Figure 1.15Explosion of the Chelyabinsk meteor above central Russia on Feb 15, 2013, released 20–30 times more energy than the Hiroshima atomic bomb, and its shock wave injured 1,500 people. This small asteroid had a diameter of about 20 meters and weighed about 11,000 tons, a reminder that Earth is an open system that continues to exchange both mass and energy with the solar system.