February 15, near Chelyabinsk, thousands of people watched the flight unusually bright car. His flight was accompanied by strong shock waves that frightened the inhabitants and caused the battle of window panes and destruction of a number of buildings. According to scientists, this drop in strength impact on the terrain can be put in second place after Tunguska catastrophe of 1908
However, science in this case was very lucky. If Tunguska a meteorite fell in a remote inaccessible region of Siberia, practically without witnesses to the explosion, here the conditions for fixing the event were almost perfect – a large number of witnesses and a variety of means video surveillance. All this allowed to recreate the picture well. event occurred. In addition, unlike the Tunguska disasters where not a single traditional meteorite was found, here, meteorite samples began to be found immediately after the flight car.
According to NASA, the power of energy released into the atmosphere at the meteorite’s flight ranged from 0.3 to 0.5 megatons of TNT, which corresponds to approximately the power of 20 atomic bombs dropped on Hiroshima. Body weight was in the range of 7000 – 10000 tons, diameter – 17 m, speed 18 km / s., A bright flash occurred at altitudes of 19 – 24 km. Russian scientists on the power and body weight give several underestimated values. The data will be over time to be specified.
The meteorite turned out to be ordinary chondritis, although quite rare type. Today, a few kilograms of samples have been collected, in mostly centimeter sizes. It can be expected that at the gathering snow cover the number of finds will increase dramatically. However already it’s clear now that the mass of the precipitated substance, compared with the initial mass of the meteorite will be insignificant. Chondritis, by a well-founded hypothesis are considered fragments of asteroids the main belt located between the orbits of Mars and Jupiter. Collisions and impacts of comets (comet in collision with asteroid knocks out a mass of substance from it 20 times higher mass of comet) lead to the appearance in interplanetary space a huge number of fragments, one of which, apparently, became Chelyabinsk meteorite. By the way, in his samples are clearly visible cracks filled with glass, which is a consequence of shock process.
So where did the thousands of tons of meteorite matter go? Let’s try sort out this problem. From meteoritics it is well known that the cosmic body intruding into the atmosphere has hypersonic speed and will undergo severe ablation – ablation a stream of melt from its surface. Along with ablation in another, much more intense process comes in, a destructive meteorite is the so-called Gertler’s vortices. They arise in boundary layer of the oncoming flow near irregularities and represent furiously rotating plasma microsmerches. Whirlwinds literally dig into the surface of the meteorite and drill recesses on its surface (see Fig. 1 and Fig. 2), which, in its the queue contributes to mass ejection towards small fragments that are quickly inhibited in the atmosphere and, if fully do not evaporate, they will fall by meteorites to the Earth along the trajectory flight car. Available understanding of surface degradation only from heating, do not correspond to reality, because due to low thermal conductivity of a stone meteorite, it does not have time in seconds bask deeply, especially since the surface layer is intensely updated by ablation.
A photo from open sources
Fig. 1. Iron meteorite. On its surface is good the regmaglipts were captured – frozen traces of the effects of vortices Görtler.
A photo from open sources
Fig. 2 Samples of the Chelyabinsk meteorite. Observed on the surface of the recess may be traces left by vortices Görtler.
In fig. 3 shows a still image of a car race. Clearly see how the luminosity of the car changes along the flight path. Within 1.7 sec, it increases sharply and then almost disappears, after whereby only small luminous debris continued its flight. All the picture indicates that the meteorite is almost completely “melted” in just 1.7 seconds, flying 30 km during this time. A sharp increase in the luminosity of the car is apparently associated with the appearance of Görtler vortices, due to which the surface of the glow increased sharply due to emissions from the surface of a large meteorite number of fragments. If there were no Görtler vortex, only ablation acted, then we would observe the flight brightly a luminous dot with a small tail, and nothing more.
A photo from open sources
Fig. 3 Freeze frames of a car flight
Thus, thanks to the inclined path of the car (14-200), the release of kinetic energy of a meteorite in the atmosphere occurred on at an altitude of ~ 20 km, over ~ 2 sec and on a section of a trajectory of 30 km, which contributed to the dissipation of this energy in the atmosphere and only a small part of it in the form of shock waves reached the surface Of the earth.
