Meteorites leave scars on the planet

30.03.2013


When a meteorite from outer space speed crashes into a solid surface of the planet, there is a powerful blast of heat, and in its place in a matter of seconds formed a special geological formation — a meteor impact crater. Major clashes of this kind could cause mass extinctions of species in Earth's history. However, recent studies suggest that the origin of life could be associated with impact craters.

The surface of the Earth would look like a real testing ground for the bombing, pitted with numerous craters of different sizes, not whether it is protected by a gas shell. The collision of Earth with a large celestial bodies kilometer diameter occur on average once in a million years. The particles of the same size from dust grains to a small rubble piled on the planet almost continuously. Flying into the atmosphere at a rate of tens of kilometers per second, they are heated by friction with the air and burn up before reaching Earth's surface. Such is the fate of more than 99% of space debris. Only the largest of them reaches the surface, forming craters that are relatively rapidly destroyed by erosion. Therefore, on this planet do not know too many impact craters — a total of about 170.

Another thing is the moon, where there is no atmosphere. Its surface is completely covered with craters with a diameter from a few centimeters to hundreds of kilometers. The vast majority of them are very old. More than 4.5 billion years ago from the dust and rocky debris orbiting the sun, there was a formation of planets and satellites. The particles gradually coalesced into large chunks, and the surface of the protoplanetary fell all the new pieces. This lasted until about 4 billion years ago, a swarm of debris has not subsided. Numerous lunar craters — is evidence of the last phase, called the "intense bombardment".



 

In the Sea of Crises lunar craters almost there. It turned out that in the ancient lunar craters were formed very often, and then for a short time — from 4 to 3.8 billion years ago — the frequency of falls of meteorites fell a thousand times and since then has remained roughly constant. Photo: SPL / EAST NEWS

Space drummers

Meteor or shock-blasting, craters — is the most common form of relief to many of the planets and moons in the solar system and even on such small objects like asteroids. On our planet, the average speed during meteor impacts is about 20 km / s, and the maximum — about 70 km / s. At a meeting of the meteorite with its solid surface movement slows down sharply, but the target species (the so-called the place where he fell), on the contrary, begin accelerated motion under the influence of the shock wave. It radiates in all directions from the point of contact: hemispherical covers the area under the surface of the planet, as well as moves in the opposite direction by the very meteorite (drummer). Reaching its rear surface, the wave is reflected and runs back. Tension and compression in this double mileage usually completely destroy the meteorite.

The shock wave creates a lot of pressure — more than 5 million atmospheres. Under the influence of the rocks of the target and projectile are strongly compressed and heated. They are partially melted, and in the center, where the temperature dosgigaet 15,000 ° C, — even evaporate. In this melt and solid debris fall of the meteorite. As a result, after cooling and solidification at the bottom of the crater formed by a layer of impactites (from the English impact — blow) — rock with very unusual geochemical properties. In particular, it is very strongly enriched in extremely rare on Earth, but more characteristic of the chemical elements of meteorites — iridium, osmium, platinum, palladium. This is the so-called siderophile elements, that is, belonging to the group of iron (in Greek — sideros).

The flashing of the material leads to an explosion in which the target species fly in all directions, and the bottom is pressed. There is a circular depression with fairly steep sides, but there is a fraction of a second — and then the board will immediately begin to fall in and slump. On top of this mass of soil drops and hailstones of material ejected vertically upwards and are now returning to the place, but in a fragmented way. So at the bottom of the crater formed breccia — a layer of rock fragments cemented with the same material, but crushed to sand and dust.

Clash, the compression of rocks and pass the blast last tenth of a second. The formation of the recess of the crater is an order of magnitude more time. A few minutes later impact melt breccias hidden under a layer begins

quickly
harden. And now ready to fresh, piping hot, the impact crater.

With strong collisions solid rock behave like a liquid. They raise complex wave hydrodynamic processes, one of the characteristic signs of which — in the central peaks of large craters. The process of their formation is similar to the appearance of a drop impact if dropped in the water of a small object. Strong impact material ejected from the crater can even fly into space. This is how the Earth came from the moon and meteorites from Mars, dozens of which are found in recent years.

