Science journalist Dr. Robin George Andrews has provided his perspective on asteroid 2024 YR4 and the challenges associated with attempting to ‘use a DART-like spacecraft to alter its trajectory’.
Dr. Andrews addressed this topic on Twitter in a thread, responding to claims about NASA’s Double Asteroid Redirection Test (DART) spacecraft.
“DART was the first-ever mission dedicated to investigating and demonstrating one method of asteroid deflection by changing an asteroid’s motion in space through kinetic impact,” NASA states.
In September 2022, NASA’s DART spacecraft successfully collided with the asteroid Dimorphos, altering its orbit. This marked a historic achievement as it was ‘humanity’s first time purposely changing the motion of a celestial object and the first full-scale demonstration of asteroid deflection technology’.
So, why might it not be feasible to use a similar approach to prevent asteroid 2024 YR4 from impacting Earth? In his Twitter thread, Dr. Andrews points out that even though DART was successful, it ‘doesn’t mean we can use kinetic impactors like it to deflect any asteroid whenever we want, and that’s for several reasons,’ with the primary reason being that asteroids such as Dimorphos ‘and smaller, tend to be rubble piles’ rather than ‘solid single rocks’.
Asteroids, which can be described as ‘boulders weakly bound by their own gravity,’ risk being shattered if impacted ‘too hard’.
In the case of DART, Dimorphos was impacted ‘just right’, resulting in a ‘debris-like thrust effect’. However, if an asteroid were ‘disrupted’ and shattered, the resulting fragments could ‘still head for Earth’.
“This is chaotic, potentially very destructive—and if DART hit Dimorphos a little harder, it would have broken that asteroid too. You have to be very sure that when you hit an Earthbound asteroid, you are deflecting it, not fragmenting it,” Dr. Andrews remarks.
The second consideration? Although DART managed to reduce Dimorphos’ orbit by a significant 33 minutes, it didn’t actually ‘move’ it a great distance.
“The change in velocity delivered by the impact was 2.7mm/s,” Dr. Andrews continues.
What does this signify?
Dr. Andrews mentions he has heard it would require ’10 years or more to build, plan and execute an asteroid deflection mission’, and with asteroid 2024 YR4 potentially approaching Earth by 2032, the timeline is tight.
“This is because the deflection a kinetic impactor can give an Earthbound asteroid would be tiny. Only over time does the shifted orbit add up enough to ensure it’ll miss Earth,” he explains.
In the case of asteroid 2024 YR4, given its smaller size compared to Dimorphos—measuring 40-90 meters—it wouldn’t require as significant a deflection. However, there remains a considerable margin for error, especially considering that the next opportunity for detailed observations will be its Earth flyby in 2028.
Dr. Andrews poses the question: “If it’s too big, we may not be able to deflect it with one spacecraft. We’d need several to hit it perfectly, all without catastrophically breaking it. And with only a few years down the line, we could accidentally deflect it—but not enough to make it avoid the planet. Then, it still hits Earth, just somewhere else that wasn’t going to be hit.”
Fortunately, Dr. Andrews clarifies he’s ‘not saying a kinetic impactor mission, or missions, couldn’t work,’ but stresses ‘we don’t have much time’ and more data on the asteroid is crucial.
“Maybe 2024 YR4’s odds will rise, and we will successfully deflect it in 2028 using a monster-sized spacecraft. Or maybe we’ll break an awkward taboo and instead opt to use a nuclear warhead to try to deflect it, which would provide a bigger punch to the asteroid than DART,” he theorizes.
In conclusion, he suggests the asteroid ‘isn’t likely to be a problem at all’ and will ‘probably miss Earth’.
He concludes: “But if it doesn’t, we have to be wary of trying to save the world but accidentally making the problem worse. Maybe we’ll just have to get out of the asteroid’s way this time.”