The shape of the asteroid Dimorphos was changed.
In a win for planetary defence, NASA's DART mission not only successfully nudged an asteroid off course, but new data reveals it also reshaped the space rock.
DART, short for Double Asteroid Redirection Test, was designed to test our ability to deflect a potential Earth-bound asteroid. In September 2022, DART deliberately slammed into Dimorphos, a small asteroid orbiting a larger one called Didymos. Scientists successfully measured the shift in Dimorphos's orbit around Didymos, proving the mission's deflection technique.
But the surprises didn't stop there. Now, further analysis shows the impact wasn't just a shove-it was a full-on makeover. The tremendous force of the collision appears to have reshaped Dimorphos, transforming it from a somewhat rounded object to something more like an oblong watermelon.
"When DART made an impact, things got very interesting," said Shantanu Naidu, a navigation engineer at NASA's Jet Propulsion Laboratory in Southern California, who led the study. "Dimorphos' orbit is no longer circular; its orbital period"-the time it takes to complete a single orbit-is now 33 minutes and 15 seconds shorter. And the entire shape of the asteroid has changed, from a relatively symmetrical object to a 'triaxial ellipsoid'-something more like an oblong watermelon."
This illustration shows the approximate shape change that the asteroid Dimorphos experienced after DART hit it.
This unexpected finding adds another layer of success to the DART mission, demonstrating that we can not only deflect asteroids but potentially even alter their physical form if needed.
According to NASA, Shantanu Naidu's team used three data sources in their computer models to deduce what had happened to the asteroid after impact. The first source was aboard DART: The spacecraft captured images as it approached the asteroid and sent them back to Earth via NASA's Deep Space Network (DSN). These images provided close-up measurements of the gap between Didymos and Dimorphos while also gauging the dimensions of both asteroids just prior to impact.
The second data source was the DSN's Goldstone Solar System Radar, located near Barstow, California, which bounced radio waves off both asteroids to precisely measure the position and velocity of Dimorphos relative to Didymos after impact. Radar observations quickly helped NASA conclude that DART's effect on the asteroid greatly exceeded the minimum expectations.