Arizona calculator

The size of the resulting crater depends on the speed and angle of incidence of the impactor and the target (or iron meteorite stone, rocks or loose on the planet), and the force of gravity on the surface of the celestial body. For example, at the same impact energy on the half moon crater formed larger in diameter than the world.

In one of the leading centers in the world planetologicheskih — Lunnoplanetnoy Laboratory of the University of Arizona in Tucson have created an online calculator to calculate the consequences of a fall to earth of a large meteorite or asteroid (www.lpl.arizona.edu / impacteffects). Among other things, this calculator calculates the size of the resulting crater and the impact on the observers, who are at a distance from the crash site. It's fun to use it to evaluate the information reported in the news about the possible consequences of a falling object.

Characteristically, for the small size of the meteorite Arizona refuses calculator to estimate the size of the crater. A small piece of space or completely burn up in the air, or lose speed and fall, like a simple stone. In the latter case, on the surface, of course, there will be a pothole, but it is very different from the shock of the explosive crater on Earth that can not be less than a few hundred meters. For other planets it depends on the density of the atmosphere. For example, on Venus, with its extremely dense gas shell minimum diameter of the crater — more than a kilometer, and on to the surface of Mars with almost no loss of speed and reach the outskirts small meteorites forming ten-sized craters. On celestial bodies, deprived of the atmosphere, for example, on Mercury, the Moon and many other satellites of the planets, craters generated by meteorites of all sizes and can even be a centimeter.



 

Earth — Manicouagan crater. Legend of the pinched arteries. Photo: SPL / EAST NEWS

Passengers flying from Europe to the Canadian Montreal may notice expanses of boreal Labrador unusual lake. On a dark background coniferous forest stands well water ring, covering all sides is huge, with a diameter of 70 kilometers, the island is also covered by forest. This ring structure Manicouagan — one of the oldest among the currently known impact craters, or rather, his trail. The fall of the meteorite diameter of five kilometers happened here 214 million years ago. On Earth, then ended the Triassic period, and just appeared dinosaurs. However, this disaster on them, it seems, had no effect, because the next 150 million years, they literally dominated the planet. Much later, the crater "crawled" the huge glacier that cut off the top layer of rock in a kilometer thick, but the central part of the bottom of the crater succumbed to glacial erosion, as a member of the "cake" is very hard rock that emerged during the melting of the moment of impact.

Thus was formed a plateau, surrounded by a valley through which the river flowed. In 1968, the river was blocked Manicouagan hydroelectric dam, and it flooded the valley, the envelopes of the plateau on both sides. There was a ring the lake, and the plateau was an island — the second largest in the world among the islands in the lakes. Its area — 2040 km2 — almost 100 km2 larger than the area of the Lake Manicouagan, in which it is located. René-Levasseur Island is named after the engineer who supervised the erection of seven years, the dam of the hydroelectric power station — and the fifth largest in the cascade on the Manicouagan River. Open it, he had shared with the Prime Minister the Canadian province of Quebec, Daniel Johnson, in the past too hydropower. But on the eve of the planned opening Levasseur died suddenly of a heart attack at the age of 35 years. A few days later, the same fate befell the arrival ceremony at the start GES Daniel Johnson, who was 53 years old. The island was named in memory of the engineer, the dam — in honor of the prime minister, and in the legends of the Innu Indians, Alaska Labrador taiga, a version that both the main creator of the dam have died because of the nature of the blood arteries pinch them in revenge for what they clamped her water artery, building on the Manicouagan River a cascade of hydropower plants.

Dangerous maneuvers asteroid

Large meteorites forming an impact crater on Earth, fall is extremely rare. However, it is possible that in less than 30 years of earthlings are going to witness such an event. Open only five years ago, an asteroid Apophis is small on a cosmic scale. Its exact size has not been determined, but is estimated to be 300-400 meters. It would not cause concern if his path does not lay dangerously close to Earth. According to the calculations of astronomers, every 1300 years this asteroid for several decades is far away from our planet, and with it comes a series of fairly close encounters with intervals of about 5-10 years, after which the celestial path of the Earth and the asteroid again for a long time apart.

In 2029, Apophis will pass at a distance of about 33,000 kilometers from Earth. However, the impact of the gravitational field of the planet can change the orbit of Apophis so that at the next meeting, in 2036, it will be even closer and maybe even collide with the Earth.

