When an asteroid threatens Earth, deflecting it appears to be a straightforward solution. NASA’s successful demonstration of this concept through the DART mission in 2022, which altered the orbit of the asteroid Dimorphos, showcased the potential of kinetic impactors. However, recent findings from researchers at the University of Illinois suggest that poorly executed deflection attempts could inadvertently redirect asteroids towards Earth at a later date.
The study highlights a phenomenon known as “gravitational keyholes,” specific areas in space where an asteroid’s trajectory can be altered by a planet’s gravity. If an asteroid is deflected into one of these keyholes, it may still collide with Earth, just postponed by years or even decades. This scenario mirrors a pinball machine, where an errant strike can lead to unintended consequences.
Rahil Makadia, a researcher at NASA, emphasized the critical nature of precise asteroid deflection. “Even if we intentionally push an asteroid away from Earth with a space mission, we must ensure it doesn’t drift into one of these keyholes afterwards. Otherwise, we’d be facing the same impact threat again down the line,” he stated.
To mitigate this risk, Makadia and his team have developed “probability maps.” These maps pinpoint optimal impact locations on an asteroid’s surface, highlighting the safest spots for kinetic impactors to strike. Each surface point has a different probability of leading the asteroid into a gravitational keyhole post-deflection. Creating these maps requires comprehensive knowledge of an asteroid’s shape, surface features, rotation, and mass, ideally gathered through a dedicated space mission.
In cases where time is of the essence, scientists can generate preliminary maps using ground-based telescopes, although the quality may be lower. The researchers have already crafted probability maps for asteroids such as Bennu, illustrating the most effective impact zones with precise crosshairs.
While the DART mission targeted the Didymos system, which is too massive to be deflected towards Earth, future asteroid threats may not be so accommodating. Effective planetary defense will demand meticulous planning and execution. The European Space Agency’s upcoming Hera mission, scheduled to arrive at the DART impact site in December 2026, aims to refine these techniques by providing valuable data.
As of now, Earth has been fortunate, with no significant threats detected on a collision course. Yet, as astronomers continue to monitor the skies, the possibility remains that an asteroid could eventually pose a serious risk. Thanks to the work of Makadia and his team, preparedness for potential planetary defense scenarios is advancing, ensuring that when the time comes, the aim will be precise.
