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Mare Imbrium

Mare Imbrium is a vast basaltic plain on the near side of the Moon, filling the Imbrium impact basin, one of the largest such features on the lunar surface with a diameter of approximately 1,160 kilometers centered at 33° N, 16° W.^[1]^[2] Formed by the solidification of extensive lava flows that flooded the basin, it covers an area of about 1,145 kilometers in diameter and is characterized by its dark, smooth appearance due to the fine-grained igneous rock.^[2]^[3] The Imbrium Basin itself resulted from a massive meteoroid impact roughly 3.85 billion years ago during the Late Heavy Bombardment period, excavating a multi-ring structure surrounded by the prominent Montes Apenninus mountain range, which rises up to 4.6 kilometers at peaks like Mount Hadley.^[1]^[3] Approximately 500 to 600 million years later, around 3.3 billion years ago, volcanic activity from the lunar mantle erupted basaltic lavas that filled the basin floor, creating the mare's layered terrain marked by wrinkle ridges, rilles, and secondary craters.^[3]^[4] This volcanism records a key phase in the Moon's thermal evolution, with the basalts exhibiting diverse compositions from high-titanium to low-titanium varieties.^[4] Notable features within and around Mare Imbrium include the flooded crater Archimedes to the east, the prominent Copernicus crater to the southwest, and the Sinus Iridum bay along the northern rim.^[5]^[6] The region has been a focal point for lunar exploration, with NASA's Apollo 15 mission landing in 1971 near Hadley Rille on the southeastern edge to sample the mare basalts and study the basin's geology, the Soviet Luna 17 mission in 1970 deploying the Lunokhod 1 rover directly onto the mare surface, and China's Chang'e-3 mission in 2013 landing in the northern part of the mare to deploy the Yutu rover for surface and composition analysis.^[4]^[7]^[8] Modern observations from the Lunar Reconnaissance Orbiter continue to reveal details of its impact ejecta, recent small craters, and mascon gravity anomalies.^[9]^[10]

Location and Geography

Coordinates and Extent

Mare Imbrium is situated on the Moon's near side, with its central coordinates at approximately 34.7°N 14.9°W.^[2] The feature spans a diameter of about 1,145 km, making it one of the largest lunar maria.^[2] As the basaltic fill within the Imbrium Basin, it occupies a substantial portion of the basin's interior.^[11] The mare's boundaries are sharply defined by major mountain ranges that form part of the basin's multi-ring structure. To the southeast lies the Montes Apenninus, a rugged chain rising up to 5.5 km above the mare floor and marking the transition to the Fra Mauro highlands. The northeastern edge is bordered by the Montes Caucasus, while the northwestern margin is delineated by the Montes Alpes, both of which extend as arcuate scarps from the basin's impact-related tectonics.^[12] These ranges enclose the mare's relatively flat, dark plains, with the overall extent reaching from about 15°N to 51°N in latitude and spanning longitudes from 8°E to 38°W.^[2] Mare Imbrium is separated from adjacent maria, highlighting its role in the near-side volcanic province. It is separated from Mare Serenitatis to the east by the Montes Apenninus and Montes Caucasus highlands. To the west and southwest, it merges with the expansive Oceanus Procellarum, forming a continuous lowland terrain that dominates the northwestern quadrant of the near side.^[12] This positioning highlights Mare Imbrium's integration into the broader network of lunar basaltic plains.

Surrounding Terrain

The southeastern boundary of Mare Imbrium is defined by the Montes Apenninus, a prominent mountain range approximately 600 km in length formed primarily from ejecta deposited during the Imbrium basin impact event.^[13] Peaks in this range rise up to 5.5 km above the surrounding mare surface, creating a rugged escarpment that sharply delineates the mare's irregular edge. To the northeast and north, the Montes Caucasus and Montes Alpes represent segments of the basin's secondary inner rings, with peaks reaching elevations of 3-4 km and 2-3 km above the mare level, respectively, and serving as elevated rim fragments that partially enclose the basin.^[14] These ranges contribute to the mare's contoured outline by forming elevated barriers that interrupt the otherwise smooth transition to adjacent highlands. On the northwestern margin, Sinus Iridum forms a prominent embayment extending into Mare Imbrium, spanning about 200 km in width and representing the flooded floor of a pre-existing impact crater approximately 250 km in diameter.^[15] This feature is framed by the arcuate Montes Jura, with prominent headlands including Promontorium Laplace to the northeast and Promontorium Heraclides to the southwest, which mark the surviving portions of the original crater rim and influence the mare's boundary by creating a sheltered inlet.^[15] The irregular outline of Mare Imbrium is further shaped by extensive ejecta blankets from the basin-forming impact, which mantle the surrounding terrain and include radial patterns of secondary craters that cluster along the mare's periphery, enhancing the topographic contrast between the basin floor and encircling highlands.^[1]

Formation and Geology

Impact Basin Origin

The Imbrium Basin, precursor to Mare Imbrium, originated from a cataclysmic impact event approximately 3.9 billion years ago during the Late Heavy Bombardment period. This event involved a protoplanet-sized impactor, estimated at over 100 km in diameter, striking the lunar surface at velocities exceeding 10 km/s, excavating vast amounts of material and fundamentally altering the Moon's crustal structure.^[16] The impact is associated with regional tectonic and compositional features in the Procellarum KREEP Terrane,^[17] and is recognized as one of the largest basin-forming events on the Moon, contributing significantly to the planet's early bombardment history.^[17] The initial transient crater formed by this impact was exceptionally deep, reaching approximately 300 km, reflecting the immense energy release that vaporized and displaced lunar material on a planetary scale.^[18] Collapse and modification of this cavity resulted in a characteristic multi-ring structure, with the innermost ring measuring about 600 km in diameter, delineating the inner basin structure.^[18] These rings, including prominent features like the Montes Rook and Montes Apenninus, delineate the basin's radial fractures and slumped walls, providing evidence of the dynamic rebound and relaxation processes following the excavation phase. Ejecta from the Imbrium impact was distributed asymmetrically, forming extensive ray systems that blanketed surrounding highlands and extended toward antipodal regions on the lunar farside, where focused deposition created disrupted terrains and enhanced thorium concentrations.^[19] This widespread blanket, known as the Imbrium ejecta unit, forms a critical stratigraphic marker in lunar highland geology, overlying older crust and underlying later basin deposits, thus helping to sequence the Moon's impact chronology.^[20] Remote sensing data from NASA's GRAIL mission has revealed pronounced gravity anomalies associated with the Imbrium mascon, a mass concentration resulting from the impact's crustal thinning and subsequent uplift, with positive Bouguer anomalies reaching 300–400 mGal in the basin center.^[21] These anomalies, mapped at high resolution using dual spacecraft tracking, confirm the basin's deep excavation and incomplete isostatic compensation, highlighting the enduring geophysical imprint of the event.^[22]

