Whilst the blog has been off-line, the event that really grabbed my attention since my last entry occurred at 3.20 UTC on 15thFebruary 2013 with the entry into the atmosphere of a meteorite over Russia. This object was estimated to be around 17 m in diameter, which is illustrated in comparison with a jumbo jet in the accompanying picture. This may not look very large, but an object of this size made of dense rocky and metallic material was estimated to have had a mass of around 11,000 tonnes. Combine this with the fact that its entry speed was of the order of 18 km/sec and you have an awful lot of energy. For those with a scientific background this is around 2 ×10 to the power of 15 J. This is the sort of energy released by very significant nuclear weapons, equivalent to about half a megaton of the high explosive TNT (which is about 35 Hiroshima bombs in magnitude).
The accompanying video is one of the many showing the flight from atmospheric entry at around 70 – 80 km altitude down to the bright flash of the airburst that was estimated to occur at around 25 km altitude. Not all the energy of entry was released in the airburst, when the object finally broke-up, but much was absorbed by the atmosphere, and released in the shockwave and the intense flash of light and thermal emission. The consequence for those on the ground in the neighbourhood of the city of Chelyabinsk was around 1500 casualties, mostly as a result of broken glass caused by the impacting shockwave.
This is the largest known object to enter the Earth’s atmosphere since the Tunguska event in 1908. This resulted in an airburst over an unpopulated region of Siberia with a larger energy than the Chelyabinsk meteorite. Fortunately the 1908 event occurred in an unpopulated region, and resulted in the devastation of an area of forestation of about 2000 square kilometres.
Hopefully the full analysis of the Chelyabinsk event will help us to appreciate and understand better the consequences of the impact of near-Earth objects (NEOs), and encourage us to invest in efforts to detect and catalogue such objects in orbit around the Sun. Also the technology to divert the paths of such objects from an impact trajectory is available now. But these technologies need to be tested and calibrated now, and not later when they may need to be applied ‘in anger’. Current theories suggest that the reign of the dinosaurs was brought to an end by the impact of a large NEO. The question is – can we demonstrate that we are indeed clever-er than the dinosaurs before our species is presented with an extinction-level threat posed by the NEO population?
The accompanying video is one of the many showing the flight from atmospheric entry at around 70 – 80 km altitude down to the bright flash of the airburst that was estimated to occur at around 25 km altitude. Not all the energy of entry was released in the airburst, when the object finally broke-up, but much was absorbed by the atmosphere, and released in the shockwave and the intense flash of light and thermal emission. The consequence for those on the ground in the neighbourhood of the city of Chelyabinsk was around 1500 casualties, mostly as a result of broken glass caused by the impacting shockwave.
This is the largest known object to enter the Earth’s atmosphere since the Tunguska event in 1908. This resulted in an airburst over an unpopulated region of Siberia with a larger energy than the Chelyabinsk meteorite. Fortunately the 1908 event occurred in an unpopulated region, and resulted in the devastation of an area of forestation of about 2000 square kilometres.
Hopefully the full analysis of the Chelyabinsk event will help us to appreciate and understand better the consequences of the impact of near-Earth objects (NEOs), and encourage us to invest in efforts to detect and catalogue such objects in orbit around the Sun. Also the technology to divert the paths of such objects from an impact trajectory is available now. But these technologies need to be tested and calibrated now, and not later when they may need to be applied ‘in anger’. Current theories suggest that the reign of the dinosaurs was brought to an end by the impact of a large NEO. The question is – can we demonstrate that we are indeed clever-er than the dinosaurs before our species is presented with an extinction-level threat posed by the NEO population?
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