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When NASA\u2019s DART mission intentionally slammed into Dimorphos in September 2022, the orbit of the moonlet was altered. Researchers have studied the photos and data taken by DART before its impact, learning 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.<\/p>\n
Additionally, the DART researchers concluded both Didymos and Dimorphos are rubble piles, with Dimorphos likely inheriting its boulders from Didymos.<\/p>\n
\u201cIt\u2019s a pile of gravel and boulders (and some sand\/dust) held together by its own gravity, and really not anything else,\u201d said Andy Rivkin, DART investigation team co-lead at the Johns Hopkins Applied Physics Lab (APL), on Bluesky. \u201cThere\u2019s really no cohesion between different pieces of gravel or rocks on Dimorphos.\u201d<\/p>\n
<\/p>\n That makeup explains why DART\u2019s impact made such a such a surprising change in Dimorphos\u2019 orbital period, decreasing it by about 34 minutes. A collection of boulders is easier to shift than a solid object.<\/p>\n Several DART researchers published five papers in Nature Communications, looking at the geology and geophysics of Didymos and Dimorphos as seen by DART.<\/p>\n \u201cThese findings give us new insights into the ways that asteroids can change over time,\u201d said Thomas Statler, lead scientist for Solar System Small Bodies at NASA Headquarters in Washington, in a NASA press release. \u201cThis 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\u2019ve gained from DART.\u201d<\/p>\n In \u201cThe geology and evolution of the Near-Earth binary asteroid system (65803) Didymos,\u201d Olivier Barnouin, Ronald-Louis Ballouz, also of APL, and their team were able to determine the disparate ages of Didymos and Dimorphos. They also found that both objects have weak surface characteristics, which very likely contributed to DART\u2019s significant impact on the moonlet\u2019s orbit.<\/p>\n \u201cThe images and data that DART collected at the Didymos system provided a unique opportunity for a close-up geological look at a near-Earth asteroid binary system,\u201d said Barnouin, in a press release from APL. \u201cFrom these images alone, we were able to infer a great deal of information on 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.\u201d<\/p>\n Images captured by DART and its cubesat companion the LICIACube \u2013 contributed by the Italian Space Agency (ASI)\u00a0 \u2014 showed Dimorphos\u2019 topography 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 inferred that Dimorphos likely spun off from Didymos in a large mass shedding event.<\/p>\n This was confirmed in another paper, \u201cEvidence for multi-fragmentation and mass shedding of boulders on rubble-pile binary asteroid system (65803) Didymos.\u201d Maurizio Pajola, of the National Institute for Astrophysics (INAF) in Rome, and team show how both Didymos and Dimorphos are mainly comprised of a collection of boulders. This team concluded that the formation of Dimorphos likely came as Didymos shed material, creating a new asteroid moonlet.<\/p>\n \u201cThe size-frequency distribution of boulders larger than 5 meters on Dimorphos and larger than 22.8 meters on Didymos confirms that both asteroids are piles of fragments produced in the catastrophic disruption of their progenitors,\u201d the team wrote.\u00a0\u201cThis finding supports the hypothesis that some asteroid binary systems form through the spin up and mass shedding of a fraction of the primary asteroid.\u201d<\/p>\n In another paper, \u201cFast boulder fracturing by thermal fatigue detected on stony asteroids\u201d Alice Lucchetti, also of INAF, and colleagues found that the size and distribution of boulders on Dimorphos is consistant with thermal fatigue, which is the gradual weakening and cracking of a material caused by heat. This could rapidly break up boulders on the surface of Dimorphos, 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.<\/p>\n Thermal fatigue could also have a bearing on what happens if this type of asteroid would need to be deflected for planetary defense.<\/p>\n \u201cThe presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids,\u201d the authors wrote.<\/p>\n Another paper, \u201cThe bearing capacity of asteroid (65803) Didymos estimated from boulder tracks\u201d led by students Jeanne Bigot and Pauline Lombardo of ISAE-SUPAERO in Toulouse, France show that the bearing capacity \u2014 the surface\u2019s ability to support applied loads of asteroid Didymos\u2019 surface is only 0.1% that of dry sand on Earth. NASA said that this is considered an important parameter for understanding and predicting the response of a surface, including for the purposes of displacing an asteroid.<\/p>\n Finally, \u201cMechanical properties of rubble pile asteroids through surface boulder morphological analysis\u201d by Colas Robin, also of ISAE-SUPAERO, and co-authors analyzed the surface boulders on Dimorphos, comparing them with those on other rubble pile asteroids, including Itokawa, Ryugu and Bennu. The researchers found \u201cstiking similarities\u201d the boulders on all four asteroids, suggesting they all formed and evolved in a similar fashion, and were also changed by impacts. This data, too, informs future planetary defense missions or attempts at impactor missions.<\/p>\n \u201cPlanetary defense efforts rely on estimates of the mechanical properties of asteroids, which are difficult to constrain accurately from Earth,\u201d the team wrote. \u201cThe mechanical properties of asteroid material are also important in the interpretation of the DART impact.\u201d \u00a0<\/p>\n All the DART researchers team will continue to observe and study DART\u2019s impact. Additionally, another spacecraft will launch in 2024 to study Dimorphos even closer. ESA\u2019s Hera mission should arrive at Didymos and Dimorphos in December 2026. Hera will undertake a detailed study of Dimorphos to understand more deeply how the impact affected it.<\/p>\nLike this:<\/h3>\n