Milky Way

"DART would be NASA's first mission to demonstrate what's known as the kinetic impactor technique - striking the asteroid to shift its orbit - to defend against a potential future asteroid impact," said Lindley Johnson, planetary defence officer at NASA Headquarters in Washington.

DART, scheduled for launch in 2020, would impact only the smaller of the two bodies, Didymos B.

The spacecraft would strike the smaller body at a speed about nine times faster than a bullet, approximately six kilometres per second.

The kinetic impact technique works by changing the speed of a threatening asteroid by a small fraction of its total velocity, but by doing it well before the predicted impact so that this small nudge will add up over time to a big shift of the asteroid's path away from Earth.

"DART is a critical step in demonstrating we can protect our planet from a future asteroid impact," said Andy Cheng of The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, the DART investigation co-lead.