BBC地平线：陨石真相大揭密

     On a bright, cold morning on 15th February 2013, a meteorite ripped across the skies above the Ural mountains in Russia, distintegrating into three pieces and exploding with the force of 20 Hiroshimas       It was a stark reminder that the Earth's journey through space is fraught with danger       A day later another much larger 14,3000 tonne asteroid, passed within just 17,000 miles of