Once a Century, On Earth…


[I’ve updated this post with the latest numbers, which push this back from the “once a decade” category to the “once a century” category.]

This event is becoming more and more extraordinary.

You’ve probably seen video over the last few years of fireballs passing overhead – I remember there was one from a Texas police car’s dash cam – but note that in all those cases, there was no “boom,” and no significant piece actually hit the ground (often, nothing beyond dust.) Reports of “craters” and such were typically misidentifications or hoaxes.

And typically, the rocks involved were probably just a few inches across. That seems small, but you have to imagine the incredible amount of energy that’s released when something traveling tens of thousands of miles per hour slams into the atmosphere.

So. “Typically.” This morning, we got “Extraordinary.”

Here’s a note from astronomer Dr. Heidi Hammel written very soon after the event:

What we know (subject to change as more information comes in): At 9:20 a.m. local time in Russia, videos shows an impactor coming in from the North. Asteroid 2012 DA14 is approaching Earth from the South. These two events are not related. According to asteroid expert Rick Binzel at MIT, the body is estimated to have 2 meters (6.5 feet) across, about the size of an SUV, weighing roughly 10 tons. The resulting airburst would have the equivalent yield of a 1-10 Mton explosion. These are very rough and extremely preliminary estimates. Early reports suggest that substantial fragments made it to the ground after the airburst, suggesting that this was an iron-nickel asteroid, rather than a stony asteroid or comet (no fragments were ever found from Tunguska). A much more quantitative estimate will come from analyses of the videos, the damage distribution, the seismic reports, etc. The timing of the shock wave, and the verbal and video reports, are consistent with verbal reports of the Tunguska event in 1908.

Since this was written, others have pegged the size of the blast as closer to 100 500 kilotons (half a megaton,) rather than 1-10 megatons. And the rock was probably closer to 17 meters (55 feet) in diameter.

The explosion probably happened around 18 10 miles or so above the surface of the Earth, as the meteor hit the first “solid” part of our atmosphere while going 11 miles per second. The amount of energy released when a solid object hits the atmosphere at that speed is hard to imagine.

What we’re hearing in the videos, and the damage we’re seeing, is sort of like what would happen if a bomb about 5 30 times as large as the one that devastated Hiroshima was detonated in the upper atmosphere.

Let that sink in.

To be clear: this is only a comparison of the blast felt. Unlike a nuke, when a meteor explodes in the atmosphere, there is NO radiation involved.

And some sizable chunks may have made it to the ground. This is very unusual.

Here’s more from Dr. Hammel:

What I have been telling people (feel free to use): In my “cosmic collisions” talk (which I’ve been giving for over a decade now, since SL9), I describe the Tunguska event, and show impact statistics. One of these ~Mton events occurs roughly every 100 years. Tunguska was 1908. I ask the audience to do the math. This event was only a question of when, not if, and could have been anywhere on Earth. NASA has programs to detect potential impactors, but due to funding limitations, these searches has been focusing its efforts only objects that would cause truly catastrophic events. LSST will likewise focus on larger bodies. Fortunately, this 2013 event was not a catastrophe, just a Really Bad Day in Russia.

After SL9 and these wake-up calls of 2012 DA14 and the newest Russian meteor blast, if we humans are done in by a rogue asteroid or comet, we have only ourselves to blame. We have the technology to avert such a disaster. That said, we probably can’t stop these smaller ones from hitting Earth, since they are much harder to detect ahead of time. We can, however, give folks a few hours warning. A tornado siren does not stop tornados, but it gives people a chance to take cover. Had the folks in Russia been given even a few minutes warning, many injuries could have been avoided.

The last time a megaton-level event happened was in 1908, also in Russia (in the far eastern part.) That event was significantly larger, however, flattening a whole forest of trees. It’s fortunate that today’s meteor was smaller than the one from 1908.

Spare a thought about the planet we’re on today. And remember that none of us would be here if another, much larger object hadn’t smashed into the Earth and led to the extinction of the dinosaurs.

Could the same thing happen to us? We are the first generation of creatures on this planet with the ability to actually prevent our extinction by a cataclysmic impact… but only if we have enough warning. And that costs money. In the scheme of things, a very small amount of money, but still hundreds of millions of dollars, and euros, and yen, and yuan. We saw this morning why maybe we should go ahead and spend that money.

And now, a quick collection of videos and links:

From a dashboard camera, we see it enter the atmosphere:



Here are some videos of the shockwave reaching the ground. Very intense.

Why does the shockwave take so long to reach the ground? Because it has to travel the 18 or so miles down through the atmosphere. It’s the same reason you see lightning and then hear the thunder afterwards.




Leave a Reply