The dark regions are the lunar maria, whereas the lighter regions are the highlands. While many of the basalts either erupted within, or flowed into, low-lying impact basins, the largest expanse of volcanic units, Oceanus Procellarum, does not correspond to any known impact basin.Ī global albedo map of the Moon obtained from the Clementine mission. The few basaltic eruptions that occurred on the far side are old, whereas the youngest flows are found within Oceanus Procellarum on the nearside. Nevertheless, the majority of mare basalts appear to have erupted between about 3 and 3.5 Ga. The radiometric ages range from about 3.16 to 4.2 billion years old (Ga), whereas the youngest ages determined from crater counting are about 1.2 Ga. The ages of the mare basalts have been determined both by direct radiometric dating and by the technique of crater counting. When Mare Moscoviense was discovered by the Luna 3, and the name was proposed by the Soviet Union, it was only accepted by the International Astronomical Union with the justification that Moscow is a state of mind. Mare Humboldtianum and Mare Smythii were established before the final nomenclature, that of states of mind, was accepted, and do not follow this pattern. The names of maria refer to sea features ( Mare Humorum, Mare Imbrium, Mare Insularum, Mare Nubium, Mare Spumans, Mare Undarum, Mare Vaporum, Oceanus Procellarum, Mare Frigoris), sea attributes ( Mare Australe, Mare Orientale, Mare Cognitum, Mare Marginis), or states of mind ( Mare Crisium, Mare Ingenii, Mare Serenitatis, Mare Tranquillitatis). The last three are smaller than maria, but have the same nature and characteristics. The traditional nomenclature for the Moon also includes one oceanus (ocean), as well as features with the names lacus ('lake'), palus ('marsh'), and sinus ('bay'). The few maria on the far side are much smaller, residing mostly in very large craters. The maria cover about 16% of the lunar surface, mostly on the side visible from Earth. They are less reflective than the "highlands" as a result of their iron-rich composition, and hence appear dark to the naked eye. They were dubbed maria ( Latin for 'seas'), by early astronomers who mistook them for actual seas. ə/ MAR-ee-ə SG mare / ˈ m ɑːr eɪ/ MAR-ay) are large, dark, basaltic plains on Earth's Moon, formed by ancient asteroid impacts on the far side on the Moon that triggered volcanic activity on the opposite (near) side. The near side of the Moon, with major maria and craters labeled
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