NASA’s DART (Double Asteroid Redirection Test) mission did more than just change the motion of a small asteroid. A new study shows that the probe’s intentional collision with the asteroid moon Dimorphos in September 2022 also slightly altered the path of the entire asteroid system around the sun. This discovery provides strong evidence that kinetic impactors can be used as a planetary defense tool to reorient potentially dangerous near-Earth objects.
Dimorphos and his larger partner Didymos are held together by gravity. The two asteroids orbit a common center of mass, which scientists call a binary star system. They are linked by gravity, so changes to one can affect the movement of the other.
Humanity was the first to change the sun’s orbit
According to a study published in the journal scientific progressscientists carefully tracked the movement of the asteroid pair after the collision. Their measurements showed that the system’s 770-day orbit around the sun changed just a fraction of a second after the impact.
This is the first time that a man-made spacecraft has measurably altered the orbit of a natural object around the sun.
“This is a small change in the orbit, but given enough time, even small changes can grow into large deflections,” said Thomas Statler, chief scientist for small solar system bodies at NASA Headquarters in Washington. “The team’s astonishingly precise measurements re-examine kinetic shock as a technique for protecting Earth from asteroid hazards and show how binary asteroids can be deflected by impacting one of the pairs.”
Debris from the impact amplifies the propulsion force
When the DART spacecraft hit Dimorphos, huge pieces of rock were blown into space, changing the shape of the approximately 560-foot (170-meter) wide asteroid. The debris carried momentum away from the asteroid, effectively adding extra thrust to the impact. Scientists call this effect the momentum enhancer.
The more material ejected from the surface, the stronger the force transmitted to the asteroid. The researchers determined that DART’s impact momentum enhancement factor was approximately 2. In other words, the debris roughly doubled the forces generated by the spacecraft alone.
Initial studies had already shown that the impact shortened Dimorphos’ orbit around the larger asteroid Didymos, which is about half a mile (805 meters) in diameter, by 33 minutes from its original 12 hours.
The new study found that the collision also ejected enough material from the binary system to slightly change its orbit around the sun. Specifically, the orbital period of this system changed by about 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 the study’s lead author Rahil McAdia of the University of Illinois at Urbana-Champaign. “Over time, small changes like this in an asteroid’s motion can make the difference between a dangerous object hitting Earth or not.”
Why small orbital changes are important
Didymos itself was never on a path to Earth, and DART’s experiments couldn’t place it on a path to Earth. But the small changes in orbital velocity indicate that if scientists can detect the threat early enough, they can use the spacecraft to redirect the threatening asteroid.
In that scenario, the spacecraft collides with an object, causing its velocity to change slightly. Over time, those small changes can accumulate into deviations large enough to prevent a collision with Earth.
To improve early detection of such threats, NASA is developing the Near Earth Object (NEO) Surveyor mission. Managed by NASA’s Jet Propulsion Laboratory in Southern California, the mission will deploy the first space telescope designed specifically for planetary defense.
The telescope will search for near-Earth objects that are difficult to detect, such as dim asteroids and comets that reflect little visible light.
Tracking asteroids through stellar occultation
To confirm that the DART impact affected both asteroids, the researchers needed to make very precise measurements of Didymos’ orbit around the sun. In addition to radar and other ground-based observations, they also relied on stellar occultations.
A stellar occultation occurs when an asteroid passes right in front of a distant star, temporarily blocking its light. By observing this instantaneous disappearance, scientists can calculate the asteroid’s position, velocity, and shape with incredible accuracy.
Capturing these events can be difficult. The observer must be placed at a precise location along the predicted path of the asteroid passing in front of the star. This often requires multiple observation points separated by several miles.
The researchers relied on volunteer astronomers around the world who recorded 22 stellar eclipses between October 2022 and March 2025.
“Combined with years of existing ground-based observations, these stellar occultation observations were key in calculating how DART changed Didymos’s orbit,” said study co-lead Steve Chesley, a JPL senior scientist. “This research is highly weather dependent and often requires travel to remote locations with no guarantee of success. This accomplishment would not have been possible without the dedicated cooperation of dozens of volunteer occult observers around the world.”
Clues about how Dimorphos was formed
Tracking the asteroid’s movement also helped scientists estimate the density of both objects. This result suggests that the density of Dimorphos is slightly lower than previously thought.
This discovery supports the idea that Dimorphos was formed from debris swept away by the rapidly rotating Didymos. Over time, loose rocky material likely came together under gravity, forming an asteroid that scientists call a “rubble heap.”
Humanity’s first attempt at celestial travel
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. The bureau leads NASA’s efforts to protect Earth from potential asteroid threats.
The mission was the first time humans have intentionally altered the behavior of natural objects in space and provided a real-world demonstration of a possible strategy to protect Earth from dangerous asteroids.
