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Asteroid on Collision Course with the Earth ?
Science fiction movies such as Armageddon, Meteor, Deep Impact, and When Worlds Collide show various scenarios where items in space are on collision course with the earth. How realistic is that? Ask any dinosaur and they'd say that it never happens. But surprise they were taken by! It has been suggested that the extinction of the dinosaurs, (and therefore the allowing of the creation of humankind), was caused by an asteroid impact.
Small impacts, in the ten megaton size range, hit the earth every few decades. It is a matter of luck that on average these things hit places like Tunguska (almost no population) rather than cities.
Very small impacts (the size of
the Hiroshima atomic bomb) hit every few months and sometimes put
the nuclear defence systems on alert! (Not that the nuclear
defence systems are pointing at the impacter - it's pointing at
opposing tribes on the earth).
It would be a very good idea to have an advanced space program, so as to avoid going the way of the dinosaurs. Colonising other planets would be good for survival, but also having space-going technology improves the chance of being able to deflect asteroids away from the earth.
A few good contacts in this business:
Spaceguard Centre (Powys, Cymru/Wales)
Also see Astronomy Hotels
Comets and Asteroid Information Network
Lord Sainsbury's Near-Earth Object Task Force Report
Also, a Google Search for "Minor Planets" sometimes finds helpful contacts.