Geology of the Moon's Surface

Don't KREEP Out! What's the Geology of the Moon's Surface?

Our planet's only natural satellite―the Moon―is also the only celestial body that has witnessed a manned landing. Research on the geology of the Moon's surface, also referred to as selenology, reveals a surface that is devoid of tectonics. The complexity of the geomorphology is as interesting as the lunar samples obtained.
The Moon or 'Luna' is the fifth-largest satellite in the solar system. This natural satellite makes one complete revolution around the Earth every 27.3 days. The satellite has a diameter of 3,474 km, and a surface area that is about a quarter that of the Earth. Its volume is approximately 2% that of Earth, while exerted gravitational pull measures at about 17% that on the Earth's surface.
History of the Moon
The Moon possesses an iron core that roughly measures around 25% of its radius. The lunar geologic timescale highlights remnants and proof of the initial molten state of the satellite. The ellipsoid formation, as we know the Moon today, resulted on account of tidal forces. Crystallization of the magma ocean on its surface reveals a depth of 500 km or more. Research reveals that iron, pyroxene, olivine, and magnesium silicates were the first minerals to form in this magma ocean. Subsequent crystallization resulted in the formation of an anorthositic plagioclase feldspar crystallization of lesser density that formed the Moon's anorthositic crust. The crust is around 50 km in thickness. The KREEP rich magma (acronym for 'K' - atomic symbol for potassium, 'REE' - Rare Earth Elements and P - phosphorus) concentrated within the Oceanus Procellarum and Imbrium basin regions. This area on the surface is also referred to as the Procellarum KREEP Terrane.
After the formation of the lunar crust, different types of magmas resulted in formation of Mg-suite norites and troctolites in the Procellarum KREEP Terrane. Analysis of lunar samples reveal that the lunar impact basins were formed between about 4 and 3.85 Ga ago. The lunar maria or basaltic plains contain rich deposits of iron and the titanium-rich mineral, ilmenite. Pyroclastic eruptions spewed molten basaltic materials hundreds of kilometers away, forming impact basins. Meteorite and comet impacts have resulted in the stress variations observed on the surface of the Moon. The surface area is exposed to consistent space weathering triggered by high energy solar particles, solar winds, and micrometeorite impacts. The landscape is characterized by volcanoes, hills, impact craters and ejecta, and magma-filled depressions.
Moon Surface
The geology of the Moon, or selenology, is very different from that of the Earth. It does not have an atmosphere or water bodies. This totally eliminates the presence of any form of erosion triggered by weather. The surface does not comprise plate tectonics, and due to its small size and lower gravity, the Moon's surface cools more rapidly. The satellite has a geomorphology that comprises a combination of processes, such as volcanism and impact cratering. Like the Earth, the Moon too has a core, mantle, and crust. Geological studies of the acquired lunar samples and geophysical data reveal that the surface of the Moon has an elemental composition of oxygen, iron, silicon, calcium, magnesium, aluminum, titanium, and manganese. Carbon and nitrogen are only present in trace quantities, and that too on account of deposition by solar wind. Hydrogen is concentrated at both the poles. The origin of the satellite is narrowed down to the effects of fission, co-accretion, and impact hypothesis. The Moon's mean surface temperature during the day is approximately 107 °C, while that at night is around -153 °C. The maximum surface temperature recorded is 123 °C, with a minimum of -233 °C.