Lava Flows and Volcanism

The volcanic filling of Mare Imbrium occurred through multiple episodes of basaltic lava extrusion, primarily via fissure eruptions that flooded the impact basin following its formation. These eruptions were part of a broader lunar magmatic event during the Imbrian period, triggered by the decompression and partial melting induced by the basin-forming impact.^[23] Lava flooding in Mare Imbrium spanned from approximately 3.9 to 2.0 billion years ago, with the main episodes concentrated between 3.8 and 3.6 Ga, and late-stage flows occurring around 3.0 to 2.0 Ga.^[23] These pulses of volcanism produced overlapping flow units, as revealed by high-resolution imagery from the Lunar Reconnaissance Orbiter (LRO), which shows distinct flow margins and superposed layers indicative of episodic emplacement.^[24] The primary source vents for these lavas were fissures associated with sinuous rilles, such as Rima Brayley in the southwestern part of the mare and rilles near Aristillus crater in the northeast, suggesting low-viscosity, channelized eruptions over long distances.^[25] Detailed mapping from Apollo orbital photography traces many flows to structurally controlled fissures, including a prominent 20-km-long vent north of Euler crater that fed extensive late-stage units.^[25] The basaltic flows exhibit an average thickness of 500–1000 m, reaching up to 1.5 km in the basin center and along the buried ring shelf, based on gravity and topography analyses.^[26] The total volume of extruded basalt is estimated at 1.3 × 10^6 km³, representing a significant portion of the nearside mare volcanism and highlighting the scale of magmatic activity in the region.^[26]

Age and Stratigraphy

The stratigraphy of Mare Imbrium reflects a complex history of impact excavation, volcanic infilling, and subsequent tectonic modification, with geological units layered in a relative chronological sequence. The oldest materials consist of highland ejecta blankets predating the formation of the Imbrium basin itself, which occurred approximately 3.9 billion years ago (Ga) during the Late Heavy Bombardment. These ejecta, derived from surrounding highlands and the basin rim, form the basal substrate upon which mare basalts were later emplaced. Overlying these are Imbrian-aged mare units (3.8–3.2 Ga), representing the initial flood basalts that filled the basin depression, followed by Eratosthenian units (3.2–1.1 Ga) that include later, thinner flows. The youngest surficial features include Copernican rays (post-1.1 Ga) from nearby impact craters, such as those emanating from Copernicus, which overprint the mare surface and indicate minimal resurfacing since their formation. Absolute ages for these units are primarily derived from crater size-frequency distribution (CSFD) analysis, a method that counts impact craters across defined counting areas and fits the data to established production and chronology functions to yield model ages. Early CSFD studies, based on Lunar Orbiter and Clementine imagery, established a broad range of 3.57–2.01 Ga for exposed mare basalts in Imbrium, with a primary peak of activity at 3.6–3.8 Ga and a secondary peak at 3.3–3.5 Ga. Higher-resolution images from the Lunar Reconnaissance Orbiter Camera (LROC) have enabled the inclusion of smaller craters (down to ~10 m diameter), refining ages for Eratosthenian flows; for instance, northeast Imbrium flows yield model ages of approximately 3.4 Ga, highlighting episodic late-stage volcanism. These methods reveal a prolonged eruptive history spanning over 1.5 billion years, with error margins typically ±0.1–0.2 Ga depending on unit exposure and image resolution. The stratigraphic sequence in Mare Imbrium begins with the pre-3.9 Ga highland ejecta, succeeded by basal low-titanium (low-Ti) mare layers emplaced in the late Imbrian period, which form the thickest foundational fill (up to several hundred meters). These are overlain by high-titanium (high-Ti) flows during the early Eratosthenian, representing a shift in mantle source composition or melting conditions. Wrinkle ridges, prominent arcuate and linear compressional features, deform and dam these upper flows, indicating post-emplacement contraction of the lunar lithosphere due to isostatic rebound and thermal cooling following basin loading. Relative ages from ridge-flow interactions constrain ridge formation to between 3.0 and 2.0 Ga in many areas, with some young ridges potentially as recent as 1.0 Ga. This layered record underscores evidence for extended volcanism in Mare Imbrium, with activity persisting 500 million years longer than in older basins like Humorum and over 1 billion years beyond that in younger maria such as Tranquillitatis, implying regionally variable mantle thermal evolution and prolonged partial melting beneath the basin. The contrast highlights Imbrium's role as a key site for late lunar magmatic processes, distinct from the more concentrated eruptive episodes elsewhere on the nearside.

