On July 25, the asteroid 2019 OK , about 75 meters in diameter, passed just 71,000 km from our planet , a fifth of the distance to the Moon. Worse was on February 9, 2013 , when the 30 meter diameter asteroid 367943 Duende , discovered in 2012 by Majorcan astronomers from the La Sagra Observatory (Granada), passed the record distance of 27,000 km from the Earth’s surface, for below the orbit of our telecommunications satellites , which are located around 35,000 km high.
2019 OK is one of those asteroids called City Destroyers, or CityKillers, and this last-minute detection reveals that we still have a lot to learn about the immediate space around us. “This is not a Hollywood movie,” adds Duffy. “We are facing a very real and close danger.” Proof of this we had on the morning of February 15, 2013 , when a meteorite of about 20 meters and weighing 10,000 tons crossed the sky south of the Urals and above the Russian city of Chelyabinsk to end up exploding 80 km from distance and 20 high: the shock wave raised roofs and broke windows, leaving more than a thousand injured and 30 million euros in repairs.
The terrifying thing is that not even a century had passed since something similar happened on the other side of the Urals, some 1,600 km east of Moscow. In the valley of the Tunguska River. At 7 am on June 30, 1908, a fireball with a diameter larger than a football field and loaded with 10 million tons of stones exploded at a height of 8 kilometers . In an instant trees and reindeer were annihilated in a radius of 50 km. The blast wave engulfed the Earth , throwing so much dust into the stratosphere that sunlight was scattered from the lighted side of the globe to the dark side. And 10,000 km away, in London, the midnight sky lit up like sunset. Life disappeared in an area of 2,000 square kilometers .
The Tunguska event shows us that this poetic image of an isolated Earth, a lonely blue rock sailing through space, is totally wrong. In our journey around the Sun (a path of 900 million kilometers covered in 30 million seconds) we are accompanied by eight planets, innumerable moons, asteroids and comets, interplanetary dust, cosmic radiation, neutrinos, solar wind… Every second we advance 30 kilometers through space and if there is something ahead waiting for us or heading to the same place as us, we will find it. And it is not something strange: every year between 35 and 100,000 tons of interplanetary material reach the atmosphere . Fortunately, most of these fragments are so small that they burn up on contact with the atmosphere , leaving trails that we know as shooting stars. But some others are a bit bigger; those the size of a fist reach Earth every two hours, according to a study by the international team that makes up the Meteorite Observation and Recovery Program.
What happens when a fireball from outer space crosses our planet? It all starts with the appearance of a fireball in the sky, which is the compressed air in front of the rock that is heated by the effect of friction with the atmosphere and whose size can be larger than that of the rock itself. Meanwhile, the surface of it melts, forming large flashes in the tail and trails of smoke that can continue to be seen in the sky even after the fall. The rock can end up disintegrating before reaching the ground and a shower of stones end up hitting the ground at a speed of 2,000 meters per second, similar to that of a jet diving. And all this accompanied by the thunderous roar of the shock wave that reverberates, according to a witness, “like the sound of cannons in battle.” If the explosion happens at high altitude , we can prepare for a torrential rain of stones, like the one in Poland in 1868: 100,000 stones fell , most of them smaller than pieces of shrapnel. And there are other types of meteorites, which are essentially pieces of iron, which can withstand the impact of the atmosphere without breaking and reach the ground intact.
Space fireballs reach the Earth’s atmosphere at speeds of up to 80 km/s and the damage they can do depends on their kinetic energy . Thus, two objects moving at the same speed possess an energy that is proportional to their mass. The damage also depends on how fast they move. Doubling the speed quadruples the energy, so a tenth-of-a-gram grain of dust at 80 kilometers per second has as much energy as a one-tonne car at 80 kilometers per hour. In this way, an interplanetary particle weighing one gram reaches the atmosphere with a shock power similar to that of a high-speed truck. And the worst can reach speeds of Mach 50: these are the ones that disappear underground leaving a deep crater.
Let us imagine that a 5 km destroyer of worlds is coming towards us on a collision course. It could collide with us from the front or from behind, which means a collision at a speed between 15 and 80 km/s. If we take 50 km/s as an average, the impact would release in one second an amount of energy similar to all the world’s nuclear sandboxes exploding simultaneously, or half a million intensity 9 earthquakes (the largest ever recorded) at the same time. To get an idea of what that means: the energy released would be capable of ripping the Earth’s atmosphere, and if all that energy were dissipated as heat, the temperature of the air would rise by 190 degrees Celsius . Marine animals far from the impact site would survive as the oceans as a whole would only warm a few degrees, but closed seas like the Mediterranean could boil. And a blanket of thousands of tons of dust would cover the atmosphere for years.
How likely is it that a doomsday asteroid similar to the one that wiped out the dinosaurs will hit us? It’s a difficult calculation because it depends on many unknown variables, but it is estimated that during a human’s lifetime there is roughly a one in 10,000 chance that the Earth will be impacted by something big enough to send survivors back to the Stone Age. .
And it is that the Solar System is a hostile place, and there is no place to hide.