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An illustration of DART approaching its target asteroid system. |Image credit: NASA/Johns Hopkins APL/Steve Gribben
In 2022, NASA’s Double Asteroid Redirect Test (DART) mission deliberately struck the asteroid Dimorphos, which orbited a larger asteroid called Didymos. Now, scientists have confirmed that DART not only changed Dimorphos’ orbit around its binary companion, but also changed the orbit of the entire binary system around the sun.
“The change in orbital velocity of the binary system is about 11.7 micrometers per second, or 1.7 inches per hour,” Rahil Makadia of the University of Illinois at Urbana-Champaign said in a report. statement. “Such small changes in an asteroid’s motion over time could cause dangerous objects to hit or miss our planet.”
goal dart The goal was to see if a kinetic impactor, in this case the DART spacecraft, could asteroid and prove that if an asteroid of similar size is Earthwe can exclude it.
this Didymus-Demophos The binary asteroid system is a safe place to practice. Didymos is the larger asteroid, about 2,788 feet (850 meters) in diameter, and the smaller asteroid Dimorphos, 560 feet (170 meters) in diameter, orbits Didymos. Since astronomers had previously accurately measured Demovos’ orbital period and radius, any deflection caused by the impact could also be clearly measured. Additionally, because Dimorphos is gravitationally connected to Didymos, a DART impact would not inadvertently knock it toward Earth.
The DART impact occurred on September 26, 2022, with the spacecraft impact speed of 4 miles (6.6 kilometers) per second. It impacted Dimorphos enough to shorten its orbital period around Didymos from 11 hours and 55 minutes to 11 hours and 23 minutes. Before impact, the goal was to nudge Dimorphos to shorten its orbital period by at least 73 seconds, meaning the mission was a resounding success.
New data analysis led by Marcadia and Steve Chesley of NASA’s Jet Propulsion Laboratory (JPL) shows that DART’s efforts to propel Dimorphos were aided by a cloud of debris, called ejecta, that is ejected into space while digging a new crater.
As this jet cloud flies away from Demovers, it takes momentum with it. And, since momentum is always conserved, this gives Dimorphos an extra boost. Scientists call this extra thrust the “momentum enhancement factor,” which in the case of the Dimorphos and DART impacts was 2. This means that the loss of ejecta doubled the thrust exerted on Dimorphos by the initial DART impact.
The Italian Space Agency’s LICIA CubeSat mission, flying with DART, captured the impact and ejection of the ejecta cloud from Dimorphos. |Image source: ASI/NASA
Because Dimorphos and Didymos are connected by an invisible bond gravitythis extra thrust pushed Dimorphos and Didymos away from their surrounding sunchanging its orbital period by 0.15 seconds.
That may not sound like much, but as Markadia mentioned, it’s enough to push dangerous asteroids away from Earth (as long as the asteroid is discovered in time).
To this end, NASA plans to launch a new space telescope called the Near-Earth Object (NEO) Surveyor sometime after September 2027. NEO surveyorIts mission will be to find as many of the remaining undiscovered asteroids close to Earth’s orbit as possible.
Determining the changes in Didymos and Dimorphos’ orbits around the Sun is a labor of love, especially for the 49 amateur astronomers who travel to both ends of the Earth in search of occultations.
A stellar occultation occurs when an object passes in front of a star from our perspective. When an asteroid obscures a star, we can learn about the asteroid’s shape, size, location, and trajectory.
Unfortunately, stellar occultations are difficult to observe—they can only be seen from randomly narrow orbits on the Earth’s surface. However, thanks to amateur astronomers who traveled around the world between October 2022 and March 2025 and witnessed 22 occultations of the Didymos-Dimorphos system, Makadia and Chesley’s team were able to calculate changes in the binary system’s orbit around the sun.
“When combined with years of existing ground-based observations, these stellar occultation observations became key in helping us calculate how DART altered Didymos’ orbit,” Chesley said. “This work is highly weather-dependent, often requires travel to remote locations, and success is not guaranteed. This result would not have been possible without the dedication of dozens of volunteer occultation observers around the world.”
Based on the orbital changes, the densities of the two asteroids can also be calculated. Didymos has a density of 2,600 kilograms per cubic meter, while Dimorphos has a lower density than expected, at 1,540 kilograms per cubic meter, making it somewhat like a loose pile of rubble. This supports the hypothesis that Dimorphos were formed from materials that were once derived from Didymos.
These latest findings from the DART mission were published March 6 in the journal scientific progress.
