It can seem that death due to the impact of a meteorite on the Earth is a very unlikely phenomenon. Nevertheless, it is estimated that every year the are some persons who die from meteorite impacts. They are rocks of different sizes, travelling at thousands of kilometres per hour, and if one of these, by small it might be, impacts a person, it can be lethal.
Different sizes and different risks
Small meteorite
The solar system is full of billions of celestial bodies, all of them following varied trajectories, as the famous Newton laws indicate, for which it is very probable for one of these bodies to impact the Earth. However, the majority of these bodies are very small, in the order of a gram or less, as the micro-meteorites, which don’t represent any danger to the human species. In fact, these micro-meteorites provoke a beautiful phenomenon: the named shooting stars, which we can observe during the night.
Big rocks
As we have seen, the micro-meteorites are inoffensive and they even offer us a great spectacle, but the bigger meteorites, of tens and hundreds of meters in diameter, or even kilometres, represent a big problem. These could impact the Earth, and, in fact, they have done it many times throughout the existence of the Earth.
These big rocks release an enormous quantity of energy when they impact the Earth:
- A meteorite of 25 metres in diameter would release the energy of 1 megaton.
- One of 50 metres would release an energy equivalent to about 10 megatons.
- A rock of 140 metres would release the energy of 300 megatons.
- A meteorite of 300 metres in diameter would release the energy of 2 000 megatons when impacting the Earth.
- One of 600 metres of diameter would produce the energy of 20 000 megatons.
- An impact of a meteorite of one kilometre would release the energy of 100 000 megatons.
- One of 5 kilometres of diameter would provoke an explosion of 10 million megatons.
- A meteorite of 10 kilometres in diameter would release the energy of 100 million megatons when impacting the Earth.
It is calculated that the impact of a meteorite of one kilometre in diameter against the Earth could cause the extinction of the human species on the planet. Currently, it is considered that the massive extinction of the dinosaurs millions of years ago was due to the impact of an object of about 10 kilometres in diameter and the environmental changes that followed the collision. This meteorite created a crater of 150 metres in diameter on the Yucatan Peninsula.
But we don’t have to go so far in the past to find other important meteorite impacts. In 1908 a meteorite of 50 metres in diameter fell on the Russian region of Tunguska. It didn’t even manage to impact against the ground. It volatilised in the air at an altitude of 8 kilometres above the surface, releasing, however, the energy of between 10 and 15 megatons, 1 00 times more than the Hiroshima bomb.
It destroyed 2 000 square kilometres of forests and provoked a shock wave of 5 on the Richter scale. Fortunately, it took place in an uninhabited Siberian zone. The explosion was heard at a distance as big as Spain’s width, and the shock wave gave 3 turns around the planet and generated winds, fires, and the disappearance of part of the ozone in the atmosphere. And all this was provoked by a rock of only 50 metres, the size of a house, that didn’t even impact the ground.
Good news
The Tunguska event was due to a rock of only 50 metres, and through space, there are thousands of other asteroids with much bigger sizes, of hundreds of metres or even kilometres. However, there is some “good news” that shows us that the impact risk isn’t too big (even if the impact possibility exists and many collisions against asteroids will take place):
- In the solar system, there are billions of celestial bodies that can impact the Earth. Nevertheless, it is also true that the big majority of them have a very small size. Their distribution follows an exponential law: there are many very small meteoroids, and the abundance declines rapidly when their size increases. The small ones are the ones that give rise to phenomena such as the shooting stars, nice and harmless, whereas the big meteorites are the ones that can cause enormous destruction on the Earth. The asteroids of big size aren’t very abundant.
- The Earth is a very small part of the solar system. Due to the enormous space that separates the planets and the different celestial bodies that form part of it, we could say that the solar system is empty. In fact, if we put the solar system at scale, we realise the enormous distances that form it. If we represent the Sun as a sphere of one metre of diameter, the Earth would be situated at a distance of 1087,5 metres and would be represented by a sphere of 9 millimetres. In conclusion, it is very difficult for one of the asteroids of the solar system to impact the Earth.
- But in the case that it fell on the Earth, if it was of reduced size, it wouldn’t be so important either. Once again, we occupy a very small surface. The surface of a human being is about 300 cm2, while the surface of the Earth is about 510 million square kilometres. So, the possibility for a meteorite to fall where a person is, is, more or less, of one between 1016. Moreover, the human species only occupies 3% of the total surface of the Earth. The most probable place for a meteorite to fall is, for example, into the ocean, in the deserts or in the big uninhabited spaces.
- The possibility for a human being to die from the impact of a meteorite is extremely low. There are so few possibilities that a small meteorite impacted a person, like the one that a big asteroid impacted the Earth. But still, we are talking of low possibilities, but not absent. A small meteorite has to impact well to hurt, but this is not the case with a big one. As we have seen, an asteroid of one kilometre doesn’t need to aim much to cause an authentic disaster on the Earth. Even if it is unlikely, in the long term it seems inevitable that a large asteroid could hit the Earth. We don’t know when, but yes (more or less) every when it takes place:
| Size of the meteorite | Years every when it falls |
| 25 metres | 200 years |
| 50 metres | 2 000 years |
| 140 metres | 30 000 years |
| 300 metres | 100 000 years |
| 600 metres | 200 000 years |
| 1 kilometre | 700 000 years |
| 5 kilometre | 30 000 000 years |
| 10 kilometre | 100 000 000 years |
As we see, these numbers are enormous, which also makes us realise that our existence is very short. So, we are small in the space but we are also very small in time. It is very unlikely that in our lifetime we lived a situation like this.
- But, if this took place, couldn’t we do something about it? Thanks to Newton’s laws we can know where Mars will be in 200 or 1 000 years, as we can also know where an asteroid will be in some time and compare it with the Earth’s position at that moment. The problem is that asteroids are relatively small don’t emit light and are dark. In conclusion, we cannot see them, so they are very difficult to find. To this, it is also added the possibility that, due to planetary disturbances, its orbit could be affected. With Newton’s equations, we can know the interactions between two bodies, but when other bodies are added, the equations don’t work. But, however, many projects arise to find dangerous asteroids and observe their orbits.
- In any case, if we found a meteorite that could impact the Earth we could find different solutions to the problem. What is seen in some science-fiction films in which an asteroid is destroyed wouldn’t be a good option. If we break an asteroid into many parts, what is accomplished is that, instead of falling an only big rock, it makes many relatively small rocks, spread out in a much bigger area, to fall. In addition, it is also possible that the own gravity of the different rocks would rejoin to form the initial asteroid. Therefore, this one doesn’t seem like a good solution.
The most intelligent solution isn’t even to deviate it. What would have to be done, whereas, would be to change its speed: slowing it down, or speeding up the asteroid. If we achieve the asteroid to go more quickly, we will get it to pass throughout the orbit of the Earth before our planet arrived there. If we slow it down, the Earth will arrive at the point where the asteroid has to pass before this one does it.
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