Interest Ask: how many asteroids fall on Earth? If you look at the moon or the planet Mercury with a telescope, you can conclude that asteroids fall on their surface quite often. They are literally littered with hundreds of craters of various sizes left over from the fall. On Earth, such craters can also be found, but they are much smaller. Does this mean that asteroids almost never fall to Earth?
Our Earth would be littered with manycraters, if there were no winds, rains, snow, other weather processes, as well as geological activity. Movement of tectonic plates, volcanic eruptions, mountain building processes. For millennia, and even more so for millions of years, they can not only “hide” a crater of any size, but also erase whole mountain ranges in the sand. Do not forget about sedimentary rocks - many impact craters are simply buried under multimeter layers of organic sediments. But all the above features are not able to hide the biggest "scars" left on the surface of the planet from the fall of the largest asteroids and meteorites.
Arizona crater. One of the largest meteorite craters on Earth: diameter 1219 meters, depth 229 meters
Asteroid, meteoroid, meteor and meteorite - what's the difference?
A bit of theory. Asteroids are small celestial bodies that remained in our solar system after its formation about 4.5 billion years ago. Usually such a definition is given to objects whose dimensions are greater than 1 meter in diameter. In the solar system there are several places with large concentrations of asteroids. These places are called asteroid belts. One of them - the "main belt" - is located between Mars and Jupiter, the second - beyond the orbit of Neptune.
Some asteroids can fly past ourthe planets. If such asteroids are approaching our planet at a distance of 50 million kilometers, they are called near-earth. Potentially dangerous objects are objects with a size of more than 140 meters, which can approach our planet at a distance of 7.5 million kilometers or less.
Objects less than 1 meter in diameter takencall meteorods. The smallest of them can weigh less than 1 gram. When a meteoroid collides with the atmosphere of the planet, it begins to experience strong friction against the particles of the atmosphere and quickly burns, leaving behind a bright trail of fire in the sky. This trail is called a meteor. Moreover, if all the same meteoroid reaches the surface of the planet or as a whole, or split into many parts, then it is called a meteorite. In fact, an asteroid can also become a meteorite.
Why is the search for asteroids so difficult?
Most known asteroids are incalled asteroid belts (beyond the orbits of Mars, Jupiter and Neptune), but these regions are fairly well studied. The problem is that we know almost nothing about more remote areas of the space of our solar system. And do not imagine that there may be hiding.
Asteroids are difficult to detect for a number of reasons. The main ones are: size, shape, distance to the Earth, their albedo (how much light they reflect) and speed. Try to detect at a distance of several million kilometers a small flat object measuring several meters in size, moving at a speed of 36,000 kilometers per hour.
Fortunately, technology is evolving, and astronomersthey can already predict the fall of the smallest objects (several meters in size) to Earth in about a day or two before they enter the planet’s atmosphere. And even determine the likely place of the fall. Approximation of larger objects, scientists can predict for many years.
See also: Help astronomers to find new asteroids in the Hubble images
The smallest objects are usually notpose a real threat. Having flown to our atmosphere, they simply burn in it. Where a greater danger can be objects of size from 100 meters and more. It is these asteroids that can cause the greatest destruction on Earth, similar to the effects of nuclear bombardment.
See also: Named the most dangerous asteroids. One of them may fall to Earth in September 2019
How many asteroids are near Earth?
No one can tell exact data, but according toa number of specialists, in Earth orbit can be up to half a billion asteroids with a size of one meter or more. Every year, scientists assess the likelihood of the fall of the largest of them Earth.
Schematic representation of near-Earth objects around our planet (yellow dot in the center)
Estimation of the probability of an asteroid falling to Earthcarried out using sophisticated computer simulation. Having discovered a new object, scientists write it in a catalog, and then use computer simulations, in which many factors are calculated: the current orbit of the asteroid, its size, current location and distance relative to the Earth, and so on. From this it is predicted that the asteroid and the Earth will intersect at one or another point in time. As noted above, mostly scientists are trying to predict the chances of falling only those objects that can carry a real threat.
How often do asteroids fall on Earth?
According to statistics, to Earth from spaceevery day something falls. According to Bruce Betts from Planetary Society, about 100 tons of various space objects penetrate the Earth’s atmosphere daily, but most of these objects range in size from grains of sand to 1 meter. They certainly do not reach the ground, as they burn in the atmosphere.
His speak in an annualized ratio, then every year about 30 small asteroids measuring several meters into the atmosphere of the planet. Sometimes fragments of these objects fall to the earth in the form of meteorites.
Larger, ranging in size from 20 meters, as one ofthose that exploded over Chelyabinsk in 2013, on average, fly to Earth once or twice in 100 years. They are not a global problem, but if such an asteroid falls somewhere in a densely populated region, then the consequences cannot be called pleasant.
Trail from the Chelyabinsk meteorite in the atmosphere. Photos of 2013
Objects similar to the one that exploded 111 yearsback in the atmosphere near the Podkamennaya Tunguska River, they fall to the Earth once or twice a thousand years. According to the latest data of scientists, its dimensions were 75 meters.
If we talk about larger asteroids,several hundred meters in size, they fall no more than once every several hundred thousand years. The largest asteroids - from 10 kilometers and more (one of them, we recall, led to the extinction of dinosaurs and generally 70 percent of all life on Earth about 65 million years), according to scientists, can fall no more than once in 100 million years.
Of course, the fall of such giants to the Earth will besignify the end of our entire civilization. Smaller asteroids can cause severe local destruction within the same country. But one can only guess about the real consequences of such destruction if an asteroid of even a small size falls somewhere in a densely populated industrial region.
What is the probability to die from an asteroid?
If we proceed from the above, we can dothe conclusion is that the larger the asteroid, the less chance it will fall to Earth. The asteroid threat is certainly real. But the concrete chances of perishing from an asteroid are much less than the probability of perishing from the same lightning. And it is 1 to 280 000. At least, according to American experts. By the way, you can win the same roulette with about 1 to 37 probability.
Russian experts give a little less optimisticforecasts. For example, according to the Director General of the Center for Planetary Protection Anatoly Zaitsev, the likelihood of the fall of an asteroid on Earth equals the probability of a plane crash. At the same time, he notes that more than a hundred asteroids of various sizes fly by at Earth at safe distances past the Earth.
How to reflect the asteroid threat?
Scientists around the world are not only watchingasteroids, but also trying to develop effective methods to repel real asteroid threats. For example, among the possible means are: the use of nuclear weapons, the ram of large asteroids with multi-ton spacecraft, the catching of asteroids and their withdrawal from the dangerous trajectory of approach to the Earth.
See also: Scientists propose to shoot down dangerous asteroids with nuclear charges