Physical Characteristics

Topography and Morphology

Mare Imbrium exhibits a relatively flat topography, with its surface averaging approximately 1.6 km below the lunar datum, forming a broad basin floor characterized by gentle slopes of less than 1° that facilitate the preservation of volcanic features.^[27] This low-lying plain spans over 1,100 km in diameter and reflects the infilling of the ancient impact basin by successive layers of basaltic lava, resulting in a subdued relief compared to surrounding highlands.^[11]^[24] Prominent structural features include wrinkle ridges, such as those in the Rimae Imbrium system, which rise up to 300 m in height and formed due to compressive stresses during the cooling and contraction of the mare basalts. These arcuate ridges, often several kilometers long and tens to hundreds of meters wide, trace radial patterns influenced by the underlying basin structure and are most evident in the southern and eastern portions of the mare. Additionally, ghost craters—pre-existing impact structures partially buried by lava flows—dot the surface, with examples like Wallace (26 km diameter) and Lambert displaying only their raised rims protruding through the basaltic fill, providing evidence of the mare's volcanic resurfacing.^[28]^[29]^[30] Sinuous rilles, such as Rima Heraclides near Promontorium Heraclides, incise the mare floor to depths of 100-200 m and widths up to 1 km, representing erosional channels carved by turbulent ancient lava flows that meandered across the terrain. These features, often branching and leveed, extend for tens of kilometers and highlight the dynamic nature of early volcanic activity in the region. The mare also bears the imprint of impact modifications, including secondary craters ejected from the Imbrium basin-forming event itself, with densities of approximately 10-20 craters per km² in the 1-5 km diameter range contributing to the textured surface overlaying the smoother volcanic plains.^[31]^[32]^[33]

Composition and Mineralogy

Mare Imbrium basalts exhibit a bulk composition typical of lunar mare rocks, characterized by relatively low silica content of 40-50 wt% SiO₂, elevated iron oxide levels of 15-20 wt% FeO, and variable titanium dioxide ranging from 1-7 wt% TiO₂ across different flows.^[34]^[35] These compositions reflect derivation from partial melting of the lunar mantle, with higher FeO contributing to the dense, iron-rich nature of the lavas that filled the basin.^[36] The primary minerals in these basalts include pyroxene as the dominant phase at approximately 60 vol%, plagioclase feldspar around 25 vol%, and olivine comprising about 10 vol%, with ilmenite more abundant in high-Ti units where it can reach up to 20 vol%.^[37]^[36] This mineral assemblage indicates crystallization from mafic melts under low-pressure conditions, with pyroxene and olivine reflecting the mantle source's olivine-pyroxene dominated peridotite composition.^[38] Spectral analyses from the Clementine mission and the Moon Mineralogy Mapper (M³) reveal characteristic absorption bands at ~1000 nm (due to pyroxene and olivine) and ~2000 nm (due to plagioclase), with overall hues ranging from blue in fresher, less weathered areas to red in mature regolith influenced by space weathering.^[39] Space weathering, involving micrometeorite impacts and solar wind implantation, darkens and reddens the spectra over time, masking fresh mineral signatures and creating color contrasts observable in multispectral imagery.^[40] Compositional variations within Mare Imbrium include high-Ti units (up to 7 wt% TiO₂) in the northeast, associated with olivine-rich basalts, contrasted with low-Ti units (1-3 wt% TiO₂) in the southwest, which are more pyroxene-dominated.^[35] These differences are attributed to heterogeneity in the underlying lunar mantle, with distinct source regions influenced by varying degrees of KREEP enrichment and partial melting depths.

Nomenclature

Etymology

The name Mare Imbrium derives from Latin, where mare means "sea" and imbrium is the genitive plural of imber, translating to "of the rains" or "of the showers," thus rendering the full name as "Sea of Rains" or "Sea of Showers."^[41] The term was coined by the Italian Jesuit astronomer Giovanni Battista Riccioli in his 1651 work Almagestum Novum, a comprehensive astronomical treatise that included a detailed lunar map prepared with the assistance of Francesco Maria Grimaldi.^[42] Riccioli's system systematically named lunar features, assigning poetic, descriptive labels to the dark basaltic plains known as maria, drawing from classical languages to create a standardized nomenclature that largely persists today.^[43] This naming reflects the 17th-century perception of lunar maria as vast bodies of water resembling Earth's oceans and seas, a view influenced by telescopic observations that highlighted their smooth, dark expanses amid rugged terrain.^[44] In English, Mare Imbrium is pronounced /ˈmɑːreɪ ˈɪmbriəm/.^[45]

Historical Designations

Prior to the invention of the telescope in the early 17th century, ancient cultures such as the Greeks and Chinese observed the Moon as a uniform disk with indistinct darker patches, but these features, including what would later be identified as Mare Imbrium, were not distinguished or named individually.^[46] In 1647, Polish astronomer Johannes Hevelius published Selenographia, the first comprehensive lunar atlas, in which he designated the large dark plain now known as Mare Imbrium as Mare Mediterraneum (Mediterranean Sea), drawing on classical geographic analogies for its expansive appearance.^[11] Four years later, in 1651, Italian Jesuit astronomer Giovanni Battista Riccioli introduced his influential nomenclature system in Almagestum Novum, renaming the feature Mare Imbrium (Sea of Showers) to evoke meteorological phenomena, a designation that has endured due to its poetic and descriptive quality.^[47] Riccioli's system, which emphasized thematic naming for lunar maria, was mapped with the assistance of Francesco Maria Grimaldi and became the basis for subsequent selenography.^[11] During the 19th century, German astronomers Wilhelm Beer and Johann Heinrich Mädler produced Mappa Selenographica between 1834 and 1836, a highly detailed lunar map at a scale of approximately 1:3.2 million that refined positional accuracy using micrometric measurements and retained Riccioli's name for Mare Imbrium while cataloging surrounding features with unprecedented precision.^[48] This map, based on observations from Beer's private observatory, marked a shift toward systematic coordinate-based mapping and influenced later works until photographic selenography emerged. In 1935, the International Astronomical Union (IAU) formalized lunar nomenclature through the publication of Named Lunar Formations by Mary Blagg and Karl Müller, adopting Riccioli's designations—including Mare Imbrium—as standard for 681 principal features to resolve inconsistencies in historical maps.^[49] Associated features, such as the prominent crater Archimedes along its southeastern margin, were named by Riccioli after the ancient Greek mathematician, while smaller subsidiary craters and ridges received IAU approvals post-1970 to accommodate new imaging data without altering the mare's core name.^[2]

