In a landmark achievement for planetary defense, a NASA mission has successfully altered the orbit of an asteroid system, marking the first time humanity has measurably changed the motion of a celestial body. New data, published Friday in the journal Science Advances, reveals that the impact of the Double Asteroid Redirection Test (DART) not only shifted the smaller asteroid Dimorphos’ orbit, but also subtly altered the orbit of its larger companion, Didymos, around the sun.
The DART mission, intentionally colliding with Dimorphos in September 2022, was designed to test a potential method for deflecting asteroids that might one day pose a threat to Earth. Whereas neither Didymos nor Dimorphos present any current risk, the binary asteroid system provided an ideal, controlled environment for evaluating the effectiveness of a kinetic impactor. The recent findings confirm the mission’s success, demonstrating a viable technique for planetary protection.
The study details that the time it takes for Didymos and Dimorphos to complete one orbit around the sun has decreased by a fraction of a second – specifically, 0.15 seconds – following the DART impact. This seemingly minuscule change is significant, representing the first instance of a human-made object measurably influencing the path of a celestial body around our star. “The change in the binary system’s orbital speed was about 11.7 microns per second, or 1.7 inches per hour,” explained Dr. Rahil Makadia, a planetary defense scientist involved in the DART mission, in a statement. “Over time, such a small change in an asteroid’s motion can make the difference between a hazardous object hitting or missing our planet.”
Didymos and Dimorphos are what’s known as a binary asteroid system, meaning the smaller asteroid, Dimorphos, orbits the larger one, Didymos. NASA describes Didymos as shaped like a spinning top and composed of loosely bound dust and rock, a “rubble pile” asteroid. Dimorphos, also a rubble pile, likely formed from debris shed by Didymos. The DART impact released an estimated 35.3 million pounds (16 million kilograms) of debris, 30,000 times the spacecraft’s mass, with the force of the ejected material proving more impactful than the spacecraft itself.
Measuring the Impact: Stellar Occultations and Volunteer Astronomers
Determining the extent of the orbital changes required precise measurements, achieved through a combination of ground-based observations and a technique called stellar occultation. This involves observing the momentary dimming of starlight as an asteroid passes in front of it. The study relied on 22 stellar occultations observed between October 2022 and March 2025, a challenging process requiring precise timing and often necessitating travel to remote locations. “This work is highly weather dependent and often requires travel to remote regions with no guarantee of success,” said Steve Chesley, a senior research scientist at NASA’s Jet Propulsion Laboratory. “This result would not have been possible without the dedication of dozens of volunteer occultation observers around the world.”
Previous research had already shown that the DART impact reduced Dimorphos’ orbit around Didymos by 33 minutes. The new findings build on this, demonstrating a broader effect on the entire system’s orbital path around the sun.
What’s Next: The Hera Mission and Future Planetary Defense
Further insights into the DART mission’s effects are expected later this year with the arrival of the European Space Agency’s Hera mission. Launched in 2024, Hera will conduct a detailed flyby of the Didymos-Dimorphos system, capturing new images of Dimorphos and providing a more comprehensive assessment of the impact’s consequences.
Meanwhile, NASA is developing the Near-Earth Object Surveyor mission, designed to identify potentially hazardous asteroids that remain difficult to detect with current Earth-based observatories. These efforts underscore a growing commitment to planetary defense, recognizing that a kinetic impactor, like the one used in the DART mission, could be a crucial tool for safeguarding Earth from future asteroid threats.
“The team’s amazingly precise measurement again validates kinetic impact as a technique for defending Earth against asteroid hazards,” said Thomas Statler, lead scientist for solar system small bodies at NASA. “If an asteroid that poses risks to our world is found with enough time to deflect it, a kinetic impactor like DART could be sent to nudge the space rock, or its companion, into a more benign orbit that misses Earth.”
The success of the DART mission and the ongoing research into asteroid deflection represent a significant step forward in our ability to protect our planet from potential cosmic impacts. Continued observation and development of planetary defense technologies will be crucial as we strive to understand and mitigate the risks posed by near-Earth objects.
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