New measurements show that the DART impact in 2022 not only shortened the orbit of the moonlet Dimorphos around its parent asteroid, Didymos, but also subtly shifted the entire binary system’s path around the Sun.
This artist’s illustration shows the ejection of a cloud of debris after NASA’s DART spacecraft collided with the asteroid Dimorphos. Image credit: ESO / M. Kornmesser.
When NASA’s DART spacecraft struck Dimorphos, the impact blasted a huge cloud of rocky debris into space, altering the shape of the asteroid, which measures 170 m (560 feet) wide.
Because the debris carried its own momentum away from the asteroid, it gave Dimorphos an explosive thrust — what scientists call the momentum enhancement factor.
The momentum enhancement factor for DART’s impact was about two, meaning that the debris loss doubled the punch created by the spacecraft alone.
Earlier research showed that the moonlet’s 12-hour orbital period around the 805-m- (nearly 0.5-mile-) wide Didymos shortened by 33 minutes.
The new study shows the impact ejected so much material from the binary system that it also changed the binary’s 770-day orbital period around the Sun by 0.15 seconds.
“The change in the binary system’s orbital speed was about 11.7 microns per second, or 1.7 inches per hour,” said Dr. Rahil Makadia, a researcher at the University of Illinois Urbana-Champaign.
“Over time, such a small change in an asteroid’s motion can make the difference between a hazardous object hitting or missing our planet.”
To prove DART had a detectable influence on the binary system, the researchers needed to measure its orbit around the Sun to exquisite precision.
So, in addition to making radar and other ground-based observations of the asteroid, they tracked stellar occultations, which occur when the asteroid passes exactly in front of a star, causing the pinpoint of light to blink out for a fraction of a second.
This technique provides extremely precise measurements of the asteroid’s speed, shape, and position.
The authors relied on volunteer astronomers around the globe who recorded 22 stellar occultations between October 2022 and March 2025.
“When combined with years of existing ground-based observations, these stellar occultation observations became key in helping us calculate how DART had changed Didymos’ orbit,” said Dr. Steve Chesley, a researcher at NASA’s Jet Propulsion Laboratory.
“This work is highly weather dependent and often requires travel to remote regions with no guarantee of success.”
“This result would not have been possible without the dedication of dozens of volunteer occultation observers around the world.”
Studying changes in Didymos’ motion also helped the researchers calculate the densities of both asteroids.
Dimorphos is slightly less dense than previously thought, supporting the theory that it formed from rocky debris shed by a rapidly spinning Didymos.
This loose material eventually clumped together to form Dimorphos, a ‘rubble pile’ asteroid.
Our results demonstrate that targeting the secondary asteroid in binary systems constitutes a possible strategy for kinetic impact deflection, adding to humanity’s planetary defense capabilities.
“The DART mission was already a success story. An asteroid system that poses no threat to Earth was carefully selected and NASA crashed a spacecraft into the smaller moon, causing it to orbit its parent asteroid more quickly,” said Dr. Preeti Cowan, a researcher at the University of Auckland.
“This new analysis reveals an even more remarkable — and still safe — outcome.”
“The combined ‘kick’ from the impact of the spacecraft and the material blasted off the tiny asteroid moon was enough to measurably change the path of the binary system around the Sun.”
“The shift may seem small, but where orbits are concerned, even a tiny change applied early enough can have profound consequences.”
“This is an important milestone for planetary defense,” said Professor Roberto Armellin, a researcher at the University of Auckland.
“In a real hazard scenario, even a very small change applied early enough could cause a potentially dangerous asteroid to miss Earth.”
“The next step will come with ESA’s Hera mission, launched in 2024, which will visit the Didymos system later this year to measure the crater, the asteroid’s mass and structure, and the efficiency of the impact.”
“These measurements will help turn this historic experiment into a reliable planetary defense technique.”
The results appear in the journal Science Advances.
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Rahil Makadia et al. 2026. Direct detection of an asteroid’s heliocentric deflection: The Didymos system after DART. Science Advances 12 (10): 10.1126/sciadv.aea4259
