Asteroid 2012 DA14 is making an exceptionally close pass by the Earth on Friday. In fact, it will be passing closer than any other asteroid of its size that we know of!
Astronomers know its orbit so well now that they say there is absolutely no chance of it hitting us, but what would happen if if did?
There are plenty of computer simulations around that can estimate the impact of such an object (Impact Earth is a really good one), but there has actually been a real-world example of such an event that we can look at as an example.
Just past midnight, Greenwich Mean Time, on June 30th, 1908 an object plowed into our atmosphere going roughly 40,000 km/h, and exploded about 5-10 kilometres above central Russia. The explosion generated an air blast equivalent to a 10-15 megaton nuclear bomb, flattening an estimated 80 million trees across over 2,000 square kilometres of the surrounding countryside. This came to be known as the 'Tunguska event'.
If such a blast were to happen over Toronto, for example, the effects would be catastrophic. Everything from Etobicoke to Scarborough, and from the lakeshore to North York, would likely be completely destroyed, and everything else from Oakville to Pickering and north to Richmond Hill would sustain heavy damage with countless dead or injured. Also, with the object exploding in mid-air, debris would rain down across the surrounding countryside, resulting in multiple impact craters and even more death and destruction.
[ Related: 2012 DA14 flyby highlights the dangers of impact ]
Now, there's still some debate about what caused the Tunguska event. Surveys of the area have never found a definite crater or a remnant of the object, leading some to speculate that it was a comet. However, others contend that with the air burst, it may have been an asteroid that was completely destroyed in the explosion, leaving no pieces large enough to produce a crater on the surface.
If the Tunguska object was an asteroid, its estimated size and mass are roughly the same as 2012 DA14, so we can be fairly confident in using the 1908 event as an example of what would happen. So, knowing what we know from that, and also knowing that one of these objects impacts on the planet every 1,200 years or so, let's hope that we really do have another 1,100 years before the next one, since I'm fairly sure we'll have a way of preventing it by then.
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