Mare Marginis

Mare Marginis. A lunar mare located on the extreme eastern limb of the Moon as seen from Earth, making it a challenging feature for terrestrial observation. Its position straddles the border between the near side and the far side, creating a unique geological setting. The mare's name, meaning "Sea of the Edge," directly references its peripheral location on the lunar disk.

Characteristics

Mare Marginis is an irregularly shaped basin with a relatively low albedo compared to the surrounding highlands, indicative of its basaltic composition. It is notably adjacent to several prominent impact craters, including Goddard to the north and Al-Biruni to the south, which punctuate its borders. The mare's surface is intersected by faint wrinkle ridges and is notably non-circular, lacking the well-defined ringed structure of larger basins like Mare Imbrium. A distinctive feature within its confines is the unusual, dark-haloed crater Al-Tusi, which suggests excavation of subsurface mare material.

Exploration

Detailed knowledge of Mare Marginis was significantly advanced by orbital missions, particularly the Lunar Orbiter program in the 1960s, which provided the first high-resolution imagery of this limb region. The Apollo program did not target this area directly, but later missions like Clementine and the Lunar Reconnaissance Orbiter have extensively mapped its topography and mineralogy. Data from the Kaguya mission and Chandrayaan-1 have further contributed to understanding its surface properties and composition, revealing it to be rich in ilmenite.

Geology

The geology of Mare Marginis is dominated by mare basalt flows, which are thinner and potentially older than those found in major central nearside maria. Spectral analysis indicates the presence of pyroxene and olivine in its basalts, with significant iron and titanium oxide content. The region exhibits a complex tectonic history, with its wrinkle ridges suggesting compressional stresses following the volcanic flooding. The proximity to the South Pole–Aitken basin, one of the largest and oldest impact structures in the Solar System, likely influenced its subsurface structure and magma pathways.

Origin and Age

Mare Marginis is believed to have formed within a pre-existing impact basin of uncertain origin, possibly related to the Nectarian-period bombardment. Radiometric dating of returned samples from other maria, coupled with crater counting techniques applied to its surface, suggest its basalts erupted during the Late Imbrian epoch, approximately 3.5 to 3.8 billion years ago. This places its volcanic activity slightly later than the major flooding of Mare Serenitatis but contemporaneous with the later phases of volcanism in Mare Crisium. The basin's location on the thin crust of the lunar limb may have facilitated the ascent of magma from the mantle.

Observation and Naming

Due to its location, Mare Marginis is subject to extreme libration, occasionally tilting more fully into view from Earth but often remaining highly foreshortened. It was historically difficult to study through telescopes like those at the Mount Wilson Observatory. The feature was named by the International Astronomical Union following the tradition of Giovanni Battista Riccioli's 17th-century lunar nomenclature, where "mare" denotes a perceived sea. Its official designation was formalized in the IAU's inaugural lunar catalog, solidifying its identity among other marginal maria like Mare Australe.

Category:Lunar maria