Volcanic Material or Impact Ejecta?
The origin of the plains material that covers large areas of the surface of Mercury is not well understood. Some planetary scientists believe that at least some of the plains are made up of material blown out of ancient impact basins (ejecta). Others believe some plains are made up of volcanic material that flooded the cratered terrain and filled topographic depressions. There are problems with both ideas. If the plains are ejecta material, it would have to come from many large impact basins but only one (Caloris) has been found. If volcanism is the source of the plains, volcanic landforms should be present but there are no obvious examples.
Color Composite Image
How can planetary scientists determine if the smooth plains on Mercury are volcanic in origin or made up of impact ejecta? One way is to use color information about the surface materials obtained from the Mariner 10 images. This color composite image was made using information derived from ultraviolet and orange color data. The colors in this image reflect different chemical and physical properties of the surface materials. In some areas the colors define surface units with the characteristics of volcanic material that has flowed into and around impact craters. This suggests that at least some of the mercurian smooth plains are the products of volcanism.
Image courtesy of M.S. Robinson
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