Calculations performed on the basis of current, accurate data is not enough on its motion, show that the fall in 2036 can occur in a narrow band width of a few tens of kilometers, extending from northern Kazakhstan through Siberia to the Magadan, Kamchatka further from the Pacific Ocean to Nicaragua to the north of Colombia and Venezuela, and then the Atlantic Ocean to the west coast of Africa.

In a populated area will lead to the fall of total destruction in a radius of 100 kilometers from the point of impact. There will be a crater several kilometers, and will be thrown into the stratosphere significant amount of dust that significantly reduce solar heat gain in the whole earth. In the case of a drop in the ocean, even away from the coast, there will be strong tsunami that will destroy all the coastal cities.

The Planetary Society of the United States, whose headquarters is in California, not far from the coast of the Pacific Ocean have been carried out in 2008 a competition to design anti-collision with Apophis. It was timed to coincide with the centenary of the Tunguska event, which remains the largest invasion from outer space, occurred in the memory of mankind.

Among the projects of protection from an asteroid — high-speed impact of the metal "blanks" weighing a ton, a nuclear explosion on the surface of the asteroid, painting its surface, so that the orbit has changed under the influence of solar radiation pressure and the "gravity tractor", which hangs above the asteroid with working ion engines thrusters and gradually shift it to the new orbit its gravitational pull.
 

But to begin to Apophis, will most likely be sent to a small automatic station, which take pictures of his face, will study the gravitational field, which helps to assess the internal structure of the asteroid, and most importantly — it will reset the beacon to accurately track its trajectory from the Earth. This relatively inexpensive project of American engineers took first place in the competition Planetary Society. Only then refine the asteroid will be possible to plan the correction of its trajectory. After all, the worst thing that can happen — it's hurry up and push the asteroid in the wrong direction, right on our planet.


Moon — Tsiolkovsky crater. Dark eye on the nape of the Earth satellite. Photo: SPL / EAST NEWS

One of the most picturesque among the tens of thousands of lunar craters called the Tsiolkovsky. Name Kaluga teacher of physics and mathematics, which became the founder of the theory of interplanetary travel, appeared on the map of the moon in 1959, when with the help of one of the first "honesty" — automatic station "Luna-3" — was first photographed the reverse is never visible from the side of the Earth our satellite. This required to fly around the Moon, and then pass the pictures on the radio, using about the same apparatus as that of the modern fax machines — the image is automatically divided into different points of brightness, which were built line by line. The resulting images of half a century ago are not very definition, but two stood out dark details on them very well. They are contrasted with bright terrain, occupying almost the entire side of the moon. A larger one called Sea of Moscow, and one that is less — Tsiolkovsky. This crater with a diameter of 180 kilometers is located in the southern part of the reverse side of the Moon, and serves as an excellent reference on lunar maps and flight around the moon.

The fact that it is located inside the frozen lake of black lava, the center of which stands a bright spot slide, characteristic of large impact craters. On the back side of the Moon has no large dark plains — the lunar maria, as the crust is thicker there than on the near side, and it was hard to get through the magma from the depths to the surface. In the area of Tsiolkovsky thickness of the lunar crust is almost a record high — 75 kilometers, so to think that the formation of the impact of a meteorite crater was particularly strong — perhaps it occurred at a very high speed, and the crack under the crater penetrated very deeply into the bowels of the moon, reaching layer of magma. From there, basaltic melt was poured onto the surface of the cup and half flooded crater formed after curing plain black, which is similar to the central mountain island with steep banks. As a result, the entire shape of the crater became dark eyes with a bright pupil, and his gaze directed billions of years in the space provided, on which research with the help of "reactive devices," Konstantin Tsiolkovsky thought in the nineteenth century, created in 1896, when he was only 39 years old, mathematically rigorous theory of jet propulsion.

Riches "star wounds"

Back in the late XVII century English astronomer Edmund Halley suggested that comets may fall to Earth, causing a global catastrophe similar to the biblical Flood. He even thought that from such a collision occurred Caspian Sea basin — in those days the Caspian depicted on the maps in the form of a circle, resembling a giant crater. However, such ideas were nothing more than speculation, while on earth did not detect the actual evidence of such disasters. Usually this is not depression relief, as the moon, and the ring structures, which are traces of former craters, almost erased from the surface of the Earth an active geological activity, primarily by water erosion. Geologists call them Astroblems, which translated from Greek means "star wounds".

