Back in 2022, NASA showed we can deflect asteroids by smashing a spacecraft into an asteroid moon called Dimorphos, which orbits an asteroid called Didymos. It was an impressive feat, and researchers have since been poring over the data from the Double Asteroid Redirection Test (DART), publishing five new studies about the asteroid and its moon. The first study found that Didymos’ surface is rough and covered in massive boulders and craters at high elevations, while it’s much smoother and clearer lower down. The authors estimate the age of the asteroid to be 12.5m years, while its moon is a relative spring chicken at a mere 0.3m years old. Two studies took a closer look Didymos’ and Dimorphos’ surfaces and those boulders, finding the asteroid’s ‘soil’ is weaker and looser than dry sand, and the boulders found on its moon most likely came from Didymos. Together, these three studies lend weight to the theory that Dimorphos formed from material cast off by Didymos. A further study of Dimorphos’ boulders found they break up easily in extreme heat, while the final study found the boulders on Dimorphos are similar to those seen on other asteroids, so they were probably formed in similar ways. We’ve already learned a lot from DART, but we’ll learn even more when the European Space Agency’s upcoming Hera mission takes a peek at the aftermath of NASA’s asteroid smash, the authors conclude.
Journal/conference: Nature Communications
Link to research (DOI): 10.1038/s41467-024-50146-x
Organisation/s: Johns Hopkins University, USA, INAF-Astronomical Observatory of Padova, Italy, Université de Toulouse, France
Funder: See individual papers for funding info.
Media release
From: Springer Nature
Investigating the characteristics of Didymos and DimorphosInsights into the Didymos binary asteroid system, based on observations from NASA’s Double Asteroid Redirection Test (DART) mission, are published across five Nature Communications papers. The findings improve our understanding of the physical and geological characteristics of these planetary bodies, their formation, and have potential implications for future exploration missions and planetary defence strategies.Binary asteroid systems (composed of a main asteroid surrounded by a moon) are of particular interest because they allow for the precise physical characterization of system components and can provide insights into the formation and the evolutionary processes of small body systems. The proximity of Didymos and its moonlet, Dimorphos, to Earth, and the fact that it is a common asteroid type in Near-Earth space, makes it an especially valuable target for research, offering a unique opportunity for close observation. Using data collected by NASA’s DART mission, five research groups investigated different physical characteristics of the Didymos binary asteroid system.Olivier Barnouin and colleagues analysed the geological features and physical properties of Didymos and Dimorphos using NASA’s DART mission data and images from the Italian Space Agency’s Light Italian Cubesat for Imaging of Asteroids (LICIACube) mission. They found that at high elevations, the surface of Didymos is rough and contains large boulders (10–160 metres in length) and craters; at low elevations, the surface is smooth and has fewer large boulders and craters. In comparison, Dimorphos has boulders of a mixture of sizes, several cracks or faults, and a few craters. The authors report that Dimorphos may have formed from material shed by Didymos (that has come together under the influence of gravity) and both have low surface cohesion properties that, with the observed craters, suggest the surface age of Didymos is 40–130 times older than Dimorphos. They estimate the ages of Didymos and Dimorphos are about 12.5 million years and less than 0.3 million years old, respectively.Naomi Murdoch and colleagues analysed boulders tracks on the asteroid surface and determined that the bearing capacity (the ability of a surface to support applied loads) of Didymos’ surface is considerably lower than that of dry sand on Earth or lunar soil. In a separate paper, Maurizio Pajola and co-authors analysed boulder sizes, shapes, and distribution patterns on the surface of the two asteroids. They found that on Dimorphos, boulders exhibited a pattern in their size distribution that suggests they formed in stages, rather than all at once, and were directly inherited from Didymos. This further supports the hypothesis that binary asteroid systems can form through the shedding of material from a primary asteroid.Alice Lucchetti and colleagues found that thermal fatigue can rapidly fracture boulders on the surface of Dimorphos, which may mark the first observation of such rapid (approximately 100,000 years) boulder fracturing by thermal fatigue on this type of asteroid (S-type asteroid). Finally, Colas Robin and co-authors compared the morphology of 34 surface boulders on Dimorphos (ranging from 1.67 to 6.64 metres in size) to those on the surface of several other rubble pile asteroids, including Itokawa, Ryugu, and Bennu. Based on the similarities in boulder morphology, and in comparison with laboratory experiments, their findings suggest a common formation and evolution mechanism for these types of asteroids.Together, the findings provide a comprehensive overview of the Didymos system just prior to the DART mission’s collision with Dimorphos. The findings lay the foundation for the upcoming European Space Agency Hera mission, which should provide higher-resolution data and a more comprehensive examination of the system and the aftermath of DART’s collision.