A spacecraft has launched on a mission to test technology that could one day tip a dangerous asteroid off course. Nasa's Dart mission wants to see how difficult it would be to stop a huge space rock from colliding with Earth. The spacecraft will crash into an object called Dimorphos to see how much its speed and path can be altered.

If a chunk of cosmic debris measuring a few hundred metres across were to collide with our planet, it could unleash continent-wide devastation. A Falcon 9 rocket carrying the Dart spacecraft blasted off at 06:20 GMT on Wednesday from Vandenberg Space Force Base in California...

BBC: Nasa Dart asteroid spacecraft