DART impact mission shows we could deflect Earth-bound asteroid

The asteroid-deflecting DART mission worked with incredible accuracy.

By Lewis Dartnell

Published: Tuesday, 18 April 2023 at 12:00 am

Although no known asteroid poses a threat to Earth for at least the next century, the database of near-Earth asteroids is not yet complete for smaller bodies that could still cause devastation on a regional scale.

Several methods have been proposed to protect Earth from asteroids on a collision course, including blowing them up with a nuclear weapon and using a ‘gravity tractor’, a large spacecraft whose gravity pulls the asteroid so it misses our planet.

The strategy identified as the highest priority to develop and test, however, is kinetic impact.

In simple terms: fly a spacecraft at high speed into the asteroid so that it is nudged onto a different trajectory.

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Asteroid moonlet Dimorphos as seen by the DART spacecraft, 11 seconds before impact. Credit: NASA/Johns Hopkins APL

NASA’s DART (Double Asteroid Redirection Test) mission was developed to demonstrate just this approach.

Launched in November 2021, DART successfully impacted Dimorphos, the 160m moon of 800m asteroid Didymos, at just over 22,000km/h at 23:14 UTC on 26 September 2022.

A number of research papers have described what this milestone space mission taught us.

Here I’m focusing on a report led by Terik Daly, Carolyn Ernst and Olivier Barnouin, all at Johns Hopkins University Applied Physics Laboratory, which pieces together the details of the impact itself with astonishing precision.

DART continuously beamed back images from its onboard camera during the approach.

The final full image, taken just under two seconds before impact, shows a boulder-strewn landscape, with a pixel resolution of just 5cm.

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The last complete image of asteroid moonlet Dimorphos, captured by the DRACO imager on NASA’s DART mission, about 12km from the asteroid and 2 seconds before impact. Credits: NASA/Johns Hopkins APL

DART impacted in the direction opposite the asteroid’s motion, almost straight down into the asteroid’s surface, at an angle of around 73°.

By analysing the images, the team determined the precise point that DART hit to an accuracy of better than 70cm.

The impact site was within 25m of the equator of Dimorphos: like striking a snooker ball with the cue, the perfect spot to hit to impart the maximum momentum (without ‘wasting’ any of the impact energy in causing the target body to spin).