When faced with the threat of an asteroid on a collision course with Earth, the immediate solution appears to be straightforward: a spacecraft can be directed to collide with the asteroid to alter its trajectory. This method was successfully demonstrated by NASA’s DART mission in 2022, which effectively changed the orbit of the asteroid Dimorphos. However, new research from the University of Illinois introduces a troubling perspective on asteroid deflection, indicating that incorrect targeting could merely postpone a potential impact.
Scientists have found that poorly executed asteroid deflection attempts could unintentionally guide these celestial bodies into regions of space known as “gravitational keyholes.” These areas are critical because they can modify an asteroid’s orbit, setting it on a collision course with Earth at a later date. This phenomenon can be likened to a game of pinball, where hitting the wrong bumper can send the ball back toward the flippers instead of away.
Rahil Makadia, a researcher at NASA, emphasized the importance of precision in asteroid deflection efforts. “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.
Developing Probability Maps for Safer Deflection
To address these risks, Makadia and his team have created “probability maps” that highlight the safest points for striking an asteroid. Each location on an asteroid’s surface has varying probabilities of leading to a gravitational keyhole after being deflected by a kinetic impactor. Constructing these maps involves a comprehensive understanding of the asteroid’s characteristics, including its shape, surface features, rotation, and mass. Ideally, a dedicated space mission would gather high-resolution images and data, allowing for precise mapping.
In cases where an asteroid is detected too late for a detailed mission, scientists can generate preliminary maps using ground-based telescope observations. The team has already produced probability maps for well-studied asteroids like Bennu, indicating optimal impact zones marked by crosshairs. These maps take into account the uncertainties inherent in space missions, acknowledging that even the most accurately aimed spacecraft may miss their target by several meters.
While the target for the DART mission was selected because the Didymos system is too massive to be deflected onto a collision course with Earth, future threats may not be so accommodating. Effective planetary defense missions will require meticulous planning and execution.
Future Missions and the Importance of Precision
The upcoming Hera mission, organized by the European Space Agency, is scheduled to reach the DART impact site in December 2026. This mission aims to gather valuable data that could enhance deflection strategies.
Currently, humanity has been fortunate, with no significant threats detected on a direct trajectory toward Earth. However, as astronomers continue to scan the skies, it is inevitable that one day an asteroid could be discovered with a direct path towards our planet. Thanks to the research led by Makadia and his colleagues, when the need arises for active planetary defense, we will possess the knowledge to aim accurately and effectively.
This research highlights the complexities involved in asteroid deflection and the critical need for precision in space missions. The ongoing work in developing probability maps is a promising step toward ensuring that when a potential impact threat arises, we are prepared to respond with the best possible strategy.
