![]() ![]() The well-filled risk lists of the space agencies and the recurring reports of close flybys show that it is only a matter of time before the next larger asteroid comes dangerously close to Earth on its orbit through our solar system or even hits it. What are the options for protecting Earth from asteroids? This was due to its comparatively small size and its approach from the direction of the Sun. The Chelyabinsk asteroid nevertheless remained undetected until its impact. This systematic scanning of the sky has led to new asteroids being discovered almost daily today. Since the 1990s, the search for asteroids has been conducted using automated search programmes. This led to a rapid increase in the number of known asteroids. It was not until the advent of photography that it became possible to detect faint objects by using particularly light-sensitive emulsions with long exposure times and tracking the object with the telescope. Due to the relatively low light sensitivity of the human eye, however, this approach only allowed the discovery of very bright asteroids. Until 1890, asteroids could only be found by comparing telescopic observations with existing celestial maps. The 1908 impact could not have been predicted, whereas prediction would have been theoretically possible for the 2013 impact. Could the 19 impacts have been predicted? Experts estimate the diameter of the entire asteroid at about 17 to 20 metres. A little over six months after the impact, a fragment of the asteroid weighing more than 570 kilograms was recovered from Lake Chebarkul, 80 kilometres southwest of Chelyabinsk. This asteroid also broke apart while still in the air, causing a shock wave that damaged numerous buildings around the city of Chelyabinsk in the Russian Urals. In contrast, almost 1,500 people were injured in the impact of the Chelyabinsk asteroid. Despite an explosive force comparable to several megatons of TNT, the damage caused in the sparsely populated area was still comparatively minor. For this reason, it is assumed that the asteroid broke into many small pieces before the impact. However, no impact crater has been found to date. Eyewitnesses could still observe a rising dust fountain in Kirensk, 450 kilometres away. The asteroid exploded about five to fourteen kilometres above the ground, causing a shock wave that uprooted trees over an area of more than 2,000 square kilometres in what is now the Krasnoyarsk region of northern Siberia and smashed windows and doors in the trading settlement of Wanawara, 65 kilometres away. The cause of the Tunguska explosion was most likely the entry of a 30 to 40 metre large asteroid into the Earth's atmosphere. However, events such as the Tunguska explosion on 30 June 1908 and the impact of the Chelyabinsk asteroid on 15 February 2013 show that the danger should not be underestimated. Compared to the increasingly visible consequences of environmental destruction, the extinction of species and climate change, the threat to humanity from asteroid impacts seems literally far away.
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