Mare Imbrium

Mare Imbrium, or the Sea of Showers, is one of the most prominent dark regions visible on the near side of Earth's Moon. Despite the word "mare," which means sea in Latin, it is not a body of liquid water. It is a broad volcanic plain formed when basaltic lava flooded a giant impact basin created during the Moon's early history. With a diameter of approximately 1,145 kilometres, it is the second-largest lunar mare after Oceanus Procellarum and the largest mare associated with a clearly defined impact basin. The Imbrium Basin formed during the Late Heavy Bombardment, when a large protoplanet-sized body struck the Moon. Radiometric studies have placed the principal impact event at roughly 3.922 billion years ago, with an uncertainty of about 12 million years. Estimates suggest that the impactor may have been approximately 250 kilometres in diameter, although the precise dimensions remain model-dependent. The collision excavated a colossal basin, displaced material across much of the lunar near side, and generated ejecta deposits extending hundreds of kilometres from the basin rim. The basin floor subsequently experienced extensive volcanic flooding, producing the relatively smooth, dark surface now called Mare Imbrium. The mare is surrounded by several partly concentric mountain rings uplifted by the impact. The outer structures include Montes Carpatus to the south, Montes Apenninus to the southeast, and Montes Caucasus to the east. The middle ring includes Montes Alpes and Montes Archimedes, while remnants of an inner ring include Montes Recti, Montes Teneriffe, and Montes Spitzbergen. Some of these structures are submerged beneath later basalt, leaving isolated peaks such as Mons Pico and Mons La Hire. Estimates of the basalt thickness vary, commonly ranging from about two to five kilometres in the central region. The original impact cavity may have been far deeper before the basin floor rebounded and was later filled by lava. The impact also produced a large ejecta blanket and a radial pattern of grooves known as the Imbrium Sculpture. These features are interpreted as traces left by material thrown outward at shallow angles during the collision. The event may also have generated radial and concentric faults across the Moon and contributed to chaotic terrain on the opposite side of the lunar globe through the focusing of seismic energy. A substantial mass concentration, or mascon, lies beneath the central mare. It was identified through spacecraft tracking in the 1960s and later mapped in greater detail by missions including Lunar Prospector and GRAIL. Mare Imbrium has been central to lunar observation and exploration. It is visible without optical equipment and contributes to the traditional Western "Man in the Moon" pattern, where it is often perceived as the figure's right eye. Giovanni Riccioli gave it its standardized Latin name in the seventeenth century, although earlier lunar maps used different names. In 1970, the Soviet Luna 17 spacecraft landed there and deployed Lunokhod 1, the first successful robotic rover on the Moon and the first rover to operate on another celestial body. Apollo 15 landed in the southeastern Imbrium region in 1971, where astronauts explored the area near Hadley Rille and the Apennine Mountains, operated the first crewed lunar rover, and returned approximately 77 kilograms of samples, including the famous Genesis Rock. China's Chang'e 3 mission landed in Mare Imbrium in 2013 and deployed the Yutu rover, which used ground-penetrating radar to study the subsurface. The mare also hosted a bright, closely monitored lunar impact on 17 March 2013, producing an estimated crater about 18 metres across.

