NASA has revealed that an asteroid entered Earth's atmosphere in December and exploded over the Bering Sea with an impact energy equivalent to 173 kilotons of TNT: 10 times that of the atomic bomb dropped on Hiroshima in 1945.
It's the second time in six years that an asteroid this large has entered the Earth's atmosphere — a fairly improbable event, since NASA says meteors of this size only occur two or three times every 100 years.
Since this meteor exploded high in the atmosphere over an unpopulated area it went virtually unnoticed. But it got me thinking: what would have happened if it had exploded over a city? I can't resist a good anxiety-inducing "what if", so I plugged the numbers into the Nukemap website (which simulates nuclear blasts) to see what would happen.
As the target I chose the center of my home city, Portland, Oregon. I configured Nukemap to simulate a 173 kiloton blast at a height of 25.6km above the surface, with no radioactive fallout.
The results? Nukemap estimates 840 fatalities and a massive 220 meter wide, 50 meter deep crater. But this is a very rough and probably inaccurate simulation, since it's tuned for nuclear weapons rather than meteors.
As we learned from the Chelyabinsk meteor in 2013, damage would probably be spread along an elliptical area stretching dozens or hundreds of kilometers, and many injuries would be caused by secondary effects of the blast (damage to eyes and skin from intense light and UV radiation, injuries from broken glass and falling objects, etc).
What can we do to prepare for situations like this? Probably not much. By next year NASA is hoping to be able to identify 90% of near-Earth asteroids 140m in size or larger, but that's many, many times larger than the Bering Sea meteor and the Chelyabinsk meteor. And even if NASA can spot a large asteroid, there's not much they can do about it other than predicting where the impact will be.
Short of living in reinforced underground bunkers, we probably can't do much except hope for the best. So I guess that's one more thing that'll keep me up at night for no good reason. 😬
📷 Satellite view of the Bering Sea meteor in December 2018 (it's the tiny orange speck in the center).