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Mitchell_Porter comments on Open thread, February 15-28, 2013 - Less Wrong Discussion
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This was my thought process: Let's suppose that a "closest asteroid observed" record happens once every few years. Now suppose that a once-in-a-century fireball is going to happen. What are the odds that it will happen on the same day as a "closest asteroid observed" event, assuming that the latter are independently distributed with respect to fireball events? About 1 in 1000 (order of magnitude). And then I chose 1 in 500 as a representative probability that is greater than 1 in 1000, that's all - it didn't derive from any reasoning about orbital mechanics, it was chosen to illustrate the possibility that "natural but related" might be more probable than "natural but unrelated".
But how could the "related" probability be that low? Well, the solar system contains all sorts of weird orbital resonances. Maybe there are multiple earth-crossing orbits which for dynamical reasons cross Earth's orbit at the same point, and on this occasion, there was debris in two of these orbits at the same time.
The Chelyabinsk meteorite wasn't anything like "once-in-a-century". Off the top of my head, here's a couple recorded a few years ago:
http://www.youtube.com/watch?v=pRtucs6D0KA
http://www.youtube.com/watch?v=8q3qWV4Ks3E
And that's just events in inhabited areas witnessed by people with a camera. Most of the Earth is either ocean or uninhabited wilderness, so it stands to reason that most such events will go unrecorded.
The first video doesn't show a meteor, it shows trails from a plane, lit by the setting sun.
As for the second one... "The meteoroid ... is estimated to have been about the size of a desk and have had a mass of approximately 10 tonnes."
Compare to the Chelyabinsk meteor: "With an initial estimated mass of 10,000 tonnes, the Chelyabinsk meteor is the biggest object to have entered the Earth's atmosphere since the 1908 Tunguska event, and the only meteor known to have resulted in a large number of injuries."