Boston - It was a normal Friday morning in the industrial city of Chelyabinsk, Russia. Adults were on their way to work, and children were in school. But that ordinary day was about to become extraordinary. Suddenly, a fireball shot across the clear morning sky leaving a thick trail of smoke, accompanied by the sound of a huge explosion. The shock wave knocked people over, shattered glass, and collapsed a factory roof. As many as 1,200 people were injured. A global network of infrasound sensors designed to pick up nuclear explosions calculated that the boom was 30 to 40 times...