But think again: The Earth has been around for 4.5 billion years -- which is 1.6 trillion days. So the chance that these two events would happen on a day sometime in the earth's history is actually larger than we first thought -- it ought to have happened about 12,000 times already.
Of course, during most of that 4.5 billion year history, the earth was not populated by intelligent life -- human beings who might have noticed the two events happening on the same day.
So what is the probability that the meteor hits and the asteroid passes Earth on the same day when someone could record it on video? That's probably been possible for about 50 years, or only about five years if we have to do it on a smartphone or dashboard camera. That's 1,825 days, which means the chance of someone filming the event is only about one in 70,000 -- and that's if people blanketed the Earth. Given how sparsely the Earth is populated, we should correct this number downward by a (large!) geographical factor. It's also unlikely that this event would happen within 3,000 miles of the Tunguska impact.
What to think? Our rough calculation says a large meteor impact on the same day as closest passage of the DA14 asteroid is really improbable. But it did happen. Something in our assumptions could be wrong. For example, the frequency of meteor impacts could be much larger and our estimates too low because we don't notice most of them.
Then again, maybe sometimes, long odds just pay off.
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