There Are Two Geologically Distinct Plains Regions On Mercury

Another interesting facts about Mercury is there are two geographically distinct plains regions. Mercury's earliest visible surfaces are gently sloping, hilly plains, which predate the topography that is highly cratered. These inter-crater plains indicate a general lack of smaller craters with diameters less than around 30 km and appear to have destroyed numerous earlier craters.

The lunar maria are similar to smooth plains, which are extensive flat expanses that fill depressions of different sizes. The smooth plains of Mercury have the same albedo as the earlier inter-crater plains, in contrast to lunar maria. Even though these plains lack unmistakably volcanic traits, their location and rounded, lobate shape clearly suggest that they have volcanic origins. As seen by noticeably lower crater density than on the Caloris ejecta blanket, all of Mercury's smooth plains developed much later than the Caloris basin.