When NASA's DART mission Intentionally collided with Dimorphos in September 2022The moon's orbit was altered. Researchers have studied photos and data taken by DART before the impact, which has helped them learn more about the geology of the Didymos/Dimorphos system. They have now estimated the surface age of both the asteroid and its moon. The asteroid Didymos has a surface age of 12.5 million years, while the moon Dimorphos is only 300,000 years old.
Furthermore, DART researchers concluded that both Didymos and Dimorphos are rubble piles, and that Dimorphos likely inherited its rocks from Didymos.
“It's a bunch of gravel and rocks (and some sand/dust) held together by their own gravity, and really nothing else,” said Andy Rivkin, co-leader of the DART research team at the Johns Hopkins Applied Physics Laboratory (APL). in Bluesky“There is really no cohesion between different pieces of gravel or rocks in Dimorphos.”
That makeup explains why The DART impact produced a surprising change in Dimorphos' orbital period, decreasing it by about 34 minutes. A collection of rocks is easier to move than a solid object.
Several DART researchers published five papers in Nature Communications, analyzing the geology and geophysics of Didymos and Dimorphos as observed by DART.
“These findings give us new insights into the ways asteroids can change over time,” said Thomas Statler, lead scientist for Small Solar System Bodies at NASA Headquarters in Washington. in a NASA press release. “This is important not only 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 planetary formation. This is just one part of the wealth of new knowledge we have gained from DART.”
In “The Geology and Evolution of the Near-Earth Asteroid Binary System (65803) Didymos” Olivier Barnouin, Ronald-Louis Ballouz, also of APL, and their team were able to determine the different ages of Didymos and Dimorphos. They also discovered that both objects have faint surface features, which most likely contributed to DART's significant impact on the moon's orbit.
“The images and data that DART collected in the Didymos system provided a unique opportunity for a close-up geological look at a near-Earth binary asteroid system,” said Barnouin, in an APL press release. “From these images, we were able to infer a wealth of information about the geophysical properties of Didymos and Dimorphos, and expand our understanding of the formation of these two asteroids. We also better understand why DART was so effective at moving Dimorphos.”
Images captured by DART and its The cubesat companion, the LICIACube – contributed by the Italian Space Agency (ASI) – showed that Dimorphos’ topography was covered with boulders of varying sizes, while the larger asteroid Didymos was smoother at lower elevations, though rocky at higher elevations. It also had more craters than Dimorphos. The authors deduced that Dimorphos likely broke off from Didymos in a large mass-shedding event.
This was confirmed in another article, “Evidence for multiple fragmentation and massive rockfall in the debris pile binary asteroid system (65803) Didymos.Maurizio Pajola of the National Institute for Astrophysics (INAF) in Rome and his team show that both Didymos and Dimorphos are composed primarily of a set of rocks. This team concluded that the formation of Dimorphos likely occurred when Didymos shed material, creating a new asteroid moon.
“The size frequency distribution of blocks larger than 5 meters in Dimorphos and larger than 22.8 meters in Didymos confirms that both asteroids are fragment piles produced in the catastrophic breakup of their progenitors,” the team wrote. “This finding supports the hypothesis that some binary asteroid systems form through velocity boosting and mass shedding of a fraction of the parent asteroid.”
In another article, Rapid fracture of rocks due to thermal fatigue detected in rocky asteroids Alice Lucchetti, also of INAF, and her colleagues found that the size and distribution of rocks on Dimorphos are consistent with thermal fatigue, which is the gradual weakening and cracking of a material caused by heat. This could rapidly break down rocks on Dimorphos’ surface, generating surface lines and altering the physical characteristics of this type of asteroid more quickly than previously thought. The DART mission was likely the first observation of such a phenomenon on this type of asteroid.
Thermal fatigue could also influence what would happen if this type of asteroid needed to be diverted for planetary defense.
“The presence of thermally fractured rock fields on near-Earth asteroid surfaces may contribute to an increase in the ejected mass and momentum of kinetic impactors when deflecting asteroids,” the authors wrote.
Another article, “Carrying capacity of asteroid (65803) Didymos estimated from rock footprints” A study led by ISAE-SUPAERO students Jeanne Bigot and Pauline Lombardo in Toulouse, France, shows that the load-bearing capacity of the surface of the asteroid Didymos is only 0.1 percent of that of dry sand on Earth. NASA said this is considered an important parameter for understanding and predicting the response of a surface, including to the effects of asteroid displacement.
Finally, “Mechanical properties of asteroids formed by debris through morphological analysis of surface rocks” Colas Robin, also of ISAE-SUPAERO, and other authors analyzed rocks from Dimorphos’ surface and compared them to those from other debris-laden asteroids, including Itokawa, Ryugu, and Bennu. The researchers found “striking similarities” between the rocks from the four asteroids, suggesting they all formed and evolved in similar ways and were also modified by impacts. These data also inform future planetary defense missions or attempted impact missions.
“Planetary defense efforts rely on estimates of asteroid mechanical properties, which are difficult to accurately determine from Earth,” the team wrote. “Mechanical properties of asteroid material are also important for the interpretation of the DART impact.”
The entire DART research team will continue to observe and study the DART impact. In addition, another spacecraft will be launched in 2024 to study Dimorphos even more closely. ESA's Hera mission is expected to arrive at Didymos and Dimorphos in December 2026. Hera will conduct a detailed study of Dimorphos to better understand how the impact affected it.
