Le Monnier (crater)

Le Monnier (crater) is a lunar impact crater located on the northeastern edge of Mare Serenitatis. It is named for the French astronomer Pierre Charles Le Monnier and is notable for being the landing site of the Soviet Luna 21 mission, which delivered the Lunokhod 2 rover. The crater's floor has been flooded by basaltic lava, making it a flat, bay-like feature along the mare's border.

Description

Le Monnier is a flooded crater formation, classified as a lunar mare-filled basin on the border of Mare Serenitatis. Its intact rim is most prominent along the western and southern sections, where it rises above the surrounding lava plains, while the eastern wall is largely submerged and breached, allowing the mare lavas to inundate the interior. The floor is exceptionally smooth and dark, consistent with the basaltic composition of the adjacent Mare Serenitatis, and is marked by a few low ridges and secondary crater chains. The crater's morphology places it within the Erathosthenian period of the lunar geologic timescale, indicating it was formed after the Imbrium Basin but before the youngest mare flows.

Exploration

The primary significance of Le Monnier in lunar exploration stems from the successful Soviet space program mission, Luna 21. Launched in January 1973, the spacecraft landed on the crater's flat floor on January 15, deploying the Lunokhod 2 rover. This robotic vehicle conducted extensive photographic and soil analysis surveys, traveling over 42 kilometers and returning valuable data on the lunar soil and surface mechanics. The mission provided critical ground-truth observations that complemented orbital data from American programs like Apollo 15 and Apollo 17, which also imaged the region. The landing site was chosen for its geologic accessibility to both mare and highland materials.

Geological features

The geology of Le Monnier is dominated by mare basalt flows from Mare Serenitatis, which have extensively modified the original crater structure. Spectral data from missions like Clementine (spacecraft) suggest the basalts here are typical of the eastern Serenitatis region. Key features within and around the crater include wrinkle ridge systems, such as those associated with the Serenitatis basin tectonics, and bright ray material from distant impacts like Tycho (crater). The breached eastern rim provides a window into the stratigraphy, potentially exposing pre-mare lunar highlands material. Lunokhod 2 directly analyzed the soil, confirming the presence of pyroxene and plagioclase minerals common to mare basalts.

Location and surroundings

Le Monnier is situated in the northeastern quadrant of the Moon's near side, with its eastern rim bordering the rugged Taurus Mountains. It lies southeast of the prominent crater Posidonius and northwest of the smaller, sharp-rimmed Dawes. The region is part of a complex geologic boundary between Mare Serenitatis and the Mare Crisium basin to the northeast. Nearby notable features include the Littrow region, explored by Apollo 17, and the Vitruvius crater. This location places it at the junction of several major lunar terrains, making it a site of significant geologic interest.

Satellite craters

By convention, smaller associated craters are identified on lunar maps by a letter placed on the side of the crater midpoint closest to Le Monnier. The most notable of these include: * Le Monnier B: A small, bowl-shaped crater on the mare to the northwest. * Le Monnier K: Located on the inundated eastern rim segment. * Le Monnier L: A distinct craterlet on the southern floor. These satellite craters, along with others like Le Monnier F and Le Monnier G, provide additional context for understanding the impact history and stratigraphy of the area, as their freshness contrasts with the heavily modified main crater.

Category:Impact craters on the Moon