Reassessment of Air Burst Damage after Chelyabinsk Meteor Indicates Much Higher Risk
A new paper published in the November 6th electronic edition of Nature indicates that we are in greater danger of injury from asteroid "impact" than we have realized. The primary increased risk is due to the understanding that smaller objects can cause far more damage than we realized. The Chelyabinsk Meteor airburst caused an explosion that was equivalent to 500kt of TNT, it was a relatively small sized rock of 20 meters, and the primary explosion occurred about 30 km above the surface of the Earth, but the damage to the city of Chelyabinsk and its surrounds was extensive. Damage occured in an area 90 km to either side of the path of the meteor and more than 1,600 people were injured (mostly from flying glass).
Up until now, scientists at NASA have assumed that a rock less than 30 meters in diameter would harmlessly break up in the atmosphere, and while this may be true, it's now quite clear that an airburst actually can cause a fair amount of damage. There is somewhat of an inverse exponential relationship between the diameter of a space rock and the number of space rocks that fit that diameter in space. Tiny dust grains in space are innumerable, dwarf planets like Ceres are rare, but not as rare as planets. 30m diameter objects are much less prevalent than 20m objects. To make matters worse, it's much harder to find the smaller asteroids before they have a chance to cause us harm. The studies indicate that the increased risk of asteroid damage is now on the order of 10 times worse than expected. While this sounds shocking, please keep in mind that the overall risk of personal asteroid damage was quite small to begin with (almost trivial). Now we know the risk is not so trivial after all.
Links for this story:
Univ of Western Ontario CPSX Chelyabinsk Story
Older Paper on Chelyabinsk Meteor
In case you'd like to read the Nature paper at a cheaper price.
Video illustrating the delay between meteor and shockwave
Compilation of Russian Videos of the Airburst