Last Friday, a meteor hurtling through the Earth’s atmosphere at 10 to 12 miles per second exploded thirty miles over the Chelyabinsk region in the Russian Urals. People saw the flash of light and rushed to the windows to look—which was exactly the wrong place to be when the shock waves that followed shattered windows, injuring about a thousand people. The meteor was estimated to be about the size of a minivan.
The last time an object from space caused such mayhem was in 1908, but it’s not a very well-known event. More on that later.
A meteor, by the way, is a space rock that enters the Earth’s atmosphere and burns up. A meteorite is a piece of meteor that actually hits the Earth. If you visit the American Museum of Natural History in New York, go see theirs. They have some cool ones. Here’s a famous meteorite from Denmark:
The How Stuff Works website has a good explanation of shock waves and sonic booms and how they work. Think of standing on the shore of a smooth lake when a motorboat zooms by. At first there is no disturbance, but soon after (depending on how far away you’re standing), the wake from the boat rolls onto the shore. It’s similar with a plane flying past, and if an object is going faster than the speed of sound, you get a sonic boom.
How big does the meteor have to be to cause planetary mayhem? Much depends on the area of impact. (But note that when scientists use the word “impact,” they don’t mean it has to hit the Earth. It just has to explode close to the Earth’s surface.) The one that caused the Cretaceous Extinction 65 million years ago was probably seven miles across. That’s, um, a biggie. But there was a more recent near-disaster.
On the morning of June 30, 1908, a meteor about 120 feet across (one scientist described it as “about the size of the White House”) entered the atmosphere over Tunguska, in Siberia, and then detonated in the sky. Over eight hundred square miles of trees were destroyed, along with a lot of reindeer. But as “Siberia” has often been interchangeable with “the middle of nowhere,” there were very few eyewitnesses. Here’s where it happened:
Scientists estimated that the space rock was traveling at a speed of about 33,500 miles per hour. At a height of about 28,000 feet, the combination of pressure and heat caused the rock to explode, producing a fireball and releasing energy equivalent to about 185 Hiroshima bombs.
According to the Guinness Book of World Records, if the collision had occurred just 4 hours 47 minutes later, it would have destroyed the city of St. Petersburg.
Why do so few people know about this massive meteor event? Russia was a fading, ill-run country; it had recently lost to Japan in the Russo Japanese war in 1904-5, and the power of the Romanovs was in serious decline. The Trans Siberian railroad wouldn’t be completed until 1917, so travel to the site was nearly impossible. At the time, there were few to no roads to that region, so in summer travel was limited to rivers, and in winter, to sleighs. Then there was World War I, the Russian Revolution of 1917 and subsequent Civil War, and a major flu pandemic, so it wasn’t until 1921 that a scientific expedition visited the site.
So should we all be worried it could happen again? Well, yeah, it’s certainly possible. But I think in the scheme of things, we have more urgent problems for our planet to be concerned about. As for me, I don’t plan to watch any Hollywood disaster movies on the topic anytime soon.