Bright Visitors 
The asteroid that rattled central Russia back in February was the largest known to hit our planet in more than a century. But slightly smaller space rocks hit Earth all the time. They’re big enough to create brilliant fireballs, rattle windows, and leave trails of debris. But they’re not big enough to threaten life and limb.
One streaked across California back in October, dropping fragments on the city of Novato. And an even bigger one punctuated California skies one year ago today. The brilliant fireball raced above the Sierra Nevada, creating a sonic boom that reverberated through the mountains. It shattered high above the ground, raining tiny bits of debris in the area around Sutter’s Mill, the site that kicked off the California gold rush in 1848.
The pyrotechnics are the result of an asteroid’s great speed. It hits the upper atmosphere at tens of thousands of miles per hour. Friction with the atmosphere creates a trail of superheated gas that glows brightly.
Although the air is simply wisps of gas, to a fast-moving asteroid it’s almost like a brick wall. The asteroid decelerates rapidly and is squeezed by the resisting air. That pressure causes the asteroid to explode. The Sutter’s Mill asteroid was probably about the size of a minivan, but it was moving at more than 60,000 miles per hour. At that speed, it released a huge amount of energy - the equivalent of several thousand tons of TNT.
Script by Damond Benningfield, Copyright 2013