An artwork of NASA’s DART mission, which was a kinetic impactor designed to test whether it is possible to deflect an asteroid /NASA. Scient...
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| An artwork of NASA’s DART mission, which was a kinetic impactor designed to test whether it is possible to deflect an asteroid /NASA. |
“Even if we intentionally push an asteroid away from Earth with a space mission, we must make sure it doesn’t drift into one of these keyholes afterwards,” said Rahil Makadia, a NASA Space Technology Graduate Research Fellow at the University of Illinois at Urbana-Champaign. “Otherwise, we’d be facing the same impact threat again down the line.”
Lessons from NASA’s DART Mission
NASA’s Double Asteroid Redirection Test (DART) successfully impacted the small asteroid Dimorphos, a moonlet of Didymos, in September 2022. The spacecraft, acting as a kinetic impactor, proved that nudging an asteroid into a slightly different orbit is possible. The upcoming ESA Hera mission, set to arrive in December 2026, will investigate the aftermath of DART’s strike in detail. While Didymos and Dimorphos posed no threat to Earth, other asteroids may present scenarios where a poorly aimed deflection could make things worse rather than better.
A gravitational keyhole is a narrow region in space that, if an asteroid passes through it, changes its orbital path in such a way that it collides with Earth on a future encounter. These “cosmic trapdoors” make asteroid deflection strategies complex. Hitting the asteroid in the wrong place risks nudging it directly into such a keyhole, postponing but not preventing disaster.
Makadia’s team has developed a method to create probability maps of an asteroid’s surface, showing which points are safer to target with a kinetic impactor. These maps incorporate data on an asteroid’s shape, rotation, surface features, and mass, helping identify impact zones that minimize the risk of deflection into a keyhole.
“With these probability maps, we can push asteroids away while preventing them from returning on an impact trajectory, protecting Earth in the long run,” Makadia explained. Ideally, a dedicated rendezvous mission would scout a hazardous asteroid before any deflection attempt, but time-sensitive threats may require reliance on ground-based observations alone. Rapid-response planning will be essential if humanity discovers an asteroid on a collision course with little warning.
As discoveries of near-Earth objects accelerate, the need for planetary defense strategies grows. DART showed that kinetic impactors work, but future missions must be guided with precision to avoid trading one risk for another. With international cooperation through planetary defense networks, scientists hope to refine these methods before the next real threat arrives.
