The film industry regularly hits us with catastrophe films: burning skyscrapers, crashing planes, erupting volcanoes, earthquakes or cosmic catastrophes. In this case the argument is very simple; From space comes an object that threatens life on our planet. If the last one was Moonfall , the first one was a movie from the 50s called When worlds collide , and it narrates the discovery of a planet, Zyra, orbiting around a star, Bellus. The problem is that Zyra is going to pass so close to Earth that it will cause incredible catastrophes. And as if that weren’t enough, 19 days later Bellus will crash into Earth… or what’s left of it. The only salvation is to build a spaceship that, like Noah’s Ark, transports part of humanity to its new home, the very planet Zyra.
What the movie industry has been telling us ever since is something astronomers have known for quite some time: We don’t live in a very quiet neighborhood . Our peaceful cosmic life can be disrupted by the unexpected arrival of an asteroid or a comet whose orbit crosses the Earth’s.
This will happen if an asteroid collides with Earth
His arrival would be preceded by a tremendous explosion in the upper atmosphere. Part of the ozone layer would be destroyed . The asteroid would break up and some of it would vaporize, as would the point on the Earth’s surface just below it. The nitric acid created by the incoming fireball would acidify soils, rivers, lakes, and oceans. If it fell into the sea, immense tsunamis would devastate the coasts of the five continents. If it were to crash into the ground, the impact would create a crater three times the size of the asteroid. The Earth would resound like a bell, triggering seismic and volcanic activity both in the impact zone and in its antipodes. For an hour and a half, the ejected materials would produce a firestorm that would quickly spread across the continent.
The amount of dust and small particles thrown into the atmosphere would make the Earth a place of perpetual night , dropping the temperature by several tens of degrees Celsius. Months later, the low temperatures would force the oceans to release their immense store of carbon dioxide. Together with water vapor, they would cause an increase in the greenhouse effect and the global temperature of the Earth would increase drastically. To put it in two words: global extinction.
For this we only need an asteroid between one and ten kilometers in diameter. In the worst case, the energy of the impact would be about 500,000 times the global nuclear potential. And the probability of an object falling a little over a kilometer in the next 50 years is one in 6,000 or one in 20,000. It really isn’t much: it’s more difficult for you to win the lottery .
Where do the destroyers of worlds come from?
The cosmic sword of Damocles that hangs over our heads is made of ice, metal and rock: they are the asteroids and comets. Comets, relics of when the Solar System was formed, are located in two zones: the Oort cloud and the Kuiper belt . The Oort cloud is a gigantic halo of comets located far beyond the orbit of Pluto, about 60,000 times the distance from Earth to the Sun. When something disturbs their precarious stability, they fall towards the Sun, where they take 500 minutes to reach. millions of years. The Kuiper belt is closer. It is a dense ring of comets, asteroids, and other smaller bodies that extends from the orbit of Neptune to beyond that of Pluto. From there we get the comets that have an orbital period of less than 20 years.
Asteroids are mostly found in a belt between the orbits of Mars and Jupiter. These bodies pose no threat. The problem is the thousands of asteroids with steep orbits that cross the path of the Earth. They are the Near Earth Objects , Near Earth Objects or NEOs.
Dangerous Near Earth Objects
The collective name of NEOs is used for those comets and asteroids that, due to the type of trajectory they follow, are capable of colliding with the Earth . Of the comets, all those that have their closest point to the Sun inside the Earth’s orbit are potentially dangerous. It is difficult to estimate their number , because in addition to those that return from time to time there are those that approach the Sun for the first time. We can calculate how many of the ‘usual’ ones represent a danger. Of the short-period comets that cross the Earth’s orbit, 30 are one kilometer in diameter, 125 are larger than 500 meters and 3,000 larger than 100 meters. We have one consolation: if one were to head towards us, we would most likely see it coming. The ones we would not see arrive are the asteroids .
Of the asteroids whose orbital movement brings them relatively close to Earth, it is estimated that there are about 1,000. The ones we have found range in size from 32 kilometers to less than 100 meters. The reason we don’t know about smaller asteroids is not because they don’t exist but because they are hard to find.
Known NEO asteroids have been classified into different groups: Aten, Amor, Apollo and Arjuna. The most dangerous are those of the Apollo group , since they have their perihelion -the point of the orbit closest to the Sun- inside the Earth’s orbit. Of them we only know 169.
Within the NEOs, the truly dangerous ones are the Earth-Crossing Asteroids . They are NEOs that, due to the gravitational pull of the planets they are approaching, have settled into new orbits too close to feel comfortable. The largest ones we know of are 1627 Ivar and 1580 Betulia , both about 8 kilometers in diameter – about the same size as the meteorite that is supposed to have caused the extinction of the dinosaurs. Knowing how many there are is complicated but we can give some data: it is estimated that there are about 2,000 over a kilometer in diameter; greater than 500 meters, about 10,000; of 100 meters, 300,000 and of 10 meters there can be 150 million. Below that size they are not dangerous: every year one usually reaches us but it disintegrates before reaching the ground. Of these asteroids we have only identified 150 and, to make matters worse, only half of them have we been able to establish their orbit with some precision , so they can be lost -and in fact they are- easily. A couple of good reasons to worry.
References:
Barnes-Svarney, P. (1993) Asteroid. Earth destroyer or new frontier?, Plenum Press
Cox, DW, Chestek, JH (1998) The Doomsday Asteroid, Grupo Editorial Ceac
