As seems to be my want at the moment, today I have another disaster-oriented column for you.
Remember the recent meteor event in Russia? On February 15 this year a rock estimated to be 50 meters wide and weighing an estimated 10,000 tons entered the atmosphere over the city of Chelyabinsk at a speed of around 40,000 mph and exploded.
The shock wave was estimated as having the power of 50 kilotons of TNT and injured about 1,500 people. It also rather pointedly raised the question of how well prepared are we for dealing with meteors. The answer is that we really aren't capable of doing much at all (although we have lots of ideas that probably aren't practical).
For a start, we really don't know what's out there. While there are some pretty impressive programs for finding and identifying asteroids, for example, NASA's Near Earth Object Program, none are funded nearly well enough given that these chucks of rock could cause immense damage to our planet up to and including wiping out life on earth.
While forewarned can be forearmed, when it comes to asteroids even if we knew that some piece of space debris was heading our way other than trying to evacuate people in its path (imagine trying to get people out of New York or, worse still, Mumbai) the current reality is that we'd be pretty much out of luck.
To get a better handle on the degree of risk we face from meteors it's worth looking back to see how what kind of (if you'll excuse the pun) impact they've have had on the earth in the past. A new mashup using data on known significant meteor strikes over the last 100 years does just that. Fireball from Outer Space by Sebastian Sadowski plots 606 eye-witnessed events worldwide which you can filter by country and date.
The Fireball historical meteor strike visualization
The biggest meteors over the whole time period covered by Fireball are Sikhote-Alin, 23 metric tons (Russia, 1947), Jilin, 4 metric tons (China, 1976), Allende, 2 metric tons (Mexico, 1969), and Norton County, 1.1 metric tons (United States, 1948). But none of those compare to the 1908 Tunguska event which was not witnessed by anyone as it occurred near the desolate Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia.
The reason we know about Tunguska event is due to the incredible damage it caused (770 square miles of forest was flattened) and it's estimated that the blast was equivalent to between 10 and 15 megatons of TNT (that's about 40 percent of the blast of the Tsar Bomba I discussed in my recent post What would a nuclear blast do to my town? concerning another mashup that simulates nuclear bomb explosions).
The aftermath of the Tunguska event
Another excellent meteor visualization is 500 Years of Witnessed Meteors by Adam Pearce. As it's name suggests it covers 5 centuries of observed meteor strikes. This interactive presentation actually has photos of the meteors (or fragments thereof).
500 Years of Witnessed Meteors visualization
Fireball and 500 Years of Witnessed Meteors are beautiful pieces of work that were created as entries to visualizing.org's Visualizing Metorites competition and the actual winner of the competition was Macrometeorites by Roxana Torre.
Macrometeorites is stunning and it's timeline animation is way cool. Keep in mind is that the visualization starts from 1399 so the apprent speed up of witnessed meteor events is due to better communications and a growing population and not that the rate of meteor strikes increased.
After playing with these visualization you might conclude that meteor strikes of any significant size are pretty rare events (from a total of more than 45,700 recorded meteorite landings only around 3,800 have a mass larger than 1kg) and you'd be right as long as you're talking about those that are are actually witnessed by people.
If you take a more realistic view you'll realize that there are huge tracts of the earth's land where nobody lives (depending on who you believe that's roughly 90% of the planet) so the apparent clustering you'll note is undoubtedly related to population density. So, let's assume that because of clustering something like 50% of impacts are not witnessed ... that makes the total of significant strikes for the last century around 1,200. But wait ...
There's also the oceans where impacts undoubtedly happen with equal frequency to land events. Given that oceans are 70% of the earth's surface. It would seem reasonable that there were as many events at sea as there were on land over the last hundred years making the real total at least 4,000 significant events. The risk of significant meteor impact events may be much higher than is generally appreciated.