Colliding asteroids
If you've been reading any science news today you have probably already heard that a new estimate of asteroid impact rates suggests that Tunguska-like events (the asteroid impact in Siberia in 1908) are likely to occur about every 1000 years, much less rarely than previously thought. (Note: there are bound to be people out there who think this means that we are safe for another 906 years, but seeing as you know more about statistics, you know the actual date of next impact could be any time from now on...) The part you may not have read in the news reports is that the uncertainty in the 1000 year value is quite large with the range of 800-1800 years or 400-1800 years depending on which asssumptions you make. Still, this study is a better estimate than previous attempts to quantify the actual impact rate.
