How to bump an asteroid off course

Roughly every other week a one-metre-wide asteroid impacts on Earth's atmosphere and creates a spectacular fireball. Meanwhile, every few decades a lump of rock the size of a double-decker bus comes our way, creating a small crater on the ground like the Russian Chelyabinsk event on 15 February 2013.

Asteroids that cause significant damage (football-field-sized rocks) slam into us every 5,000 years or so, and the real biggies - capable of causing global disaster - arrive every few million years.