The US National Aeronautics and Space Administration (Nasa) has reported that its Double Asteroid Redirection Test (DART) spacecraft had successfully impacted its target, the asteroid moonlet Dimorphos. DART is an Earth defence experiment, aimed at proving a means of protecting our planet from hazardous asteroids. That means involves using the impact of a spacecraft to alter the trajectory of such an asteroid.

Dimorphos has a diameter of some 160 m, and orbits a larger asteroid, the 760-m-diameter Didymos. Neither asteroid poses a threat to Earth.

“At its core, DART represents an unprecedented success for planetary defence, but it is also a mission of unity with a real benefit for all humanity,” highlighted Nasa administrator Bill Nelson. “As Nasa studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”

DART was a 570-kg box-shaped spacecraft, equipped with just one instrument, the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO). This helped DART’s sophisticated guidance, navigation and control system (that worked with Small-body Manoeuvring Autonomous Real Time Navigation algorithms) to identify both asteroids and target the smaller one. DART also carried, and launched, the Italian Space Agency’s Light Italian CubeSat for the Imaging of Asteroids (LICIACube).

DRACO took images of Dimorphos up until seconds before impact. LICIACube imaged the impact and the resultant cloud of matter ejected from the asteroid. As the CubeSat has only a small antenna, it will take some weeks to download all its images, one at a time. DART hit the moonlet at a velocity of about 22 530 km/h.

It will also take time to determine the actual effect of DART’s impact on Dimorphos. The objective was to shorten Dimorphos’ orbit around Didymos by some 1%, or ten minutes. The two asteroids, which are about 11 million kilometres from Earth, are being observed by dozens of telescopes around the world.

“DART’s success provides a significant addition to the essential toolbox we must have to protect Earth from a devastating impact by an asteroid,” affirmed Nasa Planetary Defence officer Lindley Johnson. “This demonstrates we are no longer powerless to prevent this type of natural disaster. Coupled with enhanced capabilities to accelerate finding the remaining hazardous asteroid population by our next Planetary Defence mission, the Near-Earth Object Surveyor, a DART successor could provide what we need to save the day.”