Meteorites
FROM HISTORY
Meteorites. These space wanderers have long stirred the hearts of people. Looking at the night sky overhead, each of us has at least once seen how one of the stars breaks from its place and falls rapidly, tracing a bright trail in the sky. Imagine how surprised people were centuries and thousands of years ago when a meteorite fell before their eyes. Thunderous rumble, hissing and cracking, a fireball sweeps across the sky and falls with an incredible roar! The memory of this event became legends and myths, and people kept fragments of the heavenly stone as sacred relics. It is not surprising that even scientists for a long time refused to recognize meteorites as reality, considering the stories about them fiction. It is only with 1794 studies of the Pallos iron, a large meteorite found in Siberia, that they were able to confirm the extraterrestrial origin of these objects.
More than two hundred years have passed since then, and today meteorites are under the close attention of experts from various branches of science. Meteorites have become a part of world pop culture. They appear in films and science fiction novels. It is time for us to finally find out what these guests from outer space are.
WHAT IS A METEORITE?
In addition to planets and stars, there are many different objects in space. There are asteroids – bodies similar to planets, but not so huge. Asteroids have their own orbits around the Sun, while some of them even have satellites. There is also dust – the smallest particles of matter dispersed in outer space, and there are intermediate objects of medium size. Their sizes range from 0.1 mm to 10-30 m. They are called meteoroids. They can be dispersing into space, moving along arbitrary trajectories, or have relatively stable orbits. Sometimes there is a whole cluster of meteoroids – the so-called swarm.
When such a meteoroid enters the gravitational field of the planet, its trajectory changes, and it gradually rushes to the surface of the planet. Occasionally there are collisions of the planet with asteroids.
A colorful phenomenon in the form of a cosmic body burning in the atmosphere is called a meteor (or fireball).
Only when a cosmic body (no matter what size) reaches the surface of the planet, it can be called a familiar term – a meteorite.
WHAT ARE METEORITES?
Of course, every meteorite is unique and no two meteorites are the same. However, depending on the structure, they are divided into three large groups.
Stone meteorites. This is the largest group. 92.8% of all meteorites reaching the earth are stone, and 92.3% of them are known as chondrites. Surprisingly, their composition is identical to the chemical composition of the Sun, with the exception of light gases, hydrogen and helium. How is this possible? The solar system has formed from a giant interstellar gas-dust cloud. Under the influence of gravity, matter rushed to the center, forming a protostar. Under the influence of the mass of matter falling on it, the temperature of the protostar increased and, as a result, thermonuclear reactions broke out in its center. This is how the Sun was born, while the remnants of substance from the gas-dust cloud formed all the other space objects of the Solar System. Chondrites are those smallest particles formed from the substance of a gas–dust cloud. We can say that both the chondrites and the Sun are made of the same material. The main minerals in their composition are various silicates.
All other meteorites have a complex origin and represent fragments of asteroids or planetary objects. Some of them are stone, like chondrites, but their composition and structure are different.
Metal meteorites are another large group, accounting for 5.7% of the total number of meteorites hitting the ground. They mainly consist of an alloy of iron and nickel, which make them very solid and almost not susceptible to corrosion.
Finally, the rarest (and most beautiful) meteorites are ironstone. They make up only 1.5% of total, but they have a complex structure in which the metal part is intertwined with silicate formations.
Meteorites:
1)Iron
2)Stone
3)Ironstone
HOW MANY METEORITES FALL TO THE EARTH?
About 5-6 tons of meteor substance fall to the earth per day. This is about 2 thousand tons per year. It might seem a solid figure. However, most meteorites burn up in the atmosphere before reaching the ground. A significant part of the rest falls into the ocean or sparsely populated areas – simply because they occupy most part of our planet. Only in rare cases does a meteorite fall in a populated area, in the sight of people.
WHAT HAPPENS WHEN A METEORITE FALLS?
