An interesting question: how many asteroids fall to earth? If you look at the moon or the planet Mercury with a telescope, you can conclude that asteroids often fall on their surface. They are literally littered with hundreds of craters of varying sizes left over from the fall. On Earth, there are such craters too, but they are much smaller. Does this mean that asteroids almost never fall to earth?
Our earth would be similarly dotted with many craters if there were neither winds nor rain, snow, other weather or geological activity. Movement of tectonic plates, volcanic eruptions, mining processes. For thousands of years, and especially for millions of years, they can not only "hide" a crater of any size, but also wipe out entire mountain ranges in the sand. Do not forget the sedimentary rocks – many impact craters are simply buried under layers of organic sediments in the multimeter range. But all the above features are unable to hide the biggest "scars" on the surface of the planet from the fall of the largest asteroids and meteorites.
Arizona crater. One of the largest meteorite craters in the world: diameter 1219 meters, depth 229 meters
Asteroid, meteoroid, meteor and meteorite – what's the difference?
A little theory. Asteroids are small celestial bodies that have remained in our solar system since their formation about 4.5 billion years ago. As a rule, objects with a diameter of more than 1 meter are defined as such. In the solar system there are several places with a high concentration of asteroids. These places are called asteroid belts. One of them – the "main belt" – is located between Mars and Jupiter, the second – beyond Neptune's orbit.
Some asteroids can fly past our planet. If such asteroids approach our planet at a distance of 50 million kilometers, we speak of near-natural nature. Potentially dangerous objects are objects over 140 meters in size that can approach our planet at a distance of 7.5 million kilometers or less.
Objects less than 1 meter in diameter are called meteorites. The smallest of them can weigh less than 1 gram. When a meteorite collides with the planet's atmosphere, it begins to experience strong friction against the particles of the atmosphere and burns quickly, leaving a bright trail of fire in the sky. This path is called Meteor. When one and the same meteorite reaches the surface of the planet or the entire planet or is split into many parts, 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 located in the so-called asteroid belts (beyond the orbit of Mars, Jupiter and Neptune), but these regions are well studied. The problem is that we know almost nothing about more remote areas of space in our solar system. And do not imagine that there could be hiding places.
Asteroids are hard to spot for several reasons. The most important are: size, shape, distance to earth, their albedo (how much light they reflect) and speed. At a distance of several million kilometers, try to detect a small flat object several meters in size that moves at a speed of 36,000 kilometers per hour.
Fortunately, technologies are evolving, and astronomers can predict the fall of the smallest objects (several meters in size) on Earth in just a day or two before they enter the planet's atmosphere. And even determine the likely place of the fall. The approximation of larger objects can predict scientists for many years.
See also: Help astronomers find new asteroids in the Hubble images
The smallest objects are usually not a real threat. Flown into our atmosphere, they just burn in it. Where there is a greater risk, objects with a size of 100 meters and more can be. It is these asteroids that can cause the greatest destruction on Earth, much like the effects of nuclear bombardment.
See also: Named the most dangerous asteroids. One of them could fall to earth in September 2019
How many asteroids are near the earth?
Nobody can tell you exact data, but according to a number of specialists, there can be up to half a billion asteroids one meter or more in near-Earth orbit. Every year, scientists estimate the likelihood of overthrowing the largest of them on Earth.
Schematic representation of near-earth objects around our planet (yellow dot in the middle)
Estimating the likelihood of an asteroid falling to Earth is made by a complex computer simulation. After discovering a new object, the scientists write it down in a catalog and then use computer simulations to calculate many factors: the current orbit of the asteroid, its size, current position and distance to Earth, etc. It is predicted that the asteroid and the earth will cut at one time or another. As mentioned earlier, most scientists try to predict the likelihood that only objects that can pose a real threat will fall.
How often do asteroids fall to earth?
According to statistics, something falls daily from space to earth. According to Bruce Betts of the Planetary Society, about 100 tons of different space objects enter the Earth's atmosphere every day. However, most of these objects have a size of grains of sand up to 1 meter. They certainly do not reach the ground as they burn in the atmosphere.
Each year, about 30 small asteroids speak each year, measuring several meters in the atmosphere of the planet. Sometimes fragments of these objects fall to earth in the form of meteorites.
Larger, only 20 meters tall and exploding over Chelyabinsk in 2013, come to earth once or twice on average in 100 years. They are not a global problem, but if such an asteroid falls somewhere in a densely populated region, the consequences can not be described as pleasant.
Trail from the Chelyabinsk meteorite in the atmosphere. Photos from 2013
Objects similar to those that exploded 111 years ago in the atmosphere of the Podkamennaya Tunguska River fall to Earth once or twice a thousand years. According to the latest scientists, its dimensions were 75 meters.
When we talk about several hundred meters of asteroids, they only fall once every few hundred thousand years. The largest asteroids – from a distance of ten kilometers or more (one of them, we remember, has led to the extinction of dinosaurs, and generally 70 percent of the total life on Earth some 65 million years ago), can not, scientists say fall once in 100 million years.
Of course, the fall of such giants on Earth will mean the end of our entire civilization. Smaller asteroids can cause severe local destruction in the same country. However, one can only guess at the actual consequences of such destruction if an even small asteroid falls somewhere in a densely populated industrial region.
What is the probability of dying from an asteroid?
If we start from the top, we can conclude that the larger the asteroid, the lower the likelihood of the asteroid falling to Earth. The asteroid threat is undoubtedly real. But the concrete chances of perishing on an asteroid are much less than the probability of perishing on the same lightning. And it's 1 to 280 000. At least according to American experts. By the way, you can win the same roulette with a probability of 1 to 37.
Russian experts give slightly less optimistic forecasts. For example, according to the Director-General of the Center for Planetary Protection Anatoly Zaitsev, the likelihood of an asteroid crashing on Earth equals the likelihood of a plane crash. At the same time, he notes that more than a hundred asteroids of different sizes fly past the earth at safe distances.
How can you reflect the asteroid threat?
Scientists around the world are not only observing asteroids, but also trying to develop effective methods to ward off real asteroid threats. Possible means include, for example, the use of nuclear weapons, the ramming of large asteroids with multiple spacecraft, the capture of asteroids and their retreat from the dangerous trajectory of approach to Earth.
See also: Scientists suggest shooting down dangerous asteroids with nuclear charges