Exploration History

Early Observations

In 1610, Galileo Galilei turned his newly constructed telescope toward the Moon and observed its surface as consisting of brighter, rugged highlands interspersed with darker, smoother regions that he likened to terrestrial seas and continents, though he did not identify or name specific features such as Mare Imbrium. These initial telescopic views marked a departure from the previously held notion of the Moon as a perfect, ethereal sphere, revealing instead a world-like body with varied topography. By 1651, Giovanni Battista Riccioli, an Italian Jesuit astronomer, conducted more detailed telescopic studies and mapped the lunar surface in his comprehensive work Almagestum Novum, where he designated the prominent dark plain now known as Mare Imbrium as "Mare Imbrium" (Sea of Showers) due to its expansive, sea-like appearance, surrounded by prominent mountain ranges such as the Montes Alpes and Montes Apenninus.^[50] Riccioli's nomenclature and detailed sketches established a foundational system for lunar cartography, emphasizing the region's basin-like structure and adjacent elevated terrains, which he interpreted as ancient watery features amid mountainous barriers.^[50] In the 19th century, telescopic observations advanced with efforts to analyze the Moon's composition and origins. Angelo Secchi, director of the Vatican Observatory from 1849, conducted extensive visual and early photographic studies of the lunar surface in the 1850s, producing a precise micrometrical map of the crater Copernicus and capturing some of the first wet-collodion photographs of the Moon, which highlighted features like the dark maria including Imbrium as potentially volcanic in nature due to their smooth, basaltic-like expanses.^[51] Secchi's work suggested a volcanic history for lunar formations, aligning with prevailing theories that attributed the maria's dark patches to ancient lava flows rather than impacts.^[52] Photographic techniques further refined lunar mapping between 1896 and 1910 through the efforts of Maurice Loewy and Pierre Puiseux at the Paris Observatory, who produced the Atlas Photographique de la Lune, a landmark series of 80 high-resolution plates derived from thousands of telescopic exposures, providing unprecedented detail of Mare Imbrium's irregular basin edges, internal wrinkle ridges, and surrounding ejecta blankets.^[53] This atlas surpassed earlier drawings by offering scalable, objective images that facilitated quantitative measurements of the mare's dimensions and morphology, approximately 1,145 km in diameter, and supported ongoing selenographic studies.^[53] Early selenographic debates centered on the origins of lunar features like Mare Imbrium, with volcanic theories dominating from the 17th century onward, positing that the dark maria resulted from extensive lava flooding in impact basins, as inferred from visual similarities to Earth's volcanic plains.^[52] In contrast, alternative impact hypotheses, first experimentally tested by dropping projectiles onto soft surfaces to mimic crater rims, gained traction in the late 19th century, challenging the volcanic model by proposing that basins like Imbrium formed from large meteorite collisions followed by secondary volcanism.^[52] These discussions, rooted in pre-spacecraft observations, underscored the transition from qualitative descriptions to empirical testing in understanding the Moon's geology.^[54]

Luna 17 Mission

The Luna 17 mission, launched by the Soviet Union on November 10, 1970, at 14:44 UTC from the Baikonur Cosmodrome aboard a Proton-K rocket, marked a significant advancement in robotic lunar exploration.^[55] The spacecraft entered lunar orbit on November 15 and achieved a soft landing on November 17 at 03:47 UTC at coordinates 38.24°N, 35.00°W in the northwestern portion of Mare Imbrium, approximately 75 km southeast of Promontorium Heraclides.^[56] This site was selected for its smooth basaltic plains, minimizing risks to the deployed rover and enabling extensive surface operations.^[57] Upon landing, Luna 17 deployed Lunokhod 1, the first successful robotic lunar rover, which unfolded its solar panels and began traversing the mare surface. The rover operated for 11 lunar days, spanning 322 Earth days, with the last communication on September 14, 1971, and the mission officially ending on October 4, 1971, covering a total distance of 10.54 km across varied terrain including craters and ridges.^[58] Equipped with two television cameras, Lunokhod 1 captured over 20,000 images, including more than 200 panoramic views that provided the first color imagery of the lunar surface, revealing details of the regolith's texture and the mare's subdued topography.^[59] Additional instruments included a cone penetrometer for measuring soil mechanical properties, an X-ray fluorescence spectrometer for chemical analysis, and a radiation detector, allowing in-situ examination of the local environment. Scientific findings from Lunokhod 1 focused on regolith characteristics, with penetrometer data indicating average densities of 1.5–1.8 g/cm³ and bearing strengths suitable for rover mobility, consistent with fine-grained, cohesive basaltic soil in the mare setting.^[60] The lander's seismometer recorded passive seismic events, contributing initial data on lunar interior activity, while combined analyses suggested a mare basalt layer thickness of approximately 1 km in the region, informing models of volcanic infill.^[61] Soil analyses via spectrometry detected elevated titanium and iron content, aligning with Imbrium's highland-influenced compositions. These results demonstrated effective rover-based remote sensing and paved the way for subsequent automated missions by validating long-duration mobility and in-situ experimentation.^[57]

