Planetary defense has moved from theoretical modeling to measured, documented reality. The effect of NASA‘s 2022 DART mission — long confirmed as a success at the local scale — has now been quantified at the solar system level for the first time.
The Double Asteroid Redirection Test deliberately crashed a spacecraft into Dimorphos, a small asteroid orbiting a larger one called Didymos. The immediate result was well established: the impact shortened Dimorphos‘s orbital period around Didymos by 32 minutes. What had not been measured until now was whether that collision also altered the pair’s shared trajectory around the sun.
Using nearly 6,000 observations accumulated over the years since the impact, researchers calculated that the Didymos system has slowed by 11.7 micrometres per second — equivalent to roughly 40 millimetres per hour. According to the study, that deceleration is expected to reduce the radius of the system’s solar orbit by approximately 360 metres.
Small Numbers, Long Timelines
“It doesn’t sound like a lot, but the whole idea behind these kinetic impacts is that if you do one early enough, a small impact makes a large change in the overall position,” said Rahil Makadia of the University of Illinois Urbana-Champaign, part of the team monitoring the asteroids. “It’s a very tiny number, but if you let it accumulate over decades, then it can grow into a big one.”
The slowdown had two contributors: the physical force of the spacecraft’s collision and a secondary push generated by the plume of debris ejected from Dimorphos‘s surface on impact. The team found the two effects were roughly equal in magnitude. That breakdown allowed researchers to independently calculate the masses and densities of both asteroids — a byproduct of the analysis with its own scientific value.
Dimorphos turns out to be approximately half as dense as Didymos, lending support to the hypothesis that it is a rubble-pile body: a loosely aggregated structure formed from material shed by Didymos through rotational forces rather than a solid, cohesive rock.
A Reference Point for Future Missions
The practical significance of this data extends well beyond the Didymos system. “We now have one solid anchoring point to predict any future kinetic impact missions,” Makadia said. Before this work, planetary defense planning relied on models without empirical calibration at the orbital scale; the study, published in Science Advances, provides that anchor.
Further refinement is expected. The European Space Agency‘s Hera spacecraft is currently en route to Didymos and is scheduled to arrive in November. Its measurements are anticipated to deliver more precise data on the system’s properties, adding another layer of empirical grounding to future deflection planning.
Photo by Pixabay
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