In places the fall of celestial bodies on the Earth are often formed by a variety of mineral deposits. And in the field Astroblems are unique in size and mineral composition. Thus, in the north of Siberia in Popigai crater 100 km in diameter found diamonds formed during meteorite impact in rocks containing graphite. Many astrobleme are industrial sources of ore, for example, about half of the nickel produced in the world due to the deposit of Sudbury, Ontario. It is believed that the oval in terms of geological structure measuring 60 × 25 km, which is being produced, formed in the distant past, in the fall of a large meteorite. Along with nickel in Sudbury extract also more expensive platinum group metals, copper, cobalt, selenium, tellurium, gold, silver. These items were not recorded on the Earth meteorite.

The tremendous explosion led to cracking of the subsoil to a greater depth, and thence along the faults began receiving material that formed the ore field, which is considered one of the richest in the world.

Among the largest and oldest astroblems probably refers Middle Ural circular structure with a diameter 550 kilometers. The eastern part of the shaft of this structure is clearly expressed in the form of a rather sharp bend arcuate middle portion of the Ural mountain range, which as a whole is almost due north to south. The vast majority of the Ural mineral deposits is concentrated in this arc, the lowest part of the Ural Mountains, called the Middle Urals. Mined here, and is still mined iron, copper, chromium, nickel, titanium, uranium, gold and other metals are also concentrated deposits of gold and famous gems. The deposits are associated with fractures in the Earth's crust, resembling a giant outline astroblems. These faults and serve as "leading out channels" for the receipt of ore material from the depths of the Earth's interior. The inner part of this huge crater slowly filled with sediments, which have the oil fields of the Volga-Kama region.

Apart form astrobleme stand "foreignness" of the geological structure in relation to the surrounding area. Rocks exposed in the formation of the crater are very different in age and on the geological map can be seen as a kind of splash. Different landscapes and formed on the sites of former craters — against the background of a uniform steppe or taiga regions attract attention with a concentric arrangement of the river network, vegetation, soils, as can be seen in satellite images. That's why with the advent of satellites, conducting survey of the planet, dramatically increased the number of detected traces of ancient meteorite.

Tests of prototype vehicles and Martian meteorite crater in suits on the Canadian Devon Island (artificial color). Photo: HAUGHTON-MARS PROJECT / P. LEE

The disaster in the Yucatan

If 65 million years ago, someone could take a look at the Earth from the side, he would have seen over the area of the current Mexican Yucatan peninsula grand explosion, emission in the near-Earth space is a huge mass of material in the form of a giant funnel. According to many researchers, then our planet is faced with an asteroid that occurred about 10 kilometers across. In the Earth's atmosphere, he broke into fragments that are falling on the surface of the planet, made a terrible destruction. The explosion burned the colossal power of all life in the region, has caused an earthquake, hurricane, tsunami wave of up to 100 meters and related flooding. Clouds of dust, smoke, ash and steam enveloped the entire Earth, eclipsing the sun for a few years have passed acid rain. There was a long-term cooling. This caused a massive loss of many species of plants and animals. Some scientists believe that such disasters have occurred many times in Earth's history.

The picture of this disaster is recreated on the results of the study are very large, with a diameter of 180 kilometers, the crater, which is located on the northern tip of the Yucatan Peninsula. The name of this giant crater was located on almost in the center of a small settlement Chikshulub. Despite such a large size of the crater, it was discovered only 30 years ago. The fact that it is covered with a thick layer of geological strata, and also on the land is only southern half of the crater and the remaining part is located offshore, and in addition sediment still hidden Gulf of Mexico. Gravity survey yielded an image of the ring structure inaccessible to direct observation.

The time of formation of the crater correspond to clay deposits in which the content is extremely rare on Earth iridium is 15 times higher than the background. This iridium layer just serves as a boundary marking the end of the Cretaceous geological period, for which the typical fossils of dinosaurs. In more recent sediments of them almost never caught. Hence, it has been suggested that the extinction of these giants, and so many more species of fauna of the Cretaceous period, caused the change of climatic conditions caused by the fall of a giant meteorite crater Chikshulub. However, it should be noted that, from this point of view, not everyone agrees paleontologists.