In addition to the considered mechanisms of rapid meteorite destruction there is another option, the so-called progressive crushing mechanism meteorite, a quantitative assessment of which was developed in 1976 academician of the RAS S.S. Grigoryan. The essence of his idea is that when a meteorite is introduced into the dense layers of the atmosphere in its body, after reaching some critical pressure on the frontal surface, the front of destruction begins to move, with speed sound in a solid, which leads to explosive destruction of a meteorite and the complete evaporation of its substance. If such a mechanism acted in the body of the Chelyabinsk meteorite, then calculations show that it should was destroyed once, for 0085 seconds, which was not observed. By the way, the Tunguska meteorite, due to its mass of 1 million tons and a steeper flight path (30-400) penetrated into the lower layers atmosphere where it exploded at an altitude of 10 km.
If the Chelyabinsk car would also have a steeper trajectory, the meteorite destruction occurred much faster and ended substantially closer to the surface, leading to the release of all its kinetic energy meteorite in a limited volume of the atmosphere. In short, here we had almost complete 0.5 mt TNT nuclear explosion analogue with all its attributes impact on the terrain, with the exception of radiation. Also exclude that due to a sharp increase in aerodynamic pressure on a meteorite – and such a process is similar to a hit – it is quite possible the mechanism of progressive meteorite destruction by Grigoryan, which further aggravated the situation. Now let’s see, in what turned Chelyabinsk meteorite.
As is known, the flight of a car was accompanied by a powerful train (see Fig. 4) that, given its large angular dimensions and location at an altitude of 20 km, may indicate its huge mass. In other words, we observe an extended gas-dust cloud – trace of meteorite material recovered. Cloudy view of a plume could give vapors and particles of both the meteorite itself and nitrogen oxides air that invariably forms at high temperatures. That that the meteorite during intensive braking was not divided into parts, talk about its high bulk strength, i.e. in his body there were no large cracks, and it apparently was monolith.
A photo from open sources
Fig. 4. Fresh train from the flight of the car
In Fig. 5 is given a photograph of the plume at the final stage of its scattering. The picture clearly shows that it has become dark in color. This indicates that the vapor fraction of the cloud has evaporated, and remained, only microspherules – frozen drops of melt meteorite substance. Large angular dimensions of the dark loop so indicates its impressive mass. In short, here clearly presented in what, in the end, turned Chelyabinsk meteorite.
A photo from open sources
Fig. 5. The final phase of the scattering of the loop
Of great interest to science are finds of meteorites and determination of zones of precipitation of microspherules on the soil. To collect meteorites the most favorable time is the end of the snowfall cover. When the thickness of the snow will be several centimeters, then dark meteorites will be clearly visible in the snow, and on sunny areas, they will lie in the snow holes formed from thermal radiation of a heated meteorite, which will further increase probability of their detection. This phenomenon will especially manifest itself. around meteorites weighing more than 1 kg. Collect meteorites under the flight path of the car. Maybe, over time, manage to get the total mass of meteorite falling to the ground. For identify microspherical scattering zones can take advantage of the rich experience gained by researchers of the Tunguska meteorite.
The nature of the precipitation of Chelyabinsk meteorites instills a certain hope to discover the fragments of the Tunguska comet. The thing is, that the movement of the Tunguska body, until it reaches a height of ~ 10 km apparently occurred according to the scenario of the Chelyabinsk meteorite. Further, thanks to its huge mass (~ 1 million tons), it retained high speed, and when at an altitude of ~ 10 km the pressure on its frontal surface exceeded critical pressure, mechanism worked progressive crushing and meteorite exploded, leading to complete evaporation of its substance.
Knowing these features of the flight of the Tunguska body, the author in his has repeatedly called on field researchers to search dropped objects under the flight path of the car. However, despite that it was precisely under the flight path near the epicenter that a small impact funnel with a whole set of space particles, his call was never heard.
In conclusion, I must say that the locals thanks a gentle flight path of the Chelyabinsk car, we can say lucky and therefore they are simply obliged to celebrate every year date February 15th, no more, no less, like “Meteorite Day” and thank fate for your miraculous salvation from space disaster.
March 30, 2013 | Evgeny DMITRIEV
Time Chelyabinsk
