Abstract:
The surface of Mercury has been heavily modified by impact cratering and volcanic plains since the initial formation of its lithosphere and crust. As in the case of the Moon, the origin of early plains deposits has been difficult to determine because ponded impact basin ejecta and impact melt deposits can mimic the topography and texture of extrusive volcanic plains. In order to understand better the role that impact basins play in resurfacing on Mercury, we used MESSENGER Mercury Dual Imaging System (MDIS) data to map the distribution of plains deposits within and around the relatively young Rembrandt impact basin (~720 km in diameter). There are two different Rembrandt plains units: (1) high-reflectance interior and exterior plains, and (2) low-reflectance exterior plains. The morphology, crater size-frequency distribution, and N(20) crater density were analyzed for each deposit. Observations of the two high-reflectance plains deposits are consistent with previous studies of volcanically produced smooth plains on Mercury. The low-reflectance exterior plains are older than the other high-reflectance plains and comparable in age to the Rembrandt basin impact event. On the basis of age, areal distribution, and albedo relationships with basin materials, the low-reflectance plains are interpreted as basin impact melt deposits. The large areal extent of the low-reflectance plains suggests that basin impact melt deposits may have played an important role in resurfacing Mercury, especially during the early geologic history of the planet when impact rates were higher.
