Asteroid deflection must avoid ‘gravitational keyholes,’ experts say
Scientists warn that deflecting a hazardous asteroid with a spacecraft must be done with extreme precision, as striking the wrong spot risks sending it through a “gravitational keyhole” that could set up a future collision with Earth, reports a Kazinform News Agency correspondent.
The warning was presented this week at the EPSC-DPS2025 Joint Meeting in Helsinki. Researchers are building on lessons from NASA’s Double Asteroid Redirection Test (DART) mission, which successfully demonstrated the principle of asteroid deflection in 2022.
“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. Otherwise, we'd be facing the same impact threat again down the line,” said Rahil Makadia, a NASA Space Technology Graduate Research Opportunity Fellow at the University of Illinois at Urbana-Champaign.
In September 2022, DART deliberately struck the small asteroid Dimorphos, which orbits the larger Didymos, proving that a kinetic impactor can alter an asteroid’s trajectory. While that system poses no risk to Earth, researchers note that for other objects orbiting the Sun, even a minor shift in orbit could lead to a dangerous outcome.
The so-called gravitational keyhole is a small region in space where a planet’s gravity can redirect an asteroid onto a return path, resulting in a later impact. “If an asteroid passed through one of these keyholes, its motion through the Solar System would steer it onto a path that causes it to hit Earth in the future,” Makadia explained.
To prevent such scenarios, scientists are developing probability maps to calculate the safest points on an asteroid’s surface to strike. Each location has different probabilities of pushing the object into a keyhole, depending on its shape, rotation, mass, and surface features.
“Fortunately, this entire analysis, at least at a preliminary level, is possible using ground-based observations alone, although a rendezvous mission is preferred,” Makadia said.
A follow-up mission, the European Space Agency’s Hera, will arrive at Didymos and Dimorphos in December 2026 to gather further data.
“With these probability maps, we can push asteroids away while preventing them from returning on an impact trajectory, protecting the Earth in the long run,” Makadia concluded.
Earlier, it was reported that Japan intends to participate in a European Space Agency mission to monitor an asteroid expected to make a close approach to Earth in 2029, a project regarded as an important step in preparing for possible future collisions with space objects.