It was one of those awful coincidences. Last Friday evening I was having a few beers with a friend, in a local pub. He was calculating the likely impact energy if 2012 DA14 – due to make a close pass over Indonesia – were to ever hit us.
Earth. An image I made with my Celestia installation (cool, free, science package).
There are websites with Java script that do this, but it’s easy yourself if you have figures for velocity and mass – a function of volume and density – plus the formula and a calculator. (Yes, I know it had been published, but it’s fun to do the math. I’m a geek and so are my friends. Remember…geeks won….)
Nobody realised another object was about to explode over Chelyabinsk – ‘Tankograd’ of Second World War fame.
The 1200 injured from flying glass is the largest human toll recorded from a meteor strike. The cost to Russia will be in the millions of roubles. Not to mention the fact that thousands of people are facing sub-zero temperatures in windowless homes, until they can be fixed.
All that because the Pope resigned. Well, it’s obvious. The Conspirating Ruling Archaic Poodles, a secret cabal nobody has ever heard of, used their stooges to drop one of their orbiting Bombs Utilising Low Level Seekrit Hyper Invisible Termination on the Vatican, thus covering up the Pope’s resignation, but because secret organisations always make basic arithmetical errors, it hit Russia instead. I have proof this is true, because they fly in invisible black helicopters. Well, have you seen one? Quite. Proves they exist…
And yes, I know that is a really, really stupid theory…but hey, it’s not the dumbest one out there.
Needless to say, the science involved actually answers all questions. First off – the energy involved is mind-blowing on the scale of us mere humans.
How mind blowing? Try this. The Russian rock was maybe 10,000 tonnes mass and 17 metres diameter, by NASA estimate. Yet still exploded with an energy equivalent, some estimates suggest, of around 500,000 tons of TNT. How come?
Well, it’s entirely to do with kinetic energy, which you calculate according to the formula 1/2 MV<exp>2. It was moving at over 63,000 km/h when it hit the atmosphere. That gave it a kinetic energy (roughly) of around 500,000,000,000,000 joules. Translated into human terms, that’s what a 1-kilowatt fan heater would emit if run constantly for 15,844 years (it would run out in about March in that last year).
That’s a lot of energy. So why did it explode? At the speed this sucker hit us, it was moving so fast it couldn’t push the atmosphere out of the way. The air was compressed ahead of it, got super-hot, and then began vapourising the front side of the meteor. But the back side was still ice-cold. After a while, differential thermal stresses exceeded the tensile strength of the object – and boom! A lot of the kinetic energy translated into a massive shock wave, shattering glass over that huge area, and powerful enough to be detected in Alaska. Some became heat. Some was retained in the fragments of meteor that hurtled into the ground, which will be found sooner or later (they’re looking now).
The take-home lesson from Friday? The odds of a damaging meteor hitting us, by human time-spans, are low . But these things do happen. And we didn’t see this one coming despite a determined effort of late to detect everything in our vicinity that might be a threat. We’ve even found the S-1VB stage from Apollo 12, which is lobbing around in a weird orbit nearby. But Friday’s rock – still a city-buster – was too small.
A Hubble picture of Jupiter after it had been machine-gunned by Comet Shoemaker-Levy in 1994. NASA, public domain, via Wikipedia.
Worse, even if we had seen it, there was nothing we could have done. The laws of physics are clear; Bruce Willis and a gang of Texan oil-riggers aren’t going to save the day at the last moment. I’ve explained why in an earlier post – check it out. Even if you could carry enough rocket fuel to get to an incoming rock and blow it up (which you can’t….trust me…) most of the bits will still hit the Earth with the same net kinetic energy. And it’s that energy that’s the problem.
That doesn’t mean we can’t find ways of handling it. Given decades of warning, even spray-painting the side of a space rock black will work, by changing the way it re-radiates solar energy, asymmetrically. Over years, that will change the orbit.
Of course, space debris usually isn’t isolated. A comet can break up, leaving trails of objects following its original orbit. Jupiter was slammed by just such a train ‘o doom in 1994. There’s a fair chance that we might have to try and deflect half a dozen potential impactors all at once.
Personally I’m not going to lose sleep over it. No point worrying about things we can’t control. And the prospect of being slammed by a space rock is pretty far down the list. Here in New Zealand, for instance, it’s more likely we’ll be hit by an earthquake – in fact, there was a small one in my city on Saturday and another tremor this morning.
What’s your take? Should we worry about that which we cannot control? Or get on with life?
Copyright © Matthew Wright 2013
‘Kindness 2013’ returns next week. Coming up this week: more sixty-second writing tips, Write It Now part 6 – and more.
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