Horizon: The Truth about Meteors

On February 15, 2013, a meteor exploded over Russia's Ural mountains and sent fireballs blazing to the ground, injuring more than 1,000 people. Just a day later, an asteroid passed within 17,000 miles of Earth. These were reminders that the planet's journey through space is fraught with danger. Professor Iain Stewart explores what meteorites and asteroids are, where they come from, the risks they pose and the role they have played in Earth's history