NASA’s DART mission proved that a spacecraft can nudge an asteroid system in space, offering a real test of planetary defense.
NASA’s DART (Double Asteroid Redirection Test) spacecraft changed the motion of an asteroid system in space, demonstrating that a kinetic impactor could be a viable way to deflect a near-Earth object if one ever threatened Earth.
New findings show that when the spacecraft deliberately crashed into the asteroid moonlet Dimorphos in September 2022, the impact did more than alter the small body’s motion around its larger companion, Didymos. The collision also slightly changed the path that both asteroids follow around the Sun. Didymos and Dimorphos are gravitationally bound and circle a shared center of mass, forming what astronomers call a binary asteroid system. Because the two bodies are linked in this way, changing one affects the other.
First Measurable Human Impact on a Solar Orbit
According to a study published in the journal Science Advances, scientists carefully tracked the motion of the asteroid pair after the collision. They discovered that the system’s 770-day orbit around the Sun shifted by a fraction of a second following the DART impact.
This marks the first time that a spacecraft built by humans has measurably changed the solar orbit of a natural object.
“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 Collision Amplified the Push
When DART struck Dimorphos, the impact blasted a massive cloud of rock and dust into space and altered the shape of the asteroid, which is about 560 feet (170 meters) wide. The material that was thrown off the surface carried momentum away from the asteroid, producing an extra push. Scientists describe this effect as the momentum enhancement factor.
The more debris that escapes the asteroid, the stronger the push created by the collision. Researchers determined that the momentum enhancement factor for the DART event was about two. This means the debris roughly doubled the force delivered by the spacecraft itself.
Previous studies had already shown that the smaller asteroid’s orbit around Didymos, which is nearly half a mile wide (805 meters), became shorter after the collision. Dimorphos originally took about 12 hours to circle Didymos, but the impact shortened that period by 33 minutes.
The new analysis reveals that the event also expelled enough material from the binary system to slightly change its orbit around the Sun 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 for Planetary Defense
Didymos itself was never on a collision path with Earth, and the DART mission could not have placed it on one. However, the small shift in orbital speed illustrates how spacecraft impacts might one day be used to protect Earth if a dangerous asteroid is discovered heading our way. The key requirement would be spotting the object early enough to send a kinetic impactor mission.
NASA is preparing for that challenge by developing the Near-Earth Object (NEO) Surveyor mission. Managed by NASA’s Jet Propulsion Laboratory in Southern California, this new space telescope will be the first observatory designed specifically 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.
How Scientists Measured the Orbital Change
To confirm that the DART collision affected the entire asteroid system and not just Dimorphos, researchers needed extremely precise measurements of Didymos’ motion around the Sun. In addition to radar and other ground-based observations, they monitored stellar occultations.
A stellar occultation occurs when an asteroid passes directly in front of a star from our perspective, briefly blocking the star’s light. The momentary disappearance of the star allows scientists to calculate the asteroid’s position, speed, and shape with remarkable precision.
Capturing these events is difficult. Observers must be located in exactly the right places along the predicted path of the asteroid’s shadow as it crosses Earth. Multiple observing stations, sometimes miles apart, are required to gather enough data.
The research team relied on volunteer astronomers worldwide 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 changes in Didymos’ motion also allowed researchers to estimate the densities of both asteroids. Their calculations suggest that Dimorphos is slightly less dense than earlier estimates indicated.
This supports the idea that Dimorphos formed from debris shed by a rapidly spinning Didymos. Over time, the loose material gathered together under gravity, forming what scientists describe as a “rubble pile” asteroid.
Humanity’s First Mission 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 ongoing efforts to protect Earth from potential asteroid hazards.
The mission marked the first time humans intentionally changed the motion of a natural object in space, demonstrating a practical strategy that could one day help defend our planet from dangerous asteroids.
Reference: “Direct detection of an asteroid’s heliocentric deflection: The Didymos system after DART” by Rahil Makadia, Steven R. Chesley, David Herald, Davide Farnocchia, Nancy L. Chabot, Shantanu P. Naidu, Andrew S. Rivkin, Alexandros Siakas, Damya Souami, Paolo Tanga, Sotirios Tsavdaridis, Kleomenis Tsiganis, Sébastien Bouquillon and Siegfried Eggl, 6 March 2026, Science Advances.
DOI: 10.1126/sciadv.aea4259
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