Surface Features of Didymos and Dimorphos from Dart and Liciacube Missions

Resumen

On September 26th, 2022, NASA's DART (Double Asteroid Redirection Test) mission performed the first demonstration of a kinetic impact deflection for planetary defense purposes by impacting the ~160 m S-type asteroid Dimorphos, the secondary body of the near-Earth binary asteroid (65803) Didymos (780 m-size). Before and after impact, DART, along with the LICIAcube spacecraft, provided exceptional close-up images of both Didymos and Dimorphos, revealing oblate shapes and rocky surfaces for both asteroids [1]. During the last minutes and up to two seconds before the impact, the DRACO camera aboard DART captured high-resolution images of Dimorphos at different spatial scales. Peak resolution ranges from ~3.9 m/pixel for Didymos, and ~0.055 m/pixel for Dimorphos at the impact site. Here, we present current assessments of the surfaces and features of Didymos and Dimorphos and explore the possible processes responsible for their geological formation and evolution. On Didymos, we can distinguish two geological regions [2]. The first region that covers mid-to-low latitudes is characterized by a lack of large boulders (>25 m) and particularly differentiated smooth terrains at the equator. This region possesses features that are interpreted to be surface mass movements [2]. The second region is more hummocky and is located at mid-to-high latitudes; it possesses a greater number of large boulders and concavities. Some of these concavities could be candidates for large impact craters; and if confirmed, would be an equivalent or slightly lower ratio to other debris pile asteroids in terms of size-to-asteroid size ratio [3, 4]. On Dimorphos, current analyses show no distinct geological units, at least in the hemisphere imaged by DRACO. The surface is dominated by boulders (between tens of cm up to ~16 m), and no fine regolith is evident [5]. Some boulders appear to be arranged in partially circular and concentric arrangements. There is evidence for rocks resting on boulders, but never at slopes exceeding 30° [2]. We also found several buried boulders or possible evidence of fractured pieces by impacts. Despite the limitations of the viewing geometry, lineaments have been identified across the asteroid; some of these might be associated with smaller cracks or fractures seen on individual blocks [6], and others go through directions preferentially NE-SW furrowing tens of meters on the Dimorphos's surface.