Thursday, September 1, 2011

Will the Fragments of Comet Elenin Rain Doom upon the Earth? (No, but You Knew That)

File:PIA08452.jpgThe disintegration of comet 73P (not Elenin). Image Source wikipedia commons.

Now that Elenin is disintegrating, some people are worried that chunks of the disintegrating comet will hit Earth. But what people fail to realise is that space is really, really, REALLY big.

That sounds a bit patronising, but is actually very hard to get a good grip on the distances involved, the mind reels from the vastness.

To get a feel for what the distances are like, try this demonstration.

Get a pea, a peppercorn and a mustard seed (or objects with those rough general dimensions). Put the pea on your back doorstep, that’s earth. With a ruler measure out 384 mm and put the peppercorn 384 mm away from the pea, that’s the Moon. Now pace out 35 meters (yes, you read that right 35 meters), that represents the closest approach of Elenin to the earth. Put the mustard seed there (it’s actually much bigger than Elenin would be at that scale, but it’s the smallest object that you can actually work with).

Now, get a hammer and smoosh the mustard seed to a powder. Look at how far the powder flies from the mustard seed*; look back the 35 meters to the Earth.

Any questions?

* When comets break up, most of the material stays on much the same orbit as the parent comet (see image of 73P above as an example). Over the years it will spread out a bit, but for Elenin the material won’t move far enough away over the next few weeks to register on our model. Even if Elenin had undergone a DeathStar like dramatic explosion, rather than the gentle sigh and crumbling, the vast distances involved would mean that the material would not impact the earth.


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