The explosion of an asteroid over Chelyabinsk, Russia, back on February 15th, was impressive and more than a little bit scary. However, a new study of this event, along with similar ones that have happened in the past, reveal that we may have underestimated the overall threat of these impacts.
When a 20-metre-wide, ten-kiloton asteroid entered Earth's atmosphere in mid-February, it created a superbolide meteor streak through the air above Russia before exploding roughly 20 kilometres above the city of Chelyabinsk. The explosive power of this 'airburst' was estimated as equivalent to detonating over 400,000 tons of TNT, roughly the same as just one of the warheads that's carried by modern nuclear missiles. Even from that far up in the air, the shockwave from the explosion still shattered windows across the city and surrounding area, and nearly 1,500 people were injured.
A new study of the asteroid's trajectory showed that it made a very shallow dive into our atmosphere, which limited the amount of damage the explosion could have done. This computer simulation, by Sandia National Laboratories physicist Mark Boslough, shows the expanding shockwave from the explosion as it happened, and then shows a hypothetical case if the asteroid came in a much steeper angle:
With the steeper angle, the asteroid would have exploded much closer to the ground (maybe 12 kms up), the shockwave would have reached the ground sooner, thus it would have contained more energy, and it would have ended up doing more damage.
Looking at this case, along with what's known about the 1908 Tunguska event, and another bolide explosion in August of 1963, over the Prince Edward Islands, about 2,000 km off the southern tip of Africa, Boslough suggests there are more of these dangerous asteroids out there than we think, and that the hazard from these asteroid airbursts is higher than we thought too.
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Part of the reason for the number of injuries was people crowding around windows to see the event, which even Boslough — as knowledgeable about airbursts as he is — admitted he probably would be doing too. Still, if we could be warned about these asteroids ahead of time, more people could take cover and avoid injury.
There's still another aspect of the Chelyabinsk event that has Boslough worried, though. It's the potential for one of these airburst explosions to be misinterpreted as an attack by a foreign power. February 15th was a clear, sunny day over Chelyabinsk, so everyone saw what caused the explosion. However, as Boslough said to Space.com: "Say that this had happened on an overcast day, where nobody actually saw the streak across the sky. Then you see smoke, hear a large explosion and a lot of things that sound like artillery fire. One of the biggest threats could be that this might lead to a counterattack of somebody because something was misconstrued."
(Photo courtesy: Reuters)
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