In September 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully slammed into the side of asteroid moonlet Dimorphos. Initial data from the event indicated that DART had successfully altered the orbit of Dimorphos and achieved its primary mission goal — to assess how much a spacecraft could deflect an asteroid through a transfer of momentum.
However, data analysis didn’t stop, and DART’s science team has released new results and information on why DART was so effective in changing Dimorphos’ orbit and the origins of Dimorphos and its binary asteroid system.
The new results and information were released via five new papers published in Nature Communications. In the papers, DART’s science team explored the geology of Dimorphos and its parent asteroid, Didymos, to characterize the origins of the asteroids and their binary system. Additionally, the team’s research allowed them to learn more about how the binary system evolved and constrain the physical characteristics of the asteroids.
“These findings give us new insights into the ways that asteroids can change over time. This is important not just for understanding the near-Earth objects that are the focus of planetary defense, but also 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,” said Thomas Statler, who serves as the lead scientist for Solar System Small Bodies at NASA Headquarters in Washington D.C.
Using images taken by DART and the LICIACube cubesat, one team — led by Olivier Barnouin and Ronald-Louis Ballouz of the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland — investigated the topography of Dimorphos and found small boulders of varying sizes all across the surface of the moonlet. Interestingly, the larger Didymos featured a smoother surface at lower elevations and a rocky surface at higher elevations. Additionally, Didymos was found to have more craters across its surface than Dimorphos.
These surface characteristics led the team to conclude that Dimorphos likely spun off from Didymos during a large mass-shedding event. The spins of small asteroids can rapidly accelerate through natural processes, and there is growing evidence that these processes may be responsible for re-shaping asteroids and/or forcing material off of their surfaces. If enough material is thrown from the surface, it can reshape itself into a smaller asteroid, much like that of Dimorphos.
The team estimates that Didymos has a surface that is 40 to 130 times older than Dimorphos, with Didymos’ surface being around 12.5 million years old and Dimorphos’ surface being less than 300,000 years old. With Dimorphos’ surface being so young, it is not nearly as strong as Didymos’ surface, which is why DART’s impact likely impacted the moonlet’s orbit so significantly.
“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 were able to infer a great deal of information on the geophysical properties of both Didymos and Dimorphos and expand our understanding on the formation of these two asteroids. We also better understand why DART was so effective in moving Dimorphos,” Barnouin explained.
Figures from Barnouin et al.’s paper. The first three panels (from the left) all highlight the sloping of Dimorphos’ surface. The final panel shows the effects of spin-up disruption on Didymos. (Credit: Johns Hopkins APL/Olivier Barnouin)
In another paper, a team led by Maurizio Pajola of the National Institute for Astrophysics (INAF) in Rome compared the shapes and sizes of various boulders and their distribution patterns across both Dimorphos and Didymos’s surfaces. Pajola et al.’s results showed that the physical characteristics of Dimorphos indicate that the moonlet formed in stages, likely from material inherited from Didymos. These results reinforce the longstanding theory that binary asteroid systems form from the shedding of material from the larger parent asteroid.
The third paper, led by Alice Lucchetti of INAF, revealed that thermal fatigue, or the gradual weakening and cracking of a material due to heat, could rapidly break up boulders on the surface of Dimorphos. The breaking of these boulders could generate surface lines and alter the physical characteristics of asteroids similar to Dimorphos more rapidly than previously thought. Lucchetti et. al. believe that DART’s observations were likely the first time this phenomenon has ever been observed on this type of asteroid.
Led by students Jeanne Bigot and Pauline Lombardo, the fourth paper explored and determined Didymos’ bearing capacity, or an asteroid’s surface’s ability to support applied loads. The students found Didymos’ bearing capacity to be 1,000 times lower than that of dry sand on Earth or lunar soil on the Moon. Information on an asteroid’s bearing capacity can prove to be very useful for understanding and predicting the response of a surface to different events, including displacing and removing an asteroid from its orbit.
A new spin on asteroid formation: how observations from the #DARTMission are refining our understanding of how some binary asteroid pairs come to be https://t.co/yYyEjINqeg pic.twitter.com/Dj9JhvrozL
— NASA Solar System (@NASASolarSystem) July 30, 2024
The fifth and final paper, led by Colas Robin of ISAE-SUPAERO, investigated and analyzed the surface boulders on Dimorphos and compared them to those on other “rubble pile” asteroids like Ryugu, Itokawa, and Bennu. Robin et al. found that the boulders all shared similar characteristics, which suggests that all of these rubble pile asteroids formed and evolved in similar ways. The team also mentioned that the elongated nature of boulders and other surface materials around the DART impact site likely means that they were formed through impact processing.
These papers provide a more robust overview of not only how the Didymos system formed but also how asteroids and binary systems similar to it formed in our solar system. When the European Space Agency’s (ESA) Hera mission visits the DART impact site at Dimorphos in 2026, the spacecraft will further analyze the aftermath of the impact, and these five papers help provide the necessary context and information that Hera’s teams will need to properly assess the impact site. Additionally, the research adds to scientists’ understanding of planetary science and asteroid characteristics — vital information needed for understanding our solar system, its origins, and how it has evolved.
(Lead image: Artist’s rendering of DART before impacting Dimorphos. Credit: NASA)