The Asteroid that Killed the Martian Magnetic Field

Click to viewOne of the many mysteries of Mars is how the planet lost its magnetic field 4 billion years ago. Evidence suggests the planet once had a magnetic field just like Earth's, created by a churning molten dynamo in the planetary core. But what could have caused that core to stop spinning, and stop generating a… » 7/20/08 2:00pm 7/20/08 2:00pm