NASA’s DART (Double Asteroid Redirection Test) mission did more than alter the motion of a small asteroid. New research shows the spacecraft’s deliberate collision with the asteroid moonlet Dimorphos in September 2022 also slightly changed the path of the entire asteroid system around the Sun. The finding provides strong evidence that a kinetic impactor could be used as a planetary defense method to redirect a potentially hazardous near-Earth object.
Dimorphos and its larger partner Didymos are bound together by gravity. The two asteroids orbit a shared center of mass in what scientists call a binary system. Because they are gravitationally linked, any change to one of them can influence the motion of the other.
First Time Humans Altered a Solar Orbit
According to a study published in the journal Science Advances, scientists carefully tracked the movement of the asteroid pair after the impact. Their measurements showed that the system’s 770-day orbit around the Sun changed by a fraction of a second following the collision.
This marks the first time a human-made spacecraft has measurably changed the orbit of a natural object around the Sun.
“This is a tiny change to the orbit, but given enough time, even a tiny change can grow to a significant deflection,” said Thomas Statler, lead scientist for solar system small bodies at NASA Headquarters in Washington. “The team’s amazingly precise measurement again validates kinetic impact as a technique for defending Earth against asteroid hazards and shows how a binary asteroid might be deflected by impacting just one member of the pair.”
Debris From the Impact Amplified the Push
When the DART spacecraft struck Dimorphos, it blasted a massive plume of rocky debris into space and reshaped the asteroid, which is about 560 feet (170 meters) wide. The debris carried momentum away from the asteroid, effectively adding extra thrust to the impact. Scientists refer to this effect as the momentum enhancement factor.
The more material ejected from the surface, the stronger the push delivered to the asteroid. Researchers determined that the momentum enhancement factor from the DART impact was about two. In other words, the debris roughly doubled the force produced by the spacecraft alone.
Earlier studies had already shown that the collision shortened Dimorphos’ orbit around the larger asteroid Didymos, which measures nearly half a mile across (805 meters), by 33 minutes from its original 12-hour period.
The new research found that the impact also expelled enough material from the binary system to slightly alter its path around the Sun. Specifically, the system’s orbital period changed by about 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 Rahil Makadia, the study’s lead author 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.”
Why Small Orbital Changes Matter
Didymos itself was never on a path toward Earth, and the DART experiment could not have placed it on one. However, the small shift in orbital speed demonstrates how spacecraft could be used to redirect a threatening asteroid if scientists detect it early enough.
In that scenario, a spacecraft would strike the object and slightly alter its velocity. Over time, that tiny change could accumulate into a large enough deviation 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 specifically designed for planetary defense.
The telescope will search for difficult to detect near-Earth objects, including dark asteroids and comets that reflect very little visible light.
Tracking the Asteroids With Stellar Occultations
To confirm that the DART collision influenced both asteroids, researchers needed extremely precise measurements of Didymos’ orbit around the Sun. In addition to radar and other ground based observations, they relied on stellar occultations.
A stellar occultation occurs when an asteroid passes directly in front of a distant star, briefly blocking its light. Observing that momentary disappearance allows scientists to calculate the asteroid’s position, speed, and shape with remarkable precision.
Capturing these events can be difficult. Observers must be located in exactly the right positions along the predicted path where the asteroid will pass in front of the star. This often requires multiple observation stations spread miles apart.
Researchers depended on volunteer astronomers around the world 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 study co-lead Steve Chesley, a senior research scientist at JPL. “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.”
Clues About How Dimorphos Formed
Tracking the asteroids’ motion also helped scientists estimate the densities of both objects. The results suggest that Dimorphos is slightly less dense than previously believed.
This finding supports the idea that Dimorphos formed from debris shed by a rapidly spinning Didymos. Over time, the loose rocky material likely gathered together under gravity, creating what scientists call a “rubble pile” asteroid.
Humanity’s First Attempt to Move a Celestial Object
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. This office leads NASA’s work to protect Earth from potential asteroid threats.
The mission marked the first time humans intentionally changed the motion of a natural object in space, providing a real-world demonstration of a possible strategy to defend our planet from dangerous asteroids.