91热爆 Radio 4 - The Forum, Peering into Space, Asteroids threat: "Eventually our number will be up"

Asteroids threat: "Eventually our number will be up"

Asteroid hunter and former NASA astronaut Edward Lu says there are one million near-earth asteroids large enough to destroy a major city. Less than one per cent have been found and mapped. Lu says deflecting an asteroid is relatively easy if you know it's coming.

14 August 2013