Asteroid Dimorph looks completely different after being hit by NASA’s DART probe

In September 2022, a NASA spacecraft crashed into a tiny asteroid to slightly change its orbit. While the mission successfully tested a method for deflecting asteroids that may one day be useful, instead of creating an impact crater, the impact completely changed the shape of the target asteroid, revealing its plasticity.



A team of researchers simulated the impact of NASA’s Double Asteroid Redirection Test (DART) with an asteroid to understand exactly how it could transform Dimorph, a 170-meter-diameter cosmic rock that orbits its 800-meter-diameter moon Didymos. A new study published in Nature Astronomy shows that the impact caused a significant change in the shape and surface of Dimorph.


Our simulations revealed that Dimorph is most likely a debris pile asteroid. Before DART arrived at Dimorph, we didn’t know what to expect because the system is so far from Earth.



— Sabine Raducan, planetary scientist at the University of Bern (Switzerland), lead author of the paper

On September 26, 2022, after a 10-month flight, NASA’s 1.3-ton probe crashed into an asteroid. Data from ground-based optical and radio telescopes show that after the collision, Dimorph’s orbital period around Didyma was reduced from 11 hours 55 minutes to 11 hours 23 minutes.


Using the Bern Smoothed Particle Hydrodynamics (SPH) impact simulation code, the team ran 250 simulations to reproduce the asteroid’s behavior during the first two hours after impact. Scientists estimate that about 1% of Dimorph’s total mass was ejected into space after the collision with DART, and about 8% of the mass “flowed” across its surface.


These results show not only possible changes to the asteroid after the probe impact, but also the internal structure of Dimorph itself. The study suggests that it is an asteroid made from a pile of small debris, held together by its own weak gravity rather than internal strength. Therefore, the DART impact created a very wide cone-shaped ejection of material that spread out to 160 degrees and continued to expand due to the weak gravity and low internal cohesion of the asteroid.

The results also suggest that the small Dimorph likely formed from material that broke away from Didymus and then accreted around it, becoming a sort of mini-moon.


The European Space Agency (ESA) is planning a new mission to this pair of asteroids to better study Dimorph’s changes after the DART collision. The HERA mission is scheduled to launch in 2024, and rendezvous with Didim and its moon is scheduled for 2026.


Further observations could provide insight into the formation of asteroids and help improve methods for deflecting dangerous objects in the event of a threat of impact with Earth.



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