It’s rainin’ rocks
This map should make us all take a moment and go hug the atmosphere. No, you figure out how, it earned it.
When a rock enters earth’s atmosphere, it releases a lot of energy and often explodes, producing shock waves in the atmosphere that have been detected by a U.S. Government monitoring program. These events are called bolides, and this map shows the location of bolides beyond a certain size in Earth’s atmosphere over a 20-year period from 1994-2013.
This map shows a total of 556 events, basically 1 every 2 weeks, on average. The largest explosion in that time was the Chelyabinsk event in 2013, when an asteroid about 20 meters in diameter entered the atmosphere, exploded, and fragmented, damaging cities in Russia near the shock.
The smallest dots on this map are much weaker than Chelyabinsk – objects about a meter in size entering the atmosphere and vaporizing or exploding produce them. Those are pretty harmless most of the time, but they still release the same energy as 5 tons of TNT exploding. The difference between a barely-detectable blast and something that can severely damage a city, therefore, is the difference between a chunk of rock 1 meter wide versus 20 meters wide - the Chelyabinsk explosion is estimated to have released the same energy as a 500 kiloton nuclear bomb.
As Earth orbits around the sun, it is literally in a shooting gallery of debris; rocks left over from the formation of our solar system hit this planet all the time, as this map shows. The locations of these events appear random, indicating that stuff flies in from all sides with no obvious pattern. By having this data over a 20 year period, scientists will be able to use statistics to estimate how often we can expect large explosions, the scale of Chelyabinsk or larger, in the atmosphere, and use that understanding to gauge how much we need to prepare for larger impacts.
If it weren’t for our atmosphere, most of these rocks would be hitting Earth. Instead, the thin layer of air above it does a remarkable job at keeping things off our heads. We owe it some thanks for that favor.
-JBB
Image credit: NASA/JPL http://neo.jpl.nasa.gov/news/news186.html