Finding safe impact zones to deflect hazardous asteroids

Finding safe impact zones to deflect hazardous asteroids
by Erica Marchand
Paris, France (SPX) Sep 11, 2025

Selecting the point of impact for a kinetic deflection mission is not trivial, according to research unveiled at the EPSC-DPS2025 Joint Meeting in Helsinki. Striking the wrong location could nudge a hazardous asteroid through a gravitational keyhole and set up a future Earth encounter.

"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.

NASA proved kinetic impact can alter an asteroid's path when DART hit Dimorphos, the small moon of Didymos, in September 2022. DART acted as a high-speed projectile to change Dimorphos's orbit, demonstrating deflection. ESA's Hera mission will arrive at Didymos and Dimorphos in December 2026 to characterize the aftermath.

Because the Didymos system is too massive to be redirected toward Earth, DART's exact impact point mattered less. For other Sun-orbiting objects that pose risk, even small orbital tweaks could route them through a keyhole, a narrow region where a planet's gravity reshapes a flyby into a later collision course.

"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," said Makadia. Avoiding those zones requires mapping how surface strike locations translate into post-impact trajectories and their associated probabilities.

Makadia's team has devised a method to compute probability maps across an asteroid's surface, guided by DART results but tailored to each target. Inputs include the body's shape, topography, rotation and mass. Ideally a rendezvous mission provides these data, but timelines may preclude that for newly found threats.

"Fortunately, this entire analysis, at least at a preliminary level, is possible using ground-based observations alone, although a rendezvous mission is preferred," said Makadia. By propagating paths from many candidate impact points and flagging those that intersect keyholes, planners can identify safer strike zones.

"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," said Makadia. The approach offers a practical framework to select impact sites that deflect danger without unintentionally scheduling a future impact.