Apollo 15 Mission

Apollo 15, launched on July 26, 1971, from Kennedy Space Center, achieved a successful lunar landing on July 30, 1971, at 6:16 p.m. EDT in the Hadley-Apennine region near the southeastern edge of Mare Imbrium, at coordinates 26°06'04" N, 3°39'10" E, adjacent to Hadley Rille.^[62] The mission's landing site was selected for its diverse geological features, including the rille, mare plains, and the Apennine Mountains, to facilitate comprehensive study of lunar volcanism and crustal evolution.^[63] Astronauts David R. Scott (commander) and James B. Irwin (lunar module pilot) conducted three extravehicular activities (EVAs) totaling 18 hours and 37 minutes, traversing approximately 27 kilometers across the lunar surface using the first Lunar Roving Vehicle (LRV), which extended their exploration range significantly beyond previous missions.^[63] During these EVAs, they collected 77 kilograms of lunar samples, including notable green glass spherules from the regolith, which provided insights into ancient volcanic fire-fountaining events on the Moon.^[64]^[65] The LRV, a battery-powered rover capable of speeds up to 13 km/h, enabled efficient sample collection and geological mapping at stations along Hadley Rille and nearby craters.^[66] The mission deployed the Apollo Lunar Surface Experiments Package (ALSEP), including the Heat Flow Experiment, which measured subsurface temperatures via probes inserted up to 2.1 meters deep, yielding a heat flow value of 0.021 W/m² at the site and indicating relatively low internal heat production in the lunar crust.^[67] Key discoveries included the "Genesis Rock" (sample 15415), a 4.1 billion-year-old anorthosite fragment that confirmed the existence of an ancient, plagioclase-rich lunar crust formed shortly after the Moon's accretion.^[68]^[4] Observations of Hadley Rille's sinuous morphology, cross-sections, and basaltic flows supported its interpretation as a collapsed lava channel formed during Imbrium-era volcanism, linking mare basalts to rille development.^[69] These findings, bolstered by brief integration of prior robotic data from Luna 16, advanced understanding of Mare Imbrium's stratigraphic history.^[70]

Chang'e-3 Mission

The Chang'e-3 mission, part of China's Lunar Exploration Program, launched on December 1, 2013, from the Xichang Satellite Launch Center aboard a Long March 3B rocket.^[71] The spacecraft, consisting of a lander and the Yutu rover, entered lunar orbit and successfully touched down on December 14, 2013, at coordinates 44.12°N, 19.51°W in the northeastern region of Mare Imbrium, near the rim of a 450-meter-diameter impact crater known as Zi Wei.^[72] This site was selected for its relatively flat terrain and scientific interest in unexplored basaltic plains, marking China's first soft lunar landing and the first robotic mission to the interior of Mare Imbrium.^[73] Upon landing, the Yutu rover, weighing 140 kg and equipped with solar panels for mobility during lunar daylight, separated from the lander and traversed approximately 114 meters across the surface before losing mobility in January 2014 due to mechanical issues. It continued limited stationary science over 31 lunar days until ceasing operations in August 2016, having exceeded its planned three-month lifespan.^[74] The rover's Alpha Particle X-ray Spectrometer (APXS) conducted in-situ analyses of the regolith, revealing a high-titanium basalt composition with TiO₂ content averaging about 5.85 wt%, higher than that observed in nearby Apollo 15 samples from the mare's edge.^[73] Complementing this, the rover's Lunar Penetrating Radar (LPR) operated at frequencies of 60 MHz and 500 MHz to probe subsurface structures, identifying a thin regolith layer (4–6 meters thick) overlying multiple basalt flows, with the underlying mare basalt unit estimated to exceed 300 meters in thickness based on layered reflections indicating successive volcanic emplacements.^[75] These findings provided the first ground-based confirmation of the multilayered volcanic history in this part of Mare Imbrium. Key instruments on Yutu included the Visible and Near-Infrared Imaging Spectrometer (VNIS), which spanned 0.45–1.40 μm to map mineral compositions and search for potential volatile signatures in the regolith, detecting olivine and pyroxene indicative of mafic basalts.^[76] The Panoramic Camera (PCAM) captured 3D images of the surroundings, documenting young lava flows and impact features that highlighted the site's relatively recent volcanic activity, estimated at around 3.2 billion years old.^[77] The lander itself carried additional payloads, such as a terrain camera for surface mapping, contributing to contextual imaging of the northeast mare. The lander, designed for one year of operation, far outlasted expectations, remaining active for over a decade and providing ongoing environmental and particle flux data until at least 2020, with reports indicating functionality as of 2025.^[78] Together, these efforts yielded the inaugural in-situ dataset from Mare Imbrium's interior, advancing understanding of its basaltic volcanism and regolith evolution without reliance on prior Apollo-era samples from the mare's margins.^[79]

Meteor Impact Events

One of the most significant observed meteor impact events in Mare Imbrium occurred on March 17, 2013, when a meteoroid roughly 1 meter in diameter collided with the lunar surface near 21°N, 24°W. The impact generated a magnitude-4 flash, the brightest recorded by NASA's monitoring telescopes at the time, and was detected by the agency's Meteoroid Environment Office using a 0.6-meter telescope in El Leoncito, Argentina.^[80] ^[81] Follow-up analysis using Lunar Reconnaissance Orbiter (LRO) images taken before and after the event confirmed the formation of an 18-meter-wide crater, surrounded by bright ejecta rays extending up to 30 kilometers, highlighting the explosive energy of the collision at approximately 56,000 km/h.^[82] Ongoing monitoring of lunar meteor impacts, including those in Mare Imbrium, is conducted through dedicated programs such as NASA's Lunar Impact Monitoring Program, which has operated since 2005, and the European Space Agency's NELIOTA (NEO Lunar Impacts and Optical TrAnsients), initiated in 2017 with a 1.2-meter telescope at the Kryoneri Observatory in Greece.^[83] ^[84] These efforts detect impact flashes on the Moon's night side, estimating approximately 100 detectable impacts per year across the entire lunar surface, primarily from meteoroids in the gram-to-kilogram mass range.^[85] NELIOTA alone has validated approximately 192 impact events as of 2025, contributing to a global catalog that aids in characterizing the meteoroid environment and potential hazards to lunar missions.^[84] The 2013 impact in Mare Imbrium has enabled detailed studies of fresh ejecta using LRO's Narrow Angle Camera, revealing key aspects of regolith dynamics such as excavation depths, particle size distributions, and ballistic trajectories that redistribute basaltic material across the mare plains. Modern observations from LRO continue to reveal details of impact ejecta in the region.^[82] ^[10] These observations demonstrate how impacts garden the regolith, mixing upper layers and exposing subsurface compositions without significant volatile content.^[61] Notably, spectral analysis of the ejecta showed no evidence of water ice, consistent with the anhydrous nature of equatorial mare regolith as confirmed by prior orbital missions like Lunar Prospector.^[86] As of 2025, no major new meteor impact events comparable to the 2013 incident have been reported in Mare Imbrium by NELIOTA or NASA monitoring, though smaller flashes continue to be detected globally.^[84] LRO's repeated imaging has documented ongoing formation of small craters (less than 10 meters) throughout the Moon, including in mare regions, underscoring the persistent meteoroid flux shaping the lunar surface.

