On September 26, 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid Didymos. New numerical simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos.
The asteroid moonlet Dimorphos as seen by NASA’s DART spacecraft 11 seconds before impact. DART’s on board DRACO imager captured this image from a distance of 68 km (42 miles). This image was the last to contain all of Dimorphos in the field of view. Image credit: NASA / Hopkins Applied Physics Laboratory.
DART was a planetary defense mission to demonstrate the feasibility of using a kinetic impactor to change the trajectory of an asteroid.
The impact was successful and highly effective, resulting in a reduction in Dimorphos’ orbital period around Didymos, which was initially 11 h and 55 min, by 33 min.
The LICIACube Unit Key Explorer (LUKE) instrument onboard the cubesat captured images of the system between 29 and 320 s after impact to reveal filamentary streams of ejecta and other complex patterns that expanded for several km from the impact site.
Moreover, the dramatic brightening of the Didymos system by solar illumination of released impact ejecta was observed by ground- and space-based telescopes for many weeks after the impact.
These three Hubble images capture the breakup of Dimorphos when it was deliberately hit by DART on September 26, 2022. The top panel, taken 2 hours after impact, shows an ejecta cone (an estimated 1,000 tons of dust). The center frame shows the dynamic interaction within the Didymos-Dimorphos binary system that starts to distort the cone shape of the ejecta pattern about 17 hours after the impact. The most prominent structures are rotating, pinwheel-shaped features. The pinwheel is tied to the gravitational pull of Didymos. In the bottom frame, Hubble captures debris being swept back into a comet-like tail by the pressure of sunlight on the tiny dust particles. This stretches out into a debris train where the lightest particles travel the fastest and farthest from the asteroid. The mystery is compounded when Hubble records the tail splitting in two for a few days. Image credit: NASA / ESA / STScI / Jian-Yang Li, PSI / Joseph DePasquale, STScI.
In new research, University of Bern scientist Sabina Raducan and her colleagues modeled the DART impact with a state-of-the-art shock physics code, using realistic constraints on Dimorphos’ mechanical and compositional properties informed by DART’s first results.
The simulations that were the closest match to observations of the impact suggest that Dimorphos is weak with a cohesive strength similar to the asteroids Bennu and Ryugu and has a lack of large boulders on its surface.
The researchers suggest that Dimorphos may be a rubble pile formed from rotational shedding and re-accumulation of ejected material from Didymos.
Their model also indicates that the DART impact may not have produced an impact crater but could have reshaped the moon in its entirety — a process known as global deformation — and caused resurfacing of Dimorphos with material from its interior.
The findings offer additional insights into the formation and characteristics of binary asteroids and may have implications for future explorations, such as ESA’s Hera mission, and asteroid deflection efforts.
“ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater,” the authors concluded.
Their paper was published in the journal Nature Astronomy.
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S.D. Raducan et al. Physical properties of asteroid Dimorphos as derived from the DART impact. Nat Astron, published online February 26, 2024; doi: 10.1038/s41550-024-02200-3