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June 17, 2004
Celestial Engineering
I had a dream this morning that I was on an engineering team that was doing celestial engineering. We were creating a solar system with a habitable planet. To do this we used a neutron star, for some reason. I can't recall how or why we used a neutron star, except that it came in handy when we were done as the neutron star would act in much the same way as Jupiter does, sucking up rogue asteroids/comets/etc from getting into the inner solar system. It was all really cool.
When I woke up I kept thinking about planetary formation. And then I had this really funny thought: Why hasn't the earth exploded?
Read on for more...
Here's the thing: The earth's core is thought to be a molten core or iron (and nickel, carbon... heavy stuff). This molten metallic core acts like a dynamo, providing our magnetic field, which shields us from much of the nasty radiation that would make life impossible otherwise.
The thinking is that at some point the planet was under constant bombardment by stuff glomming together to form the planet. This mess of stuff was a very hot, molten blob. All the heaviest stuff sinks to the bottom of this blob, hence, we have our rather useful (mostly) iron core.
Now here's what struck me. Uranium is a lot heavier than iron. So why didn't all this uranium sink down and undergo a massive fission reaction, blowing up the planet? Scary, huh?
I think I have a decent explanation. First off, you need to know that it is believed that a shitload (that's a technical term, BTW) of radioactive stuff is in the planet's core, and this radioactive stuff is what keeps the core molten: all the heat generated by the radioactivity heats up the core and keeps it molten. But why aren't there large fission reactions?
One of my thoughts was that the molten core is more or less uniform in the distribution of fissionable materials. The thought I had was that these substances were more or less 'soluble', to some extent, in the medium of the molten core and are thus kept evenly distributed. This would keep large fissionable gloms of stuff from coming together.
However, I didn't think this was all that plausible, at first. So I started thinking along the lines of 'What if there were blobs of fissionable stuff bubbling around in the core?' This isn't so crazy. 'But Ed', you ask, 'Why then hasn't the planet blown up?' Ah! Here's the thing. What if there were blobs of stuff coming together and reacting? The thing is, these masses of stuff aren't like an atomic bomb. In a bomb, the material is in chunks, which by themselves aren't critical (they aren't going to undergo an uncontrolled reaction and blow up), but when they are forced together and compressed by an external force (conventional explosives) they undergo an uncontrolled fission reaction and *KERBLOOEY*, stuff blows up. But in this molten soup of iron in the core this stuff can't do that, really. When a bunch of stuff starts coming together it could possibly undergo fission, but the very first initial reaction/explosion would immediately diffuse the rest of the stuff, so a really big explosion can't happen. Plus I think that the heat from all this stuff must create thermal eddies and currents in the core which keep the stuff pretty well mixed up.
So, all in all, I think we are probably safe from the planet blowing itself to smithereens.
Still, I have to wonder if any small fission reactions have taken place in the core. I would think that seismic sensors would be able to detect this sort of thing, so maybe it doesn't happen often. But what if it did? Wouldn't this cause 'bubbles' of reaction products to surface from time to time? I wonder if it would be possible to detect the products of these reactions somehow...
Anyway, I'm glad I got all that off my mind.
Posted by ed at June 17, 2004 9:56 AM
Comments
Wow, your blog makes me feel dumb. But when I read the Bad Joke of the Week, then I feel like the smartest person alive!
Posted by: Linda at June 17, 2004 6:08 PM