NASA’s DART Mission Changed Orbit of Asteroid Didymos Around Sun
New research reveals that when NASA’s Double Asteroid Redirection Test (DART) spacecraft intentionally collided with the lunar asteroid Dimorphos in September 2022, it not only altered Dimorphos’ motion around its larger companion, Didymos; the crash also changed the orbit of the two asteroids around the Sun. Connected together by gravity, Didymos and Dimorphos orbit a common center of mass in a configuration known as a binary system, so changes to one asteroid affect the other.
As detailed in a study published Friday in the journal Science Advances, observations of the pair’s motion revealed that the 770-day orbital period around the Sun changed by a fraction of a second after the DART spacecraft impacted Dimorphos. This change marks the first time that a man-made object has measurably altered the path of a celestial body around the Sun.
“It’s a small change in the orbit, but given enough time, even a small change can turn into a significant deviation,” said Thomas Statler, senior scientist for small solar system bodies at NASA Headquarters in Washington. “The team’s incredibly precise measurement once again validates kinetic impact as a technique to defend Earth against asteroid dangers and shows how a binary asteroid could be deflected by impacting just one member of the pair.”
When DART hit Dimorphos, the impact threw a massive cloud of rocky debris into space, changing the shape of the asteroid, which is 170 meters wide. Because the debris pushed the asteroid away from its own momentum, it gave Dimorphos an explosive boost – what scientists call the momentum enhancement factor. More debris expelled means more punch. According to the new research, the momentum enhancement factor for DART’s impact was about two, meaning the loss of debris doubled the punch created by the spacecraft alone.
Previous research showed that the 12-hour orbital period of the smaller asteroid around Didymos, nearly half a mile wide (805 meters wide), was shortened by 33 minutes. The new study shows that the impact ejected so much material from the binary system that it also changed the binary system’s orbital period around the Sun by 0.15 seconds.
“The change in the orbital velocity of the binary system was about 11.7 microns per second, or 1.7 inches per hour,” said Rahil Makadia, lead author of the study at the University of Illinois at Urbana-Champaign. “Over time, such a small change in an asteroid’s motion can mean the difference between a dangerous object hitting or missing our planet.”
Although Didymos was not on an impact trajectory with Earth and it was impossible for the DART mission to put it on such a trajectory, this change in orbital velocity highlights the role that spacecraft – that is, kinetic impactors in this context – could play if a potentially dangerous asteroid were on a collision course in the future. The key is to detect near-Earth objects in sufficient time to deliver a kinetic impactor.
To this end, NASA is building the Near-Earth Object (NEO) Surveyor mission. Managed by NASA’s Jet Propulsion Laboratory in Southern California, this next-generation space survey telescope is the first to be built for planetary defense. The mission will search for some of the hardest-to-find near-Earth objects, such as dark asteroids and comets that don’t reflect much visible light.
To prove that DART had a detectable influence on both asteroids – and not just the smaller Dimorphos – researchers needed to measure Didymos’ orbit around the Sun with 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 point of light to go out for a fraction of a second. This technique provides extremely precise measurements of the asteroid’s speed, shape and position.
Measuring stellar occultations is a challenge: astronomers must be in the right place, at the right time, with multiple observing stations, sometimes several kilometers apart, to track the asteroid’s predicted path past a specific star. The team relied on volunteer astronomers from around the world who recorded 22 stellar occultations between October 2022 and March 2025.
“Combined with years of ground-based observations, these stellar occultation observations became essential in helping us calculate how DART had changed Didymos’ orbit,” said Steve Chesley, study co-leader and principal research scientist at JPL. “This work is highly dependent on weather conditions and often requires travel to remote areas 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 researchers calculate the densities of the two asteroids. Dimorphos is slightly less dense than previously thought, supporting the theory that it formed from rocky debris shed by a rapidly rotating Didymos. These loose materials eventually came together to form Dimorphos, a “rubble pile” asteroid.
The DART spacecraft was designed, built and operated by the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, for NASA’s Planetary Defense Coordination Office, which oversees the agency’s ongoing planetary defense efforts. It was humanity’s first mission to intentionally move a celestial object.
For more information on the DART mission, visit:
https://science.nasa.gov/mission/dart/
Media contacts
Ian J. O’Neill
Jet Propulsion Laboratory, Pasadena, California.
818-354-2649
ian.j.oneill@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
240-285-5155 / 240-419-1732
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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