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Description
The near-Earth binary asteroid (65803) Didymos gained significant scientific attention after the successful impact of NASA's DART mission on its secondary, Dimorphos, validating kinetic impact as a planetary defence strategy (Thomas et al., 2023). This study builds on previous analyses of particle dynamics on Didymos' surface (Trogolo et al.,2023). Using updated physical parameters (Naidu et al., 2024) and a high resolution shape model (Daly et al., 2024), we investigate material lift-off induced by its rapid rotation and mass transference to the secondary.
We assess the asteroid's surface stability by exploring a range of mass and asteroid extents using the reported values, along with their corresponding uncertainties. A total of 25 combinations of mass and volume values were analyzed using numerical simulations, investigating the trajectories and final states of the ejected particles. Four distinct outcomes were identified: reimpact on Didymos (ES1), particles remaining in orbit (ES2), collisions with Dimorphos (ES3), and escape from the system (ES4). Our results show that over 85$\%$ smaller particles ($<$5 $\mu$m radius) quickly return to Didymos, concentrating in equatorial regions, while larger particles ($>$5 cm radius) reach mid-latitudes or higher. Such particles could trigger surface sliding, potentially explaining mass wasting features (Barnouin et al., 2024, Bigot et al., 2024).
Orbiting particles form disk-like structures around Didymos, but absolute density values cannot be derived as they depend on the actual emission mass rate, and may be observationally undetectable. The densest regions are located near 600 meters from the asteroid's center. Over time, solar radiation pressure (SRP) drives smaller particles to form a comet-like tail in the direction opposite to the Sun. Larger particles, less affected by SRP, remain in stable orbits for up to six months. The distribution and dynamics of such particles are the outcome of complex interactions due to Didymos’ irregular shape, fast rotation, and solar radiation pressure.
Material transfer to Dimorphos is also notable, with up to 12$\%$ of the largest particles colliding with its surface at $\sim$ 0.14 m/s, comparable to its escape velocity. Most impacts occur in the trailing hemisphere of Dimorphos, following linear patterns determined by the initial trajectories of the particles.
The ESA Hera mission (Michel et al., 2022), accompanied by the Milani CubeSat carrying the VISTA instrument (Gisellu et al., 2023), will offer a unique opportunity to detect dust particles and volatile materials in the Didymos system. VISTA’s ability to measure particles as small as 10 $\mu$m will be crucial for validating our prediction of dust production and the persistence of fine material in the system's environment. Given the short survival time of fine material, any dust detected by VISTA would support the take-off and landing processes described in this study. These findings could shed light on the dynamics of loose material on fast-rotating small bodies and the interaction between binary asteroid components, enhancing our understanding of resurfacing and orbital processes in binary asteroid systems.