Cosmic bodies move at tremendous speeds. When entering the atmosphere, the speed of a meteorite can reach 11 to 72 km/s. From the friction of the air, it lights up and begins to glow. As a rule, most meteorites burn up before reaching the surface of the earth. A large meteorite gradually slows down and cools down. What happens next depends on many factors. Among them mass of the falling object, initial velocity, angle of entry into the atmosphere. If the meteorite manages to slow down, its trajectory may change to an almost vertical one and it will simply fall to the surface. Sometimes the internal structure of a meteorite is heterogeneous, unstable. In this case, it explodes in the air, and its fragments fall to the ground. This phenomenon is called a meteor shower. However, if the speed of the meteorite is still high (about 2-4 km/s), and the meteorite itself is quite massive, a powerful explosion occurs when it collides with the earth's surface.
A meteorite crater – an astrobleme - is formed at the site of the fall of a large meteorite. On Earth, such craters are not always visible because of weathering and other geological processes, which destroy them, but on other planets, you can see traces of colossal meteor bombardments.
There are meteorite craters on the territory of Russia as well. The largest of them is located in Eastern Siberia. This is the Popigai crater, its diameter is 100 km, and it is the fourth largest in the world. Popigai was formed 35.7 million years ago as a result of a collision of a large asteroid with the Earth. There is evidence that diamond deposits are hidden in its depths, but the detailed information about this was classified back in Soviet times. The oldest of the Russian craters (and one of the oldest in the world) is the small crater Suavjarvi in Karelia. Its diameter is only 3 km, and now there is a lake in it. However, the age of the crater, reaching 2.4 billion years, is impressive.
THE DANGER OF METEORITES
The chance that a meteorite will hit a person is negligible. In total, there have been two reliable cases of a meteorite hitting a person, and both times people received minor injuries. In addition, over the past two centuries, there have been about a dozen testimonies of people dying from a meteorite strike, but they had no official confirmation.
Nevertheless, it would be unwise to deny the danger of meteorites. The example of the Chelyabinsk meteorite shows that even an indirect impact from the explosion of a large space object can be devastating.
There is a stereotype in popular culture that meteorites can be radioactive, or that they are carrying spores of some monstrous alien diseases. These modern myths are supported by fiction and cinema, but they are groundless. There were no cases of radioactive meteorites detection. Not a single one.
In order for a piece of stone or meteorite to be radioactive, it must contain radioactive substances. For example, uranium. Still, over time their radioactivity decreases. The rate of deсline in radioactivity is characterized by a physical quantity known as half-life period. This figure is much smaller than the average age of any of the meteorites falling to Earth.
There are still sources of radiation in space, for example, the sun, aren’t there? Yes, but it should be understood that being irradiated does not mean becoming radioactive. If you spend the weekend in a nuclear reactor, you are unlikely to feel well afterwards. Nevertheless, you would not emit radiation.
Some meteorites contain complex organic compounds, and this is the reason why they are of great interest to scientists. However, neither microorganisms nor traces of alien life have been found on meteorites yet.
WHAT ARE METEORITES USED FOR?
In ancient times, meteorites could serve as objects of religious worship. Meteoritic iron was known long before people learned how to melt iron from ore on their own. Products made of meteoritic iron were highly valued. One of the examples is a dagger found in Tutankhamun's tomb.
Today meteorites are largely of scientific interest. They can tell a lot about the young days of our Solar system and about distant worlds.
Nevertheless, iron and ironstone meteorites are used in jewelry art. The crystal lattice structure itself gives them a unique beauty: intertwining crystals needles, complex geometric shapes, fractal compositions. In scientific terms, such a phenomenon is called Widmanstatten figures. They are formed during a very slow process of cooling of an iron-nickel alloy heated to incredible temperatures. There is no air in space and no heat carrier, so the meteorite cools down for an infinitely long time – by several degrees in one million years. In ironstone meteorites, an amorphous metal matrix accommodates components of silicates, including olivine. Yellow-green transparent varieties of this mineral are real precious stones. Such a structure and structural features cannot be artificially created. The appearance of the item itself acts as a guarantee of authenticity and uniqueness of the decoration created from a "fallen star" - a meteorite.