A spacecraft built by Nasa is set to intentionally smash into a small asteroid as part of a planetary protection test mission, to help prove that this could be an effective way of deflecting dangerous incoming rocks.

The chosen asteroid, named Dimorphos, orbits Didymos in around 11 hours and 55 minutes, but Nasa astronomers hope that Dart will destroy itself and cut about 10 minutes off this time. The collision is expected to take place at about 6.8 million miles from Earth.  

"Dart's target asteroid is not a threat to Earth but is the perfect testing ground to see if this method of asteroid deflection - known as the kinetic impactor technique - would be a viable way to protect our planet if an asteroid on a collision course with Earth were discovered in the future," a Nasa spokesperson said. 

The mission has been designed to operate fully autonomously, to avoid putting human lives at risk. 

It will be the first full-scale demonstration...