This month, a relatively small asteroid flew near the Earth, which was discovered literally six days before. It sounds scary, but the fact is that the possible collision of such an object with the Earth is an extremely unlikely event. Every year more than 50,000 tons of extraterrestrial material (rocks and dust) hit our planet. It all comes down in tiny pieces - even if it all fell at the same time, it would be little more than a truck-sized asteroid that passed by in January.
But while scientists can easily spot fairly large asteroids more than a kilometer across, what risk could smaller asteroids pose that would be more difficult to track? Should we be worried?
It is widely believed that the dinosaurs were destroyed 65 million years ago by the fall of a large asteroid. The ensuing environmental changes - rapid increases in atmospheric temperature, wildfires around the world, then a sharp drop in temperature and acidification of ocean waters - were a consequence of the size of the asteroid. Most likely, it was about 10 kilometers across.
It is almost three times larger in diameter and about 30 million times heavier than the entire annual supply of asteroids striking us today.
Five years ago, the Earth had an encounter with an object 20 meters across that exploded over Chelyabinsk in Russia. No one noticed his approach. Stunning footage of the fireball was recorded on video recorders of people driving to work in the morning. They were shocked to see how a rocket or a meteor lit up the dark February morning.
The rock exploded in the atmosphere, and many fragments of the meteorite scattered across the territory. The largest piece, weighing 600 kilograms, was found a few months later in a lake covered with ice. Although many people were injured, most of the injuries were attributed to broken glass from the atmospheric shockwave.
Residents of the Chelyabinsk region were lucky - the asteroid collapsed 30 kilometers above the surface and did not leave a crater. Fortunately, this is most often the case.
A collision crater is formed only if the asteroid is more than 50 meters across. And even if it is 2-3 kilometers wide, this will not be enough to cause a global extinction. Of course, serious problems will arise at the impact site, especially if it falls on a populated area.
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Threat monitoring
There are several international observational programs that use robotic telescopes specifically designed to map all near-Earth objects (NEO). Among them are asteroids approaching the Sun closer than 1.3 AU. e. - 1 a. e. = distance from the Earth to the Sun. Special attention is paid to "potentially dangerous objects", near-Earth objects 150 meters in diameter, whose orbits cross the Earth's orbit.
Fortunately, almost all of these objects are located in stable orbits and are not dangerous. Today we can observe asteroids even five meters in diameter. But as the event in Chelyabinsk showed, these objects still manage to slip past the observers. Part of the reason that the Chelyabinsk object went undetected is that it entered the atmosphere at a very low angle from the direction of the sun. But the main reason is that there are many such objects, and we have been observing them not so long ago (about ten years).
Minot Planet Center maintains an observational database of 17,500 objects at the end of December 2017. Another 28 objects were discovered this month. Our planet is surrounded by a swarm of possible intruders, but we keep them at a distance.
One of the main problems of our civilization is that although we are increasingly effective in detecting NEO, there is nothing we can do to prevent it from colliding with the Earth. NASA is currently developing the Double Asteroid Redirection Test (DART) project to redirect threatening asteroids in time. A spacecraft 1.5 meters long will be able to crash into an asteroid like Didymos B. Didymos B orbits Dydimos A. The goal of the project is to change the orbit of Dydimos B around its partner, without changing the orbit of Dydimos A around the sun.
DART will launch in December 2020 and meet with the asteroid in October 2022. There are less than five years left before we know if we can defend our planet from a real threat.
Today, although small asteroids can be dangerous, this threat is local and less dangerous than that carried by large asteroids. Therefore, it is not yet necessary to collect matches and salt in case of an asteroid attack. The 50,000 tons of cosmic material that hits Earth each year is mostly precipitated as dust particles less than a millimeter in diameter. They do not pose a threat to humanity.
Ilya Khel
