The Meteor Threat
We think a meteor hitting the Earth killed off the dinosaurs 65 millions years ago. Other impacts in Earth's history include Tunguska, Siberia, in 1908, and the impact the caused Meteor Crater in northern Arizona. But what, realistically, are the chances that this will happen to us? Regardless of the actual probabilities of impact, any fear produced from the threat of another meteor producing a similar catastrophe is perfect fodder for a sensationalism-style media and a Hollywood industry that places entertainment and profit above scientific facts (see the links on the 1998 impact movies "Deep Impact" & "Armageddon"). Public relations between scientists and the media is tricky on this issue, as proven in the Asteroid 1997XF11 scare of March 1998.
Not to downplay the risk, but many people do not understand the actual probabilities involved-- Typically, the chances of a massive meteorite hitting the Earth are around 1 in 1-10 million. Try this experiment at home: Pick a number between 1 and 10,000,000 and have a friend take one guess at it; how often does your friend guess the correct number? You probably stand a greater chance of winning the lottery jackpot or getting struck by lightning than by a meteor during your lifetime.
In other words, however large a meteor may be, there's a large volume of space out there, and plenty of room for all the objects in our solar system. Still, there does exist a number of potential catastrophe-causing meteor hazards out there, leading the U.S. Congress to debate a billion-dollar 'asteroid defense' system of protection using missiles. Here are some articles and sites dedicated to these 'minor planets' and the possibility of their collision with Earth.