References

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Features larger than 300 kilometers in diameter are termed impact basins. More than 40 such basins have been identified on the Moon.
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The basalts in Mare Imbrium formed about 3.3 billion years ago, 600 million years after the Imbrium impact basin formed.
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Mare Imbrium, 32.8°N/15.6°W · 1123 km ; Mare Serenitatis, 28.0°N/17.5°E · 707 km ; Mare Vaporum, 13.3°N/3.6°E · 245 km ; Sinus Aestuum, 10.9°N/8.8°W · 290 km.
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Imbrium, Mare - The Moon
Apr 16, 2018 · Depth data from Kurt Fisher database · Mare area of 1,130,000 km^2 according to measurements by Jim Whitford-Stark. · "Herringbone" ridges south ...Missing: authoritative | Show results with:authoritative<|control11|><|separator|>
[12]
Apollo 15 - Day 4: Lunar Orbit - NASA
Dec 29, 2018 · Mare Imbruim consists of the layers of basalt solidified from vast quantities of lava that poured out from the Moon's interior to fill the ...
[13]
Moon Map for Southern Hemisphere | Resources
Apennine Mountains (Montes Apenninus) The most spectacular of the Moon's mountain ranges stretches for 600 km along the southeast rim of the Imbrium Basin. Its ...Missing: length | Show results with:length
[14]
[PDF] Stratigraphy and Chronology of the Moon's Crust
Schaeffer and Husain (1974) place the age of the Fra. Mauro Formation at the beginning of the Imbrian at 3.95 +0.05 aeons. The top of the Imbrian System is the ...<|control11|><|separator|>
[15]
[PDF] department of the interior - united states geological survey
completely covered by mare material. Montes Alpes and Montes. Caucasus form the second and third rings, respectively. Superposed on the rugged pre-Imbrian ...
[16]
(LAC-24) Geologic map of the Sinus Iridum quadrangle of the moon
Sinus Iridum embays a simpler and smaller structure, a crater 250 km in diameter (herein referred to as the Iridum crater) whose partly exposed rim crest is ...Missing: size | Show results with:size
[17]
Asteroid that formed Moon's Imbrium Basin may have been ...
Jul 20, 2016 · “We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet,” said Pete Schultz, ...Missing: age Procellarum-
[18]
[PDF] The materials of the lunar Procellarum KREEP Terrane
A succession of basin-sized impacts occurred within the Procellarum KREEP Terrane [DeHon, 1979;. Spudis, 1993]; these would have renewed topographic roughness.
[19]
[PDF] METEORITE IMPACTS, CRATERS AND MULTI-RING BASINS
There is an Inner Rook mountain ring with a diameter of 480 km and an Inner Basin Scarp with a diameter of 320 km which borders the inner mare basalt fill (see ...
[20]
Origin of strong lunar magnetic anomalies: Further mapping and ...
Apr 12, 2013 · The area near the Imbrium antipode is characterized by enhanced surface thorium abundances, which may be a consequence of antipodal deposition ...
[21]
The Lunar Cratering Chronology - GeoScienceWorld
Dec 1, 2023 · For example, using the ejecta deposits of impact craters as stratigraphic marker horizons similar to volcanic ash (bentonite) beds on Earth ...
[22]
3‐D Density Structure of the Lunar Mascon Basins Revealed by a ...
Apr 26, 2021 · The positive high-density anomalies vary from 250 kg/m3 beneath the Imbrium to more than 400 kg/m3 beneath the Orientale and correspond well to ...
[23]
Lunar impact basins revealed by Gravity Recovery and Interior ...
Oct 30, 2015 · GRAIL gravity data confirm the existence of 16 additional basins that lack confidently measurable topographic rings but that have Bouguer ...Lunar Impact Basins Revealed... · Results · Gravity And Basin Morphology
[24]
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JE005041
[25]
Investigating the stratigraphy of Mare Imbrium flow emplacement ...
Jul 30, 2016 · If we follow the same calculation for crater counts down to D = 200 m, those surface areas would only need to be 2040 km2 and 560 km2, ...
[26]
Lava flows in Mare Imbrium - Geologic evaluation from Apollo orbital ...
NTRS - NASA Technical Reports Server These materials cover an area of 200,000 sq km and have a volume of perhaps 40,000 cu km. The vent source of the youngest ...Missing: km2 | Show results with:km2
[27]
A new technique for estimating the thickness of mare basalts in ...
Jun 16, 2009 · We estimate mare thickness values in the Imbrium Basin by analyzing ejecta from large (>10 km diameter) impact craters that penetrate (or failed to penetrate) ...
[28]
Analysis and mapping of lunar wrinkle ridges (LWRs ... - Frontiers
Oct 5, 2023 · The height of the basal arch and the superposed ridge might differ by up to 300 m. Typically, the basal arch is 500 m in height and the ...
[29]
Thickness of Lunar Mare Basalts: New Results Based on Modeling ...
Aug 27, 2019 · Partially buried craters on the Moon are those craters whose distal ejecta are covered by lava flows and where the crater rim crest still ...
[30]
Ghosts on the Moon at Halloween - Astronomy Now
Oct 31, 2014 · A nicely-formed little ghost crater called Wallace (26 kilometres across) can be clearly seen in Mare Imbrium around 100 kilometres north of ...
[31]
Lunar Rilles - The Moon
Apr 16, 2018 · - Rima Heraclides (the pronounced short rille and adjacent shallow sinuous rille just north of Promontorium Heraclides). http://bit.ly ...
