The average time taken by an asteroid to complete its orbit is about five years. However, some have elongated orbits which bring them close to the Sun and the Earth. These minor planets are called "Apollo objects", from the name of the first body that was observed to cross the orbit of our planet, in 1932. We have identified about thirty of such objects, some of which have been "christined" by their discoverer: like Hermes, which in 1937 got as close as 770 000 kilometers (half the distance between the Earth and the Moon) or Eros which, rolling like a rugby ball, passed no less than 23 000 000 kilometers from our planet, or Adonis, Icarus, Dedalus, Midas and Ra-Shalom. But there are probably around 500 to 1 000, according to an estimate that considers the smallest dimensions for which they can be identified with Earth instruments and which help to "rediscover" an object that had already been catalogu1\ed and then literally lost from sight for decades. One of these is Adonis which, identified in 1936, completely "disappeared" for about forty years, during which it crossed the Earth's orbit "in incognito" no less than 30 times. The origin of the minor planets, which have provided a wealth of information to better understand the solar system and its evolution, is still being debated: are these asteroids "off their course" or dead nuclei of ancient comets which have lost their volatile components? Regardless of the answer, astronomers don't feel very secure about these space missiles. As proven by the catastrophic event that occurred 25 000 to 50 000 years ago in North America. Let's go back in time and try to discover what happened in that remote era (though not very remote in geological terms). The place is a plain at the edge of Devil's Canyon in Arizona. Man has not yet reached this location and the animals which inhabit the region live their lives according to the rhythm of nature: the mammoths compete with the antilopes for pasture land and the great saber-tooth tigers can find prey easily wherever they hunt. Suddenly, a bright point appears in the sky. At first it is very small, but soon gets bigger and brighter. It approaches very quickly and silently, and soon even blocks out the Sun. All the animals raise their eyes in alarm, towards that unknown threat that hangs in the sky. But by now it is too late to escape: with a sudden roar the earth seems to explode. An enormous shock wave knocks down trees in a radius of dozens of kilometers in all directions and millions of tons of rock are projected into the air: these enormous masses travel like bullets, but there are also very fine particles which even reach the stratosphere, obscuring the sunlight. When the thick veil of dust is dissipated by the wind and the rain, we are presented with a scene of desolation. Where life once teemed, there is only ravaged ground and carbonized vegetation. And, in the center, an enormous crater with a diameter of more than a kilometer and a depth of about 200 meters, destined to become one of the most famous crater in the world.
The average time taken by an asteroid to complete its orbit is about five years. However, some have elongated orbits which bring them close to the Sun and the Earth. These minor planets are called "Apollo objects", from the name of the first body that was observed to cross the orbit of our planet, in 1932. We have identified about thirty of such objects, some of which have been "christined" by their discoverer: like Hermes, which in 1937 got as close as 770 000 kilometers (half the distance between the Earth and the Moon) or Eros which, rolling like a rugby ball, passed no less than 23 000 000 kilometers from our planet, or Adonis, Icarus, Dedalus, Midas and Ra-Shalom. But there are probably around 500 to 1 000, according to an estimate that considers the smallest dimensions for which they can be identified with Earth instruments and which help to "rediscover" an object that had already been catalogu1\ed and then literally lost from sight for decades. One of these is Adonis which, identified in 1936, completely "disappeared" for about forty years, during which it crossed the Earth's orbit "in incognito" no less than 30 times. The origin of the minor planets, which have provided a wealth of information to better understand the solar system and its evolution, is still being debated: are these asteroids "off their course" or dead nuclei of ancient comets which have lost their volatile components? Regardless of the answer, astronomers don't feel very secure about these space missiles. As proven by the catastrophic event that occurred 25 000 to 50 000 years ago in North America. Let's go back in time and try to discover what happened in that remote era (though not very remote in geological terms). The place is a plain at the edge of Devil's Canyon in Arizona. Man has not yet reached this location and the animals which inhabit the region live their lives according to the rhythm of nature: the mammoths compete with the antilopes for pasture land and the great saber-tooth tigers can find prey easily wherever they hunt. Suddenly, a bright point appears in the sky. At first it is very small, but soon gets bigger and brighter. It approaches very quickly and silently, and soon even blocks out the Sun. All the animals raise their eyes in alarm, towards that unknown threat that hangs in the sky. But by now it is too late to escape: with a sudden roar the earth seems to explode. An enormous shock wave knocks down trees in a radius of dozens of kilometers in all directions and millions of tons of rock are projected into the air: these enormous masses travel like bullets, but there are also very fine particles which even reach the stratosphere, obscuring the sunlight. When the thick veil of dust is dissipated by the wind and the rain, we are presented with a scene of desolation. Where life once teemed, there is only ravaged ground and carbonized vegetation. And, in the center, an enormous crater with a diameter of more than a kilometer and a depth of about 200 meters, destined to become one of the most famous crater in the world.
