When faced with an asteroid on a collision course with Earth, the immediate solution seems simple: divert it by impacting it with a spacecraft. This method was effectively demonstrated by NASA’s DART mission in 2022, which successfully altered the orbit of the asteroid Dimorphos. However, new research from the University of Illinois indicates that improperly aimed deflection attempts could lead to unintended consequences, potentially postponing the impact rather than preventing it.
Researchers have identified a phenomenon known as “gravitational keyholes,” which are specific areas in space where a planet’s gravity can alter the trajectory of an asteroid. If an asteroid is deflected into one of these keyholes, it may still collide with Earth, but at a later time, perhaps years or even decades down the line. The concept can be likened to a pinball machine where a misdirected shot sends the ball ricocheting back toward the flippers.
Rahil Makadia, a researcher at NASA, emphasized the importance of precision in 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 would face the same impact threat again down the line,” he stated.
To mitigate this risk, Makadia’s team has developed “probability maps” that pinpoint the safest locations to strike each asteroid. Each point on an asteroid’s surface presents varying probabilities of leading the asteroid into a gravitational keyhole following a kinetic impact. Creating these maps necessitates detailed knowledge of the asteroid’s attributes, including its shape, surface features, rotation, and mass. Ideally, this information would be gathered through a dedicated space mission that can capture high-resolution images and data.
In cases where an asteroid is detected late, scientists can still produce preliminary, lower-quality maps using ground-based telescope observations. The researchers have already generated probability maps for well-studied asteroids like Bennu, incorporating crosshairs that indicate optimal impact zones. These maps take into account the inherent uncertainties in space missions, as even the most precisely targeted spacecraft may miss its mark by several meters.
While the target for DART, Dimorphos, was chosen because the Didymos system is too massive to be deflected onto a collision course with Earth, future asteroid threats may not be as forgiving. Effective planetary defense missions 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 gather critical data that will refine these deflection techniques. So far, no significant threats have been identified heading directly toward Earth, but as astronomers continue to explore the cosmos, it is inevitable that one day they will discover an asteroid with the potential to impact our planet.
Thanks to the research led by Makadia and his team, future planetary defense efforts will be better equipped to accurately target asteroids, enhancing our chances of safeguarding Earth from potential collisions.
