Planetary defense efforts have been gaining momentum since NASA‘s Double Asteroid Redirection Test (DART) mission struck its target in September 2022 — but the full scope of that impact is only now becoming clear.
Scientists have confirmed that the DART spacecraft did more than alter the orbit of Dimorphos around its companion asteroid Didymos. According to the report, the collision shifted the entire binary asteroid system’s orbit around the sun, with the orbital period changing by 0.15 seconds.
A Hit That Exceeded Expectations
The spacecraft struck Dimorphos on September 26, 2022, traveling at 4 miles (6.6 kilometers) per second. The goal had been modest: reduce the smaller asteroid’s orbital period around Didymos by a minimum of 73 seconds. The actual result was far beyond that target. The orbital period shortened from 11 hours and 55 minutes to 11 hours and 23 minutes — a reduction of 32 minutes.
A key factor in that outsized result was the cloud of debris the impact kicked up. As this ejecta sprayed away from Dimorphos, it carried momentum with it. Because momentum is always conserved, that loss gave the asteroid an additional push — effectively doubling the thrust from the initial strike. Scientists describe this multiplier as the “momentum enhancement factor,” which in this case had a value of two.
New analysis led by Rahil Makadia of the University of Illinois Urbana-Champaign and Steve Chesley of NASA’s Jet Propulsion Laboratory (JPL) quantified the sun-orbital shift precisely. “The change in the binary system’s orbital speed was about 11.7 microns per second, or 1.7 inches per hour,” Makadia said 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.”
Why the Target Site Was Chosen
Didymos measures approximately 2,788 feet (850 meters) across. The smaller Dimorphos, at 560 feet (170 meters), orbits around it. Astronomers had already measured Dimorphos‘s orbital period and radius precisely before the mission, making any deflection straightforward to detect. The gravitational bond between the two bodies also meant the impact carried no risk of redirecting Dimorphos toward Earth.
The Italian Space Agency’s LICIA cubesat, which flew alongside DART, captured both the moment of impact and the subsequent ejecta spray, providing direct visual confirmation of the event.
The finding carries a practical caveat: a small orbital nudge is only useful if a threatening asteroid is detected with enough lead time to act on it. To address that gap, NASA intends to launch the Near-Earth Object (NEO) Surveyor space telescope sometime after September 2027, with the specific mission of locating undiscovered asteroids near Earth’s orbital path.
Photo by Tara Winstead on Pexels
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