The morphological signature of DART ejecta distribution on Dimorphos: Predictions for the Hera encounter

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The kinetic impact of NASA’s Double Asteroid Redirection Test (DART) on Dimorphos generated a massive ejecta cloud, including material with velocities comparable to or lower than the escape speed of the satellite. Most of the low-velocity ejecta is expected to remain gravitationally bound to the Didymos-Dimorphos system and to re-impact Dimorphos within the first 10 hours after the impact. Understanding the fate of this material is essential for interpreting the surface state of Dimorphos at the time of the ESA Hera encounter.In this work, we introduce RAVEL (Regolith Astrodynamics in Variable Effective Low-Gravity Environments), a model particularly well suited for investigating the early post-impact evolution of low-velocity ejecta produced by the DART impact. Here, we apply RAVEL to ejecta with initial velocities of 1-9 cm/s, using a realistic shape model of Dimorphos derived from DART/DRACO observations. We couple three-dimensional orbital dynamics in the binary system with surface transport on shape models of Dimorphos. The model accounts for self-gravity, centrifugal acceleration, Coriolis acceleration, tidal forcing by Didymos, rebounds after surface contact, and friction-controlled sliding. The particles are treated as Lagrangian tracers, allowing us to map the main transport pathways from launch to final deposition without assuming detailed grain-scale properties. We assume a crater radius of 35 m, consistent with current estimates, although this value will be refined after Hera’s arrival. The initial tracers are launched with angles between 24° and 43°, measured with respect to the plane perpendicular to the ejection-cone axis, following DART observations, and with velocity distribution derived from a Housen-Holsapple-type scaling law. Surface motion is computed on the Digital Terrain Model (DTM) derived from DART/DRACO images (Fig.1). Since the DART/DRACO-based DTM only covers the leading hemisphere imaged during the DART encounter, the non-imaged part of Dimorphos is therefore represented as a smooth surface in the model.Fig.1: DART/DRACO-based DTM. The yellow diamond marks the DART impact site. Our simulations show that the dynamics of low-velocity ejecta is highly asymmetric and strongly controlled by the binary environment. Ejecta with the lowest velocities (

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