[32]
The Origin of Sinuous Rilles - NASA ADS
... Mare Imbrium. The lunar canyon is about 1 to 1~ km wide, 300 m deep and 130 km long. It begins in a narrow, elongated V-shaped cleft, runs parallel to the ...
[33]
[PDF] MARE IMBRIUM, A REVISED APPROACH. L. R. Ostrach1,2 and ...
Results: From the crater measurements in Mare Imbrium, the absolute model age (AMA) is 3.3 ± 0.05 Ga for the spectrally red unit (~15–18 wt% FeO, ~2–5 wt% TiO2 ...
[34]
[PDF] Lunar Rocks - Lunar sourcebook : a user's guide to the Moon
and Properties of Mare Basalts Like terrestrial basalts, lunar basalts are low in silica (<54% SiO2). Most other lunar rocks, however, are also low in silica. ...
[35]
[PDF] Lunar High Alumina Basalts in Mare Imbrium - Semantic Scholar
Jun 6, 2024 · The results show that the oxide abundance range of Mare Imbrium HA basalts (Al2O3: 11.1–17.6 wt%, TiO2: 0–9 wt%, FeO: 10–22 wt%) is wider than ...
[36]
Volcanic history of the Imbrium basin: A close-up view from the lunar ...
We report the surface exploration by the lunar rover Yutu that landed on the young lava flow in the northeastern part of the Mare Imbrium.
[37]
How do we know that it is a rock from the moon? | Some Meteorite ...
Mare basalts are composed mainly, 50-65%, of pyroxene, but they all also contain 27-45% plagioclase, up to 20% ilmenite and related Ti-rich minerals, and 0-25% ...Missing: Imbrium | Show results with:Imbrium
[38]
[PDF] Chapter 5: Lunar Minerals
5.1. The silicate minerals, especially pyroxene, plagioclase feldspar, and olivine, are the most abundant minerals in rocks of the lunar crust and mantle.Missing: Imbrium | Show results with:Imbrium
[39]
Newer views of the Moon: Comparing spectra from Clementine and ...
Jun 30, 2011 · The Moon Mineralogy Mapper (M3) provided the first global hyperspectral data of the lunar surface in 85 bands from 460 to 2980 nm.
[40]
Lava flows in Mare Imbrium - an evaluation of anomalously low ...
Surface-area distribution of relative blue-red spectral reflectivity for the Imbrian red and blue mare surfaces within Mare Imbrium. Areas scanned shown in ...Missing: weathering | Show results with:weathering
[41]
Seven Seas - NASA Science
Nov 12, 2012 · On the Moon, areas of smooth plains are called "maria," plural of the Latin word "mare," for "sea." For example, Mare Imbrium is the Sea of ...<|control11|><|separator|>
[42]
Rain - Etymology, Origin & Meaning
from stem of Latin imbricare "to cover with tiles," from imbricem (nominative imbrex) "curved roof tile used to draw off rain...," from imber (genitive imbris) ...Missing: imbrium mythology
[43]
1651. Giovanni Riccioli's Almagestum novum - OBSPM
By proposing a new lunar nomenclature, Riccioli reveals a certain idea of the world. Giovanni Riccioli, Almagestum novum, 1651. Crédits : ETH-Bibliothek ...
[44]
Going to the Moon: Early Cartography of the Lunar Surface
Mar 24, 2020 · Riccioli named many of the moon's features including the Sea of Tranquility (Mare Tranquillitatis), the site for the first manned lunar landing ...
[45]
The History of the Moon's Seas - WIRED
Jul 9, 2008 · Responsible for the names was Giambattista Riccioli, a 17th-century Jesuit astronomer who hoped to replace the Copernican model of the universe ...
[46]
MARE IMBRIUM Definition & Meaning - Dictionary.com
Mare Imbrium, or “Sea of Rains,” might be as much as 200 million years older than scientists once thought.
[47]
Mare | Lunar Feature, Origin, Characteristics & Types - Britannica
Oct 22, 2025 · surface area, 37,900,000 km · 510,000,000 km2 (land area, 149,000,000 km2) ; mass, 0.0735 × 1024 kg, 5.976 × 1024 kg ; mean density, 3.34 g/cm ...
[48]
[PDF] v - USGS Publications Warehouse
Mare Imbrium, the large, round basin in this telescopic photograph, is about 750 miles in diameter. This feature appears to be the result of a giant impact ...
[49]
11. Beer, Wilhelm and Mädler, Johann Heinrich - Linda Hall Library
Because Lohrmann's map did not appear in full until 1878, the Beer and Mädler map has the honor of being the first large-scale moon map to be based on precise ...
[50]
How objects are named today | Astronomy.com
Aug 29, 2005 · This committee's 1935 report, Named Lunar Formations, by Mary Blagg and Karl Müller, was the first systematic listing of lunar nomenclature.
[51]
05. Riccioli, Giovanni Battista - Linda Hall Library
The Riccioli moon map is historically of great importance, since it provided the basis for the system of lunar nomenclature still in use.Missing: Imbrium | Show results with:Imbrium
[52]
Scientist of the Day - Angelo Secchi, Jesuit Italian Astronomer
Jun 28, 2019 · Angelo Secchi, an Italian astronomer, was born June 28, 1818. Secchi was a Jesuit and spent most of his life with the Observatory of the Roman College in Rome.Missing: lunar volcanic
[53]
Scientific Knowledge of the Moon, 1609 to 1969 - MDPI
Dec 21, 2018 · He compared possible impact and volcanic origins by dropping balls onto wet clay, and by boiling alabaster; in both experiments circular ...
[54]
03. Earth-based Lunar Photography - Linda Hall Library
Loewy's atlas, published between 1896 and 1904, featured 80 plates of the Moon which he had selected from 6,000 photographs that were taken by the observatory's ...Missing: 1896-1910 Mare Imbrium<|control11|><|separator|>
[55]
UNDERSTANDING THE HISTORY OF LUNAR IMPACT THEORIES
