While studying data from NASA’s DART mission, which impacted its asteroid Dimorphos in 2022, the mission’s science team has discovered new information on the origins of the target binary asteroid system. The team also determined how the DART spacecraft effectively shifted Dimorphos’ orbit.
The team studied the geology of the binary asteroid system- the moonlet Dimorphos and the main asteroid Didymos- to ascertain how they formed and evolved and also understand their physical properties.
The results offer new information on how asteroids can change over time and provide a new understanding of the near-Earth objects that are the focus of planetary defense.
Thomas Statler, lead scientist for Solar System Small Bodies at NASA Headquarters in Washington, said, “This is also important for our ability to read the history of our Solar System from these remnants of planet formation. This is just part of the wealth of new knowledge we’ve gained from DART.”
After analyzing the geology of both asteroids, the team concluded their surface materials and interior properties. Using images from the DART spacecraft and its LICIACube cubesat, the team studied Dimorphos’ surface, noting that it has boulders of different sizes.
In contrast, the giant asteroid Didymos had smoother, less rocky lower areas but was more rugged and cratered higher. The authors suggested that Dimorphos probably broke away from Didymos during a significant mass-shedding event.
Some natural processes can accelerate the rotations of minor asteroids. Growing evidence suggests that these processes can reshape these bodies or even force the material to be spun off their surfaces.
Based on scant surface characteristics, the team concluded that Didymos is 40–130 times older than Dimorphos, with the former estimated to be 12.5 million years old and the latter less than 300,000 years old. Dimorphos’s poor surface strength most certainly contributed to DART’s major orbital impact.
Olivier Barnouin of Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, said, “The images and data that DART collected at the Didymos system provided a unique opportunity for a close-up geological look of a near-Earth asteroid binary system. From these images alone, we could infer a great deal of information on the geophysical properties of both Didymos and Dimorphos and expand our understanding of the formation of these two asteroids. We also better understand why DART was so effective in moving Dimorphos.”
In a paper comparing the shapes and sizes of the various boulders and their distribution patterns on the two asteroids’ surfaces, the team determined Dimorphos’s physical characteristics. They found it formed in stages, likely of material inherited from its parent asteroid, Didymos.
This conclusion supports the idea that some binary asteroid systems form when a giant primary asteroid sheds material that gathers into a new moonlet.
The team discovered that thermal fatigue—weakening and cracking caused by heat—could quickly break up boulders on Dimorphos, changing its surface and physical features faster than expected. The DART mission likely provided the first observation of this process on this kind of asteroid.
The next paper- which focuses on Didymos’ bearing capacity- found that the surface’s ability to support applied loads is at least 1,000 times lower than that of dry sand on Earth or lunar soil. This is an essential parameter for understanding and predicting a surface’s response, including for displacing an asteroid.
After analyzing the surface boulders on Dimorphos and comparing them with those on other rubble pile asteroids, including Itokawa, Ryugu, and Bennu, the team found that the boulders shared similar characteristics. This means that all such asteroids formed and evolved in a similar fashion.
Researchers noted, “The elongated nature of the boulders around the DART impact site implies that they were likely formed through impact processing.”
“These most recent discoveries contribute to our understanding of the formation of such planetary bodies and provide a more comprehensive picture of the Didymos system’s origins. This research tests what ESA’s Hera mission will find and strengthen planetary defense capabilities while supporting current and future exploration missions. As the mission gets ready to revisit the collision site of DART in 2026, further analyze the aftermath of the first-ever planetary defense test.”
The findings are presented in five papers in Nature Communications.