In the Solar System, there is strong evidence that asteroids hit our and other planets from time to time. According to the Lunar and Planetary Laboratory at the University of Arizona in the history of the Earth there have been more than 3 million impact craters larger than 1 km in diameter produced from impacting objects, the largest craters stretching more than 1000 km in diameter!!
Today, due to many geological processes on Earth there are about 160 surviving impact craters found on Earth so far. These are shown in the picture below.
Earth is not the only place where this phenomenon takes place. In fact, all solid bodies such as the rocky planets, their moons and asteroids are covered with craters ranging from a few meters to huge structures.
The first crater ever recognized on Earth as being generated by a NEO impact was Arizona’s mile-wide Meteor Crater, also called Barringer Crater. A second famous impact site, located off the coast of the Yucatan Peninsula in Mexico, is the Chicxulub crater, buried under ocean sediments and believed to be a record of the event that led to the extinction of the dinosaurs 65 million years ago. Fortunately for us, these big asteroid impacts are extremely rare.
But how dangerous can an impact be?
The answer to this question depends on the impactor’s characteristics. Firstly, on the kinetic energy of the colliding body, so the object mass and orbit are key parameters in assessing the risk to Earth. Most of the objects that fall on Earth are not bigger than a meter and are therefore destroyed before they reach the ground. In fact, on our planet about 100 tons of interplanetary material rift down to Earth daily. Luckily, most of these objects are too small to reach the ground, and don’t represent a danger, since our atmosphere acts as a real shield, burning out all small debris. Burning up, the debris can leave beautiful trails of light known as meteors or “shooting stars”.
The possibility of fragmentation or explosion of the asteroid before reaching the ground, and the consequences of an impact can be dramatically different depending on the object’s internal structure and composition. Therefore, good knowledge about the physical properties of a NEO is necessary to calculate not just its impact energy but also the emerging consequences of a collision with our planet.
For our heavily populated world and highly networked society the impact of an asteroid or comet on the Earth today could produce a natural catastrophe far more damaging to civilization than any in recorded history.
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