Why did Nasa smash its spacecraft into an asteroid?

This week, Nasa scientists smashed a spacecraft into an asteroid,
more than 11m km from Earth. Most rocket scientists would wince at
the thought, but the Double Asteroid Redirection Test, or DART, was
purposefully designed to slam head-on into the asteroid Dimorphos.
The aim is to nudge it off its current orbit, in an experiment that
will assess the possibility of deflecting a killer space rock – if
one was ever headed our way. Ian Sample speaks to Prof Colin
Snodgrass about why they chose Dimorphos, what happens to the
asteroid now, and whether there are other ways to prevent
space-based planetary destruction. Help support our independent
journalism at theguardian.com/sciencepod