Spaceship crash reshaped asteroid orbit, structure

What happens when you take a spaceship worth hundreds of millions of dollars, blast it into space and deliberately smash it into an asteroid at speeds of 23,000km/h?

Well, as confirmed by NASA last year, you’ll probably take a hefty chunk out of the asteroid.

Thanks to the Double Asteroid Redirection Test (DART) mission, the US space agency was able to successfully demonstrate a well-aimed object could knock an asteroid off course.  Dimorphos, the mission’s target 160m wide asteroid orbits a larger ‘parent’ dubbed Didymos.

By targeting the smaller of the pair, NASA wanted to see whether a big enough impact could shift the trajectory of an asteroid as a test case for developing planetary defences.

NASA, through its Jet Propulsion Laboratory and partner universities, developed the DART project to have a ‘dry run’ at a planetary defence system.

But it wasn’t just Dimorphos’ orbit that appears to have changed.

“When DART made impact, things got very interesting,” says JPL navigation engineer Shantanu Naidu.

Dimorphos was found to be a ‘rubble pile’ asteroid – an accumulation of space rocks and dust like the asteroid Bennu – and imagery of the impact taken by orbiting cubesats showed a plume of debris ejecting from the moonlet after DART smashed into it.

A study led by Naidu and published in The Planetary Science Journal found the aftermath of the impact left Dimorphos looking a little worse for wear. Having previously been a potato-shaped ‘oblate spheroid’ it’s now described by Naidu as “a ‘triaxial ellipsoid’ – something more like an oblong watermelon”.

Modelling asteroids

Combining pre-impact images taken by DART’s on-board camera with radar pings from NASA’s Deep Space Network radars and ground-based telescopes observing the passage of reflected sunlight from the two objects, NASA’s teams were able to quickly determine Dimorphos’ orbit was about 33 minutes shorter after the DART collision.

The slight dimming of light seen by telescopes as one of the asteroids passes in front of the other enables researchers to make very precise calculations about the nature of the two objects.

“Before impact, the times of the events occurred regularly, showing a circular orbit [of Dimorphos],” says JPL senior research scientist Steve Chesley.

“After impact, there were very slight timing differences, showing something was askew. We never expected to get this kind of accuracy.”

It means that, just as its shape has been elongated by the impact, Dimorphos now also has a wobbly, stretched orbital path around Didymos.

But the best evidence of the DART impact is yet to come. The European Space Agency is due to launch a survey mission in October to inspect the aftermath of the collision. Named ‘Hera’, this project will be conducting a more civilised reconnaissance of the two asteroids – with no scheduled collisions – when it arrives in December 2026.

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