The Guardian:

An asteroid that exploded last year over Chelyabinsk, Russia, leaving more than 1,000 people injured, collided with another asteroid before hitting Earth, research by scientists shows.

"This impact might have separated the Chelyabinsk asteroid from its parent body and delivered it to the Earth," lead researcher Shin Ozawa of the University of Tohoku in Japan wrote in a paper published this week in the journal Scientific Reports.

The guess is that this collision happened in some deep part of space 290 million years ago—humans were not around at this time. Its explosion over Russian skies is estimated to have had 30 times the force of a nuclear bomb. When the fragments entered our atmosphere 290 million years after the fateful collision, the world could not tell which was more bizarre: the suddenness of all those bright streaks and flashes or the radio programs and music that Russians listen to as they drive...