Still frame from a dashcam video of the Russian meteor. Credit: Андрей Борисович Королев (YouTube).

If you had told me 24 hours ago that this would happen in my lifetime, I would have been skeptical–most of all that a meteoroid of this size could punch deep enough into the atmosphere to do any serious damage. If you had told me that it would happen on the same day as another major asteroid-related event, I would have done some quick mental math and promptly pronounced you insane.

And yet, there it is. At about 9:30 this morning, local time, a meteor exploded (or at least disintegrated) over the city of Chelyabinsk, Russia, population 1,100,000. The shock wave shattered hundreds of thousands of windows, set off every car alarm in the city, and, according to the latest reports, injured about 1,100 people. Thankfully, no one has been reported killed.

It’s hard to overstate how historic this is. It’s the largest meteor impact known on Earth since the Tunguska event in 1908, and, by a huge margin, it is the most damaging impact in history to human civilization. There have been a couple of confirmed reports of one or two people being injured by meteors, but never over a thousand.

(There are some records that suggest 10,000 people were killed by a meteor shower in China in 1490, but astronomers dispute this.)

So what happened here?

It seems that a chunk of space rock–or, as I suspect, mostly metal, since it took so long to burn up–slammed into the atmosphere from the northeast at about 15 kilometers per second (33,000 mph). Coming from that direction, it would have come almost directly out of the Sun, making it impossible to detect in advance. Russian scientists initially estimated that the asteroid was about 10 tons and about 2 meters wide. However, NASA later computed that it was 15 meters wide (the size of a house) and weighed 7,000 tons. I’ll spare you the math, but that works out to a kinetic energy of 200 kilotons–equivalent to a medium-sized nuclear bomb!

I’ll leave it to Phil Plait to explain just what happened to the meteoroid when it entered the atmosphere, but here’s the short version. Do you see that cloud in the first picture? That cloud is called a “meteor train”, and it’s over 300 kilometers (200 miles) long. It was visible from space. A weather satellite captured this image, which is superimposed on Google Maps:

The meteor train as seen from space compared with a map of the area. Credit: Paolo Attivissimo.

The meteor heated up as it plowed through the air until it either broke into pieces or outright exploded 20-25 kilometers (12-15 miles) above the city of Chelyabinsk, according to NASA estimates. At this point, many videos were taken of the meteor from dashboard cameras in cars. Russia happens to be a great place to get videos of things like this because so many people have dashcams in order to combat police corruption and insurance fraud. The result: this. (Seriously, some of that stuff doesn’t look like it should be physically possible.)

And then there’s this:

To reiterate, Chelyabinsk was hit by an explosion more than 10 times bigger than any weapon we humans have ever used on each other.

The flash was said to be brighter than the Sun. Within moments, security cameras and cell phone videos joined the action, but things were just getting started. With the explosion came a shock wave–or if it wasn’t a proper explosion, there was a sonic boom, and maybe more than one from the different pieces of the meteoroid. From a height of 12-15 miles, the shock wave took over a minute to reach the ground, based on the speed of sound (for comparison, you may notice that thunder follows lightning by just 5-10 seconds). So while people were busy looking out their windows at this:

Closeup showing the distinctive double train of the Russian meteor. Credit: Nikita Plekhanov.

This happened:

Most of those 1,100 people were injured by flying glass, though most probably not as dramatically as that video. The shock wave–not a solid rock, mind you, but just the shock wave–also did this to a local factory:

Meteor damage at a zinc factory. Credit: Reddit.

Take another look at that double contrail in the close-up of the meteor train. That strongly suggests that the meteor broke into two big pieces. We’re not too sure what happened from that point on, but we do know that a fairly large chuck sailed another 80 kilometers (50 miles) before crashing through the ice of Lake Chebarkul:

End of the line: a crater in a frozen lake. Credit: ITAR-TASS Itar-Tass Photos/Newscom.

But here’s the real weird part: 2012 DA14. Completely unrelated, as we can see because it came from the south and not the northeast, this three-times-bigger space rock passed safely by the Earth at a distance of 28,000 kilometers (17,000 miles)…on the same day as the Russian impact. What are the odds of that? In a word, astronomical.

A rough estimate suggests that a space rock this size hits Earth every 20-30 years. The fact that we haven’t seen one this size fall in 100 years isn’t that surprising. Earth is a big place, and we weren’t watching sky that close for most of it. Plus there is some randomness to it. Meanwhile, an asteroid as big as 2012 DA14 passes this close to Earth about once every 40 years.

But to happen on the same day? Even being very generous with allowing somewhat smaller objects into the calculation, this is a once in 20,000 years event! To include an impact in a populated area? Once in 200,000 years, at most! Forget once in a lifetime; this shouldn’t have happened at all!

So how did it happen? Well, the Solar System is a random system, and sometimes, coincidences do happen. Statistically, they have to happen eventually. (That, or the aliens were firing a warning shot, but let’s not go there.)

Which is why asteroid defense is so important. We just got hit with a once in 200,000 year combo. A once in 200,000 year event for a single asteroid would be almost half a mile wide and would pack enough energy to level an area the size of Ohio. Granted, it probably won’t happen for, well, 200,000 years, but we saw today that coincidences do happen. We’ve been making some good progress on this, but here’s hoping that after this asteroid double header, more people take notice.

(Full disclosure: I’m from Ohio, but I picked it because it’s the right size and close enough to square.)