Analysis of the Relative Geological Ages of the Lunar Maria

Abstract:

Lunar Maria are large, dark, plain areas on the lunar surface mostly covered by basaltic, which are formed by ancient volcanic eruptions, and 23 lunar maria have been named. There are mainly two methods used to determine the ages of the planet surface which are radiometric dating (Papike et.al., 1998) and crater counting (Hiesinger et.al. 2000, 2003). As for the lunar surface, some scientists have study the ages of the lunar mare basalts with these methods, however, since the boundaries of the lunar maria have not been defined, so that there are few study on the relative ages among the named lunar maria from a geographic area perspective. In this approach, we detected the boundaries for each named lunar mare and analysis the relative ages for them with the crater counting method.In detecting the boundaries of the lunar maria, some lunar image data and topographic data were collected from Chang’E1 program data, such as the lunar global DOM data with a resolution of 120m, and the global DEM data with a resolution of 500m. For the crater counting, some crater data were downloaded from the website (http://planetarynames.wr.usgs.gov/SearchResults?target=Moon&featureType=Crater,%20craters). Based on the global lunar DEM and DOM data, the images were classified into lunar mare and highland with maximum likelihood classification method, after that, ArcMap 3D Analyst tool was used to extract each lunar mare, then the boundaries of 23 named lunar maria were detected.With the crater data and the lunar mare boundaries, the number of the craters in each lunar mare could be counted, and the summarize area of the craters in each mare could also be calculated with the diameter attribute in the crater data. Some attributes of each lunar mare were shown as Tab.1.After that, we calculated the value by dividing the area of each mare with the area of the craters in the mare, and then the value was visualized in a global lunar map, as shown in Fig.1. The bigger value stands for more crater frequency, which means the geologic age of the mare might be relatively older.The result shows that some maria in the farside such as the Mare Ingenii might be older than others. Since the result depends a lot on the precision of craters data, so in the future research, we should extract the craters from other lunar global images with higher resolution.