 

Mars — Tikhonravov crater. Why do not they fly? Photo: SPL / EAST NEWS

In the name of rocket designer Michael Klavdievich Tikhonravova (1900-1974) named one of the largest craters on Mars — the diameter of the 380 kilometers. It was formed in the earliest period of the geological history of the Red Planet, and since then his ample bottom fell several large meteorites, which left craters with a diameter of tens of kilometers. The result is a messy picture, it is typical for the location of impact craters scattered randomly. The additions to the landscape and made the Martian atmosphere, which is known for strong dust storms lasting for weeks — sometimes they hide from view the entire surface of the planet. Although the winds in the rarefied atmosphere of Mars is weaker than on Earth, they still carry away the worn thousands of years of erosion Martian sand, which is much smaller than typical terrestrial.

The shafts of smaller impact craters, towering over even the bottom of a vast crater Tikhonravov, are barriers in a collision with which the wind becomes invalid. Portable sand they remain near the crater, where gradually formed dunes and dune fields. The dark color of these sands are required high content of iron compounds. Sometimes a combination of craters and dunes can see funny pictures, as in this picture, where two adjacent craters of the same size together with complementary them "eyebrows" dark dune fields create the full experience the surprised faces, contours of which is the shaft of a giant crater.

The man, whose name is now this crater, launched its first rocket in 1933, and later headed the design bureau SP Queen of the development plan of the expedition to Mars. Prior to that he had "a hand" and the first artificial satellite of the Earth, and to Gagarinskoe "East", and to the automatic interplanetary stations. Designed by him in 1962 for a manned flight to Mars heavy spaceship abbreviated as TMC, which by some coincidence, coincided with the initials of the designer. However, the Martian expedition was planned at that time to 1974, did not materialize, and its future is very vague. Maybe this is what is surprising in a Martian spacecraft designer namesake?

Meteorite incubators

Recent studies have shown that, probably, impact craters, meteorite crater, were those oases where arose and began to develop life on our planet. The US-Canadian research team worked for several years in the meteorite crater Houghton on Devon Island in the Canadian Arctic. This crater with a diameter of 24 kilometers is well marked in the landscape. In cold arctic desert there is almost no vegetation, which facilitates exploration. In addition, the terrain and climatic conditions are to some extent reminiscent of Mars, so just inside the crater were installed light-frame tent cabins unusual cylindrical shape that mimic base on Mars. Here are tested prototypes suits and vehicles on the surface of Mars — four-and six-wheeled "marsotsiklov", each of which can go to one person. It is in the vicinity of semi settlements and discoveries have been made, which allowed for a fresh look at the role of impact craters in the origin and evolution of life.

Canadian Space Agency geologist Gordon Osinski, carefully analyzing the minerals from the rocks that form this crater, found that 23 million years ago in the explosion that formed the crater, there was a network of deep cracks through which from the depths to the surface began to receive hot water with dissolved salts . After tens of thousands of years, the temperature of the geothermal decreased so that they could live microorganisms. Depression of the crater itself also contributed to the creation of favorable conditions for life, protecting it from external influences and concentrating the sun's heat for its slopes. In the crater lake appeared, which lasted a long time, and now the layers of sediment accumulated on the bottom of it, serve as evidence of the changes that have taken place on our planet in the past. Hydrothermal products are generally considered favorable place for the development of life, and that their traces are found in many impact craters.

On what planet these craters are the most interesting objects that could potentially be stored traces of past life. First of all, it refers to Mars, where the search for traces of life would be best to keep inside impact craters.

Previously, it was believed that their education should lead only to such changes in the environment that cause mass extinctions, the new view shows the opposite: impact craters could be comfortable habitat for living organisms, especially in the cold regions of the globe. According to modern ideas, life appeared on Earth about 3.8 billion years ago — just at a time when over intense meteorite bombardment craters and covered with an abundance of young surface of the planet. Maybe they were cozy "nest", but rather "aquarium" for the first inhabitants of the Earth.

George Burba

 

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