Mairan (crater)
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 Lunar Orbiter 4 image | |
| Coordinates | 41°36′N 43°24′W / 41.6°N 43.4°W |
|---|---|
| Diameter | 40 km |
| Depth | 3.4 km |
| Colongitude | 44° at sunrise |
| Eponym | Jean J. d'Ortous de Mairan |
Mairan is a lunar impact crater that is located on a highland peninsula between Oceanus Procellarum to the west and Mare Imbrium to the east. To the north-northeast is the comparably sized crater Sharp. Northwest of Mairan is the heavily eroded Louville.
The outer rim of Mairan has not been significantly eroded or impacted, and retains a sharp edge. The surface around Mairan is rough and irregular, with a multitude of many tiny craters, particularly to the south and west. The inner walls display some terracing, and flow down to a relatively flat interior floor.
The volcanic complex, known as Mairan Hills or Mairan Domes, is composed of Mairan T together with three satellite domes (Mairan Northwest, Mairan Middle, and Mairan South). It was formed by two volcanic episodes 3.75±0.1 and 3.35±0.2 billion years ago, extruding a viscous silicic lava simultaneously with basalt eruptions in nearby mare. Most of volcanic complex, except for dome summits, is now buried under mare surface.[2]
In the mare, due west of Mairan, is a small lunar dome designated Mairan T with 3.8 km wide depression at the summit (in official IAU nomenclature "Mairan T" name refers only to the depression), believed to be a caldera[3] The width of hill is about 7 km, and height is about 800 m.[4] It is one of four unusually steep (with slopes reaching 22-27 degrees) and bright domes in area which are thought to be formed by very viscous, high-Si lava.[5]
The composition of domes is changing from the north to south, with Mairan Northwest composed of pyroxenes with 30% quartz admixture, while Mairan South dome composed of nearly pure quartz, with extremely high thorium concentration of 83±19 ppm.[6]
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