FEATURES OF VOLCANIC ACTIVITY ON THE MOON

The Moon is the closest large celestial body to us and one of the most studied objects in the Solar System. Due to the absence of plate tectonics, atmosphere and biosphere, the Moon's surface has preserved traces of intense meteorite bombardment and large-scale volcanism. The study of the Moon, starting from its general physical parameters and ending with the details of its internal structure and volcanic evolution, allows us to reconstruct its own history and shed light on the early stages of the development of the Earth and other planets. The average radius of the Moon is 1737.1 km. The Moon has a very low reflectivity with an albedo of about 0.11. The Moon's surface experiences temperature fluctuations from +130 °C during the day to -170 °C at night. It revolves around the Earth in an elliptical orbit for 27.32 Earth days at an average distance of 384,400 km. Due to tidal capture, the Moon always faces the Earth with the same hemisphere. Current models of the Moon's interior are based on data from “Apollo” seismic experiments, measurements of the Moon's gravity field and laser ranging, and analyses of lunar samples returned by the “Apollo” missions and lunar stations. The Moon's differentiated structure, with its distinct crust, mantle, and core, is the result of the fractional crystallization of a global magma ocean that existed shortly after its formation. This process caused heavier minerals (olivine and pyroxene) to sink to the center, forming the mantle, and lighter minerals (plagioclase and silica-rich crystals) to rise to the surface, forming the crust. This in turn led to the formation of a dense metallic core that is rich in iron, some nickel, and traces of sulfur. The inner core, with a diameter of ~480 km, is solid, while the outer core is liquid, increasing the total diameter of the core to ~660 km. Above the core is the mantle, with a thickness of approximately 1338 km, and the lunar crust. They formed when the magma ocean began to cool, and crystals sank and rose to the surface. The lunar crust is predominantly anorthosite in composition. Dark areas, known as lunar seas, are filled with solidified basalt, which is the result of past volcanic activity. According to geophysical data, the lunar crust has an average thickness of ~60 km on the near side and ~100 km on the far side. The upper part of the lunar crust is 35–40 km thick and is less dense. The presence of a partially molten layer in the lower mantle serves as a physical mechanism for the generation of magma at depth. Its uplift caused the eruption of marine basalts onto the lunar surface, especially where the crust is thinner. Studies show that enrichment with radioactive elements can keep the upper mantle hotter, even billions of years after the Moon's formation. The surface of the Moon is characterized by two main types of terrain, which contrast sharply in color, height, and age: light, high-altitude, composed mainly of anorthosite rocks rich in aluminum and calcium, the continents (Terrae), and dark lowlands - Maria. The lunar continents are old, heavily cratered highlands; they occupy up to 83% of the entire surface of the Moon and are mostly located on the far side. The lunar Maria are large, dark, relatively flat lowlands; they occupy about 17% of the surface, mostly on the visible side. The evolution of the lunar relief is related to its geological history, which is divided into several geological epochs: the Pre-Nectarian period (up to 3.92 billion years ago), when a magma ocean existed and intensive accretion of material and formation of the primary crust occurred; the Nectarian period (3.92–3.85 billion years ago) was a period of intensive bombardment, during which most of the large impact basins were formed; the Imbrian period (3.85–3.2 billion years ago) is a period when, after the late intensive bombardment, a period of massive eruptions of basaltic lavas began, which filled the low-lying impact basins, forming dark seas; during the Eratosthenian period (3.2–1.1 billion years ago), volcanic activity decreased significantly, and during the Copernican period (1.1 billion years ago–today) the intensity of meteorite impacts also decreased. Therefore, during rare impact events, craters formed during this period are relatively “fresh”, with bright ray systems. The Moon was dominated by low-viscosity effusive eruptions, which led to the formation of vast marine plains. However, explosive eruptions also occurred, which produced pyroclastic deposits. The low gravity and lack of an atmosphere contributed to the dispersion of pyroclastic material over long distances. In addition to the seas, volcanism also created a variety of smaller morphological features that shape the Moon's modern terrain. These include lava tubes, which are tunnels formed by the cooling of the outer part of a lava flow; furrows (rilles) are channel-like structures formed by lava flows; wrinkle ridges are tectonic features that form in areas of compression, often in the center of basins, where the surface bends around features under the lava, such as old impact craters; lunar domes and cones are small volcanic formations, usually composed of basalt; lunar pyroclastic deposits are low-albedo areas composed of fine-grained material formed by explosive volcanic eruptions; irregular mare patches are volcanic features whose absence of craters and clear appearance indicate that they formed less than 100 million years ago. That is, volcanism played a central role in shaping the Moon's surface and its current geological state. Volcanism in the Solar System is divided into two main types: silicate and cryovolcanism. Silicate volcanism involves the eruption of molten silicate rock, which is the predominant type of volcanism on rocky bodies such as Earth, the Moon, Mars, and Venus. Mafic (magnesium- and iron-rich) lavas, typically basaltic, are common and tend to create broad, gently sloping shield volcanoes and large lava plains. In contrast, cryovolcanism involves the extrusion of liquids and vapors composed of volatile compounds such as water, ammonia, and methane. These substances are frozen on the surfaces of icy bodies in the outer Solar System but may exist there in liquid or slushy form beneath the surface. The Moon therefore plays a unique and invaluable role in understanding the early history of the Solar System.