Mare Imbrium is the surface expression of the Imbrium Basin, one of the Moon's largest and most consequential impact structures. The basin formed during the Moon's early geological history when a large body, possibly a protoplanet from the asteroid belt, collided with the lunar surface during the Late Heavy Bombardment. Uranium-lead and other radiometric approaches have placed the event at approximately 3.922 billion years ago. The impact excavated a basin on a planetary scale, uplifted several concentric mountain rings, distributed ejecta over a broad area of the lunar near side, and generated structural disturbances that may have affected regions far from the impact site. The initial impact cavity was probably much deeper than the feature visible today. Almost immediately after excavation, the basin floor rebounded. Over subsequent geological time, basaltic magma rose through fractures and flooded the depression. The cooled basalt created a comparatively flat, dark plain that contrasts strongly with the brighter, heavily cratered lunar highlands. The thickness of the mare basalt is uncertain; gravity, seismic, radar, crater, and comparative basin studies have produced estimates generally ranging from about two to five kilometres in the central area. The basin is bordered by a system of mountain rings and related landforms. Montes Carpatus, Montes Apenninus, and Montes Caucasus form important parts of the outer rim, while Montes Alpes and other ranges mark inner structural boundaries. Some ring segments were buried by basalt, leaving isolated mountain peaks above the mare surface. The impact also generated the Imbrium Sculpture, a radial arrangement of grooves and furrows interpreted as the product of ejecta travelling outward at low angles. Geological models further associate the event with widespread radial and concentric faulting. On the opposite side of the Moon, the chaotic terrain around Van de Graaff crater has been proposed as a possible consequence of seismic waves focused by the Imbrium impact. The name Mare Imbrium belongs to the standardized nomenclature introduced by Giovanni Riccioli in 1651. Earlier lunar cartographers used other descriptions, including William Gilbert's Regio Magna Orientalis and Michael Langren's Mare Austriacum. The feature is easily visible from Earth and forms part of the familiar Western Man in the Moon pattern. Modern exploration began with the Soviet Luna 17 landing on 17 November 1970. Its Lunokhod 1 rover travelled across the mare for several months, returning engineering and scientific data and establishing a landmark in planetary exploration. Apollo 15 reached the southeastern portion of Mare Imbrium in 1971. The crew spent three days on the surface, conducted extensive extravehicular activity, used the first lunar rover operated by astronauts, and collected approximately 77 kilograms of material. Samples from the vicinity of Mons Hadley Delta included the Genesis Rock, a piece of ancient lunar crust. Mare Imbrium remained an important destination in the robotic era. On 14 December 2013, China's Chang'e 3 lander touched down about 40 kilometres south of Laplace F crater and released the Yutu rover. The mission used subsurface radar to investigate lunar soil and crustal structure, detecting at least nine distinct layers and suggesting more complex local geological development than might be inferred from the smooth surface alone. The mare has also been monitored for present-day impacts; a particularly bright collision occurred on 17 March 2013.

• 2013

  Bright impact recorded

  [1]Mare Imbriumen.wikipedia.org

  A monitored object struck Mare Imbrium on 17 March, creating a bright flash and an estimated crater approximately 18 metres in diameter.

• 2013

  Chang'e 3 lands and deploys Yutu

  [1]Mare Imbriumen.wikipedia.org

  Chang'e 3 landed in Mare Imbrium and released the Yutu rover, which conducted subsurface investigations with ground-penetrating radar.

• 1971

  Apollo 15 conducts crewed exploration

  [1]Mare Imbriumen.wikipedia.org

  Apollo 15 explored the southeastern Imbrium region, used a lunar rover, and returned approximately 77 kilograms of lunar samples.

• 1970

  Luna 17 and Lunokhod 1 reach the mare

  [1]Mare Imbriumen.wikipedia.org

  Luna 17 landed in Mare Imbrium and deployed Lunokhod 1, the first rover to operate on the Moon or any other extraterrestrial body.

• 1651

  Riccioli standardizes the name Mare Imbrium

  [1]Mare Imbriumen.wikipedia.org

  Giovanni Riccioli's lunar nomenclature gave the feature the Latin name Mare Imbrium, meaning Sea of Showers or Sea of Rains.

A major lunar geological feature and scientifically important impact basin used for astronomical observation, planetary geology, and robotic and crewed exploration.

• 2013

  Chang'e 3 targets Mare ImbriumOther

  Background

  China's first lunar soft-landing mission required a location suitable for surface mobility and geological measurements.

  Action taken

  The Chang'e 3 lander touched down in Mare Imbrium and deployed Yutu several hours later.

  Aftermath

  Radar observations revealed multiple subsurface layers and provided evidence of complex local geological processes.

  Source

• 1970

  Luna 17 selects Mare Imbrium as a rover landing siteOther

  Background

  The Soviet lunar program sought a relatively suitable surface location for deploying its first mobile extraterrestrial vehicle.

  Action taken

  Luna 17 performed a soft landing in Mare Imbrium and deployed Lunokhod 1.

  Aftermath

  Lunokhod 1 operated across the lunar surface for several months and became a landmark in robotic planetary exploration.

  Source

1. 1Mare Imbriumen.wikipedia.org