The mission is Nasa’s first demonstration of the agency’s planetary-defence initiative to protect Earth from the possibility of a hazardous collision with an asteroid. This particular asteroid, called Dimorphos, is not headed towards our planet but was singled out by Nasa to test a deflection technique. If measurements show the asteroid’s course was even slightly altered, Nasa will deem the mission a success.

 

It will take days or weeks before astronomers know if DART’s impact did its job, but a camera on-board the spacecraft captured a close-up view of the asteroid moments before the crash. Dimorphos filled the entire frame of DART’s camera, showing boulders and intricate detail just as Nasa lost the spacecraft’s signal.

 

A separate spacecraft, deployed from DART before impact, also captured images of the collision, and Nasa has said it will share those images in coming days. Various telescopes, including the Hubble Space Telescope and the James Webb Space Telescope, also observed the impact.

 

The DART mission said they made almost a direct bullseye on Dimorphos, hitting the asteroid just 17m from its centre. “We’ll get a much better understanding of where we are from the impact images that the investigation team now is going to analyse for quite some time,” Elena Adams, the DART mission systems engineer at Johns Hopkins, said during a press conference after the impact.

 

If in the future a hazardous asteroid is spotted heading towards Earth, it is possible that Nasa or some other space agency could send a spacecraft to ram it just as DART has done. Such an impact could impart just enough momentum to slightly change the asteroid’s trajectory so that, over time, it whizzes safely by Earth.

 

Dimorphos is actually an asteroid moonlet, orbiting around a much larger asteroid named Didymos. 

 

Now that DART has rammed into Dimorphos, astronomers on Earth will observe the asteroid system with optical and radar telescopes over the coming weeks to see how the spacecraft changed the asteroid’s orbit around Didymos. Just before impact, Dimorphos’s orbit around Didymos was just under 12 hours. NASA anticipates that DART’s collision could change the orbit by several minutes.

 

Nasa picked Dimorphos as a target because of its size. Measuring 160m across, it represents the kinds of asteroid that Nasa and other space agencies are most worried about. Astronomers have catalogued most of the giant asteroids that would destroy our planet, and none identified pose a risk for the foreseeable future. But astronomers believe they have found less than half of the many thousands of asteroids similar in size to Dimorphos that are flying near Earth. Were one of these rocks to crash into the planet, it could cause devastation.

 

“This would be regionally devastating over a populated area, a city, a state, or a country,” said Nancy Chabot, the co-ordination lead for DART at the Johns Hopkins Applied Physics Laboratory. “So you might not be talking global extinction, but you still want to be able to prevent this if you could.”

 

But such a scenario could be remedied in the future with the DART technique. The collision seemed to go just as Nasa expected, with no glitches along the way.

 

“Our first planetary defence test was a success and I think we can clap to that,”  Adams said to applause. “I think that earthlings should sleep better. Definitely, I will.”