A series of new studies analyzing NASA’s DART mission to derail an asteroid have confirmed that humanity potentially has a tool to protect our planet from a devastating impact.
On September 26, 2022, humanity changed the course of a celestial object for the first time in history by deliberately crashing a spacecraft into a small asteroid orbiting a larger space rock.
The purpose of this NASA mission, known as the Dual Asteroid Redirection Test (DART), was to inform an approach to protecting Earth from any potentially dangerous asteroids in the future (it is important to note that the risk of collision with an asteroid has not been known for at least a century).
Now scientists have announced that DART has shortened the period it takes for the moon Dimorphos to orbit its asteroid companion Didymos by as much as 33 minutes, according to five new studies, published in the journal Nature – the first results of this unprecedented collision are described in detail there.
Scientists predicted that the Dimorphos period would change by about 7 minutes if the spacecraft directly transferred its momentum to the asteroid, but soon after the collision, it became clear that the complex dynamics of the collision resulted in a more dramatic change in the trajectory of the asteroid.
“People may think of the DART mission as a fairly straightforward experiment that is similar to playing billiards in space—one solid spacecraft impacts into one solid asteroid,” said Cristina Thomas, a planetary scientist at Northern Arizona University, who led a study about Dimorphos’ orbital shift. “However, asteroids are far more complex than just a solid rock; in fact most asteroids are what we think of as rubble piles. If you hit a rubble pile with a spacecraft, a lot of material will be ejected and fly away.”
“For a perfectly inelastic collision—one solid spacecraft directly impacting the asteroid with no material ejected—the orbital period change was estimated to be seven minutes,” she added. “We calculated a period change of 33 minutes, which is much larger and shows how important that extra moment from the ejected material was to the orbit period change.”
In addition to the findings of Christina Thomas’ team, DART scientists presented new observations and conclusions about the collision in Nature. Taken together, these five studies provide important lessons about the potential of using a kinetic impactor like DART to redirect the trajectories of any asteroids that might be on a collision course with Earth.
Researchers led by Terik Daly, a planetary scientist at Johns Hopkins University Applied Physics Laboratory, performed a step-by-step reconstruction of DART’s approach, impact, and fall to Dimorphos and arrived at the conclusion that “the resulting change in Dimorphos’s orbit demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary”.
Jian-Yang Li, a senior scientist at the nonprofit Planetary Science Institute, led research on the Hubble Space Telescope’s observations of the crash, and its aftereffects, which provide “a framework for understanding the fundamental mechanisms acting on asteroids disrupted by natural impact,” says the study.
Scientists led by Andrew Cheng, chief scientist for the planetary defense at the Johns Hopkins Applied Physics Laboratory, reported on “the first determination of the momentum transferred to an asteroid by kinetic impact.”
Cheng’s team confirmed that the material ejected by the DART impact caused a recoil effect that caused a much larger change in Dimorphos’ orbit than the impact itself.
“That ejected material carries energy and, most importantly, momentum,” Christina Thomas explained. “The period change that we observe is not just the result of the momentum transfer from the impacting spacecraft, but also due to that extra momentum boost from the motion of the ejected material.”
Finally, scientists led by Ariel Graykowski, a postdoctoral fellow at the nonprofit SETI Institute, in their study report on optical observations of Dimorphosus before, during, and after the collision using a network of public science telescopes around the world. These observations show the colors and brightness of the collision and its aftermath over several weeks — data that will help inform any future missions to study the kinetic collision.
New research offers the first lessons from a mission that literally moved an astronomical object and created a roadmap for protecting Earth from asteroids that could threaten to destroy cities, countries, or even life on a planetary scale, like the rock that wiped out the dinosaurs about 66 million years ago.
To that end, scientists will continue to monitor new properties of Dimorphos, including its orbit and the long trail of debris left by the collision. These observations will be collected both from Earth and by future space missions, such as the European Space Agency’s Hera spacecraft, which is due to collect close-up images of asteroids as it orbits the system in the coming years.