, there is clearly presented, in which, in the end, turned Chelyabinsk meteorite.
Fig. 5. The final phase of the scattering loop
Great interest to science are finding meteorites and determining areas falling on the ground microspherules. To collect meteorites best time — this is the end of snow cover. When the thickness of the snow will be a few centimeters, the dark meteorites are clearly visible in the snow, and sun areas, they will be in the snow pits formed by thermal radiation heated the meteorite, which will increase the probability of detection. Especially this phenomenon will occur around the meteorite weighing more than 1 kg. Collecting meteorites keep the car under the flight path. Maybe eventually manage to get the total mass of the meteorite has fallen to the ground substance. To identify areas of scattering microspherules can benefit from the rich experience gained by researchers of the Tunguska meteorite.
The nature of meteorites falling Chelyabinsk gives some hope yet to discover fragments of the Tunguska comet. The fact that the motion Tunfuska body before reaching the height of about 10 km occurred, apparently scenario Chelyabinsk meteorite. Further, due to its huge mass (~ 1 million tons), he has kept a high speed, and when at a height of about 10 km the pressure on its front surface exceeds the critical pressure, load mechanism of progressive crushing and meteorite exploded, leading to the complete evaporation of its substance.
Knowing these flight characteristics of the Tunguska body, the author in his works repeatedly called field researchers to search for dropped objects under the flight path of car. However, despite the fact that it is under the flight path near the epicenter was found small impact crater with a set of space particles, his appeal has remained unheeded.
In conclusion, it must be said that the local people due to the flat trajectory of the Chelyabinsk car, you can say lucky, so they are obliged every year to mark the date of February 15, no more, no less, as the "Day of the Meteorite" and be thankful for their wonderful salvation from a cosmic catastrophe.
March 30, 2013 | Eugene Dmitriev