Another day, another stupid asteroid scare

The road I live on has a railway running across the end of it. Every day, hundreds of tons of metal speeds along the line just a hundred metres or so from my house. Yet I don’t live in fear of waking up one morning and finding a train’s crashed into my house, because of course the trains are restricted to the railway tracks.

Space is much the same. Asteroids are whizzing around over our heads every day, but they follow precisely defined orbits through the sky. An asteroid passing close to the Earth is no more a “near miss” than a train passing my house without hitting it is a “lucky escape”.

It’s a simple enough idea, you’d think, and yet…

“Phew, that was a near miss: Cigar-shaped asteroid stronger than ’15 atomic bombs’ whizzes by earth”

Thankfully, the 50m long rock that could have destroyed a small country went barely noticed as it passed earth at a distance of some 2,085,321 miles.

Yes, the asteroid 2011 GP59 could have destroyed a small country. If it was two million miles closer.

Once again, this article has been taken from the Australian news site news.com.au, who seem to have a thing for scaremongering stories about space; they also started the rumour that Betelgeuese would go supernova in 2012 and gave credence to the shameful “supermoon” story. At least the Mail‘s headline is less awful than news.com.au’s, who’ve gone with “Scientists find asteroid with potential power of 15 atomic bombs. Heading this way. Tonight.” which surely has to rival shouting “fire” in a crowded theatre in terms of unethical scaremongering stupidity.

Incidentally, the claim that it’s “as powerful as 15 atomic bombs” doesn’t come from any scientific authority. It comes from the news.com.au journalist – who doesn’t appear to be a science journalist at all, but a technology journalist – digging up an old New Scientist article about an asteroid that exploded with the energy of three nuclear bombs (three of the very small Hiroshima bombs, I should point out, not a modern nuclear bomb), and then scaling it up. This is a stupid calculation for a number of reasons:

  1. You can’t just say “this asteroid is 10 metres long, this asteroid is 50 metres long, therefore it’s 5 times bigger”. It’s the volume which is important – the length times the width times the height. Assuming the asteroid is 5 times bigger in each direction, then it’s 5 x 5 x 5 times bigger, which is 125 times the size. If the journalist hadn’t cocked up his maths, he could have made this asteroid sound EVEN SCARIER. Except…
  2. The amount of energy an asteroid has depends on its speed. A fast moving asteroid carries far more energy than a slow moving one, and a small increase in speed causes a much larger increase in energy.** The gravitational pull of the Earth as the asteroid approaches plays a large role in determining its speed, so the energy it would have would depend on the route it took to Earth. Since this asteroid is not heading for Earth, it’s meaningless to ask how much energy it would have if it hit Earth.
  3. It also depends what the asteroid is made of. Most asteroids are made of dust and ice, and burn up harmlessly in the atmosphere. A few – maybe one per year – explode high up in the atmosphere. And a very, very few – mostly large metallic asteroids that don’t burn as well –  hit the ground. Again, we don’t know what this asteroid is made of.
  4. THE ASTEROID IS TWO MILLION MILES AWAY AND WILL NOT HIT EARTH AT ANY TIME IN THE FORESEEABLE FUTURE.

At any rate, there are literally thousands of asteroids this big – or indeed much bigger – rattling around near-Earth space, and there must be thousands more we haven’t detected yet. It’s worth being sensibly worried about the risk of currently undiscovered asteroid hitting us, but getting worked up about an asteroid that we know can’t hit us is just stupid.

Now, if you’ll excuse me, I’m off to dig a train-proof bunker in my garden.

* Psst, Daily Mail Reporter. “Earth” has a capital “e”.

** In fact, energy is proportional to speed squared – if you double your speed, your energy goes up fourfold.

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  1. #1 by ukenagashi on Sunday, 17th April 2011 - 8:34 UTC

    I just want to say I find your level-headed sciencetalk super hot.

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