up to 20 metres wide. but this should also give the rock a kick which will speed up its orbit. and this can be monitored from the earth to see if it's worked. all you really need is a nudge, because the distances you're going and the speeds you're going, a tiny change in direction can result in a huge change in how far it's going to miss the earth. and that could be vital. a 160 metre wide rock like diomorphos could be catastrophic for populated areas. bigger asteroids that are kilometres across have the potential to devastate the planet. the hope is this mission will show us if it's possible to stop future collisions. the spacecraft will arrive at its destination next autumn. rebecca morelle, bbc news. without wishing to scare you at all! all you need is a little nudge to push the asteroid, we will be fine. we will see live pictures of the rocket taking off in about ten minutes, hopefully. they are saying