Defending Earth against dangerous asteroids: Q&A with NASA’s Lindley Johnson

It’s a cosmic roll of the dice. There’s no doubt that a major asteroid or comet strike could cause extensive devastation and profoundly affect life on Earth.  The largest hit in recent times was the object that exploded over Tunguska, Siberia, in June 1908 with an energy impact of five to 15 megatons. Then there […]