A theoretical mission to avert an asteroid heading straight for Earth is fraught with enough risk to write a Michael Bay film. Rather than the thrills of Armageddon, like a malfunctioning drill or a president with an itchy trigger finger, new research suggests one of the biggest risks facing an anti-asteroid operation would be a “gravitational keyhole” sending the rock looping back to Earth at a later date.
The work was highlighted at the Joint Meeting of the Europlanet Science Congress and the Division for Planetary Sciences (EPSC-DPS) in Helsinki.
"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 space technology researcher at the University of Illinois at Urbana-Champaign who presented the findings, in a press release.
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How DART Smashed an Asteroid
In 2022, fiction became reality when NASA organized a mission to intercept an asteroid. Their Double Asteroid Redirection Test (DART) smashed into the small asteroid Dimorphos, which orbits another asteroid called Didymos around 7 million miles from Earth. While neither asteroid was on a collision course with our world, the study was a success. It showed that an impact could successfully alter the path of a flying space rock, raising hopes that any Earth-bound objects could be sent on a new course by future missions.
Makadia’s new work suggests that in any Earth-threatening scenario, such redirection should consider the risk of slingshotting the rock into a so-called keyhole. This is a small area of space where a planet’s gravity tweaks the path of a passing asteroid in a way that causes it to return to the planet from a new angle years later. In this way, a DART-like mission that pokes an asteroid into a gravitational keyhole doesn’t avert danger, but only delays it.
The challenge for any future mission is to find a sweet spot on the side of an asteroid that sends it permanently into the void rather than on a return mission to Earth. Makadia’s team has developed a tool for predicting the path of a deflected asteroid, based on information processed from DART.
Finding the Perfect Strike Site
The technique incorporates a significant amount of information. The asteroid’s overall shape, mass, and rotation, along with topological details like craters or hills, are all factored into the analysis. While DART’s information is useful, as each potential asteroid threat will have its own unique structure, these details would ideally be gathered anew by a reconnaissance mission before redirection. If a rapidly approaching asteroid doesn’t give Earth the chance to check its contours with a spacecraft, Makadia said that analysis can be conducted from Earth’s surface.
The asteroid’s details can be processed to determine the likely trajectory of the asteroid after impact, allowing researchers to identify a perfect strike location.
"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," concluded Makadia in a press release.
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