Aug 30, 2022 · His hypothesis, however, was not widely accepted, and volcanism was ... Further eroding any acceptance of Gilbert's hypotheses was the ...
[56]
USSR - Luna 17 - Orbital Focus
Luna 17 acted as transport to get the Lunokhod 1 roving vehicle onto the lunar surface. The Luna 17 descent stage was similar to Luna 16's.Missing: findings | Show results with:findings
[57]
Geologic characteristics of the Luna 17/Lunokhod 1 and Chang'E-3 ...
A LRO WAC mosaic showing the northwestern part of Mare Imbrium and Sinus Iridum with locations of the Luna 17 and Chang'E-3 landing sites indicated. Courtesy of ...Missing: launch | Show results with:launch
[58]
Geologic characteristics of the Luna 17/Lunokhod 1 and Chang'E-3 ...
The Luna 17 lander, with Lunokhod 1 onboard, landed in the northwestern part of Mare Imbrium ∼75 km SE of Promontorium Heraclides, which is a part of Montes ...Missing: launch findings
[59]
Lunokhod 1: 1st Successful Lunar Rover - Space
Dec 19, 2016 · Lunokhod 1 was the first successful rover to explore another world. It arrived on the moon on Nov. 17, 1970, upon the Luna 17 lander.Missing: details findings<|control11|><|separator|>
[60]
Cartography of the Lunokhod-1 landing site and traverse from LRO ...
Aug 6, 2025 · Lunokhod-1 transmitted over 211 high-quality panoramic images and more than 2 5,000 individual images o f the lunar surface. Data on the ...
[61]
Physical and mechanical properties of the lunar soil (a review)
Sep 12, 2014 · We consider all of the main physical and mechanical properties of the lunar soil, such as the granulometric composition, density and porosity, cohesion and ...<|control11|><|separator|>
[62]
Lunar Surface Processes | Reviews in Mineralogy and Geochemistry
Dec 1, 2023 · ... data to estimate the regolith thickness. ... They suggest that the average thickness of mare regolith is 5 m and 12 m for the highlands.Missing: findings | Show results with:findings
[63]
Apollo 15 Mission report Chapter 1 - NASA
The landing point was 26 degrees 6 minutes 4 seconds north latitude and 3 degrees 39 minutes 10 seconds east longitude (referenced to the Rima Hadley Lunar ...
[64]
Apollo 15: Mission Details - NASA
Jul 8, 2009 · David Scott and James Irwin flew their LM to a perfect landing at 6:16 p.m. EDT July 30, at Hadley Rille about 1,500 feet north and east of the ...
[65]
[PDF] Apollo 15 Lunar Sample Catalog Part I 15015-15299 - NASA
The collected sample mass was almost doubled , from 43 kg on Apollo 14 to 78 kg on Apollo 15 . ... collected with samples 15080 to 1508 8 , about 60 m east of the ...
[66]
Apollo 15 green glasses. - NASA Technical Reports Server (NTRS)
The samples analyzed include 28 spheres, portions of spheres, and angular fragments from soil 15101. Emerald green glasses from other soils are identical to ...Missing: spherules | Show results with:spherules
[67]
First Use of the Lunar Roving Vehicle – July 31, 1971 - NASA
Jul 31, 2019 · This week in 1971, Apollo 15 became the first mission to use the Lunar Roving Vehicle. The LRV was a lightweight, electric vehicle designed to operate in the ...
[68]
ALSEP Apollo Lunar Surface Experiments Package - NASA
Sep 30, 1977 · The results of these measurements indicate a heat flow of 21 milliwatts per square meter at the Apollo 15 landing site and of 16 milliwatts per ...
[69]
Genesis Rock - NASA Science
Sep 22, 2017 · That sample, nicknamed the Genesis Rock, sample number 15415, was an anorthosite, a piece of the moon's primordial crust.Missing: 4.1 Ga
[70]
Hadley Rille, lava tubes and mare volcanism at the Apollo 15 site
Hadley Rille appears to be a collapsed lava tube/channel, whose formation history may be more intimately related to the mare units sampled at 15 than was ...
[71]
[PDF] Apollo 15 Preliminary Science Report NASA SP-289
In richness of scientific return, the Apollo 15 voyage to the plains at Hadley compares with voyages of Darwin's H.M.S. Beagle, and those of the Endeavour ...
[72]
Chang'e-3 Moon-landing Mission - eoPortal
Dec 17, 2013 · NASA will keep track of the Chinese Yutu rover and lander when LRO (Lunar Reconnaissance Orbiter) orbits over western Mare Imbrium on Dec. 24 ...
[73]
In Situ Investigations of Dust Above the Lunar Terminator at the ...
Aug 28, 2020 · The China's Chang'E-3 (CE-3) mission was launched on 2 December 2013 and successfully landed at 44.12°N, 19.51°W in the Mare Imbrium on 14 ...<|separator|>
[74]
Correlated compositional and mineralogical investigations at the ...
Dec 22, 2015 · Here we report the composition of soil along the rim of a 450-m diameter fresh crater at the Chang′e-3 (CE-3) landing site, investigated by the Yutu rover.Missing: findings | Show results with:findings
[75]
[PDF] Nomenclature for lunar features at the Chang'e-3 landing site
Apr 27, 2017 · The successful landing of CE-3 at (19.51°W, 44.12°N) in Mare. Imbrium on December 14, 2013 marked the first return of a manmade spacecraft on ...
[76]
Data processing and initial results of Chang'e-3 lunar penetrating ...
These observations have revealed the configuration of regolith where the thickness of regolith varies from about 4 m to 6 m. In addition, one layer of lunar ...
[77]
Visible and near-infrared imaging spectrometer and its preliminary ...
... infrared Imaging Spectrometer (VNIS), one of the scientific payloads of the Chang'E 3 Yutu rover, has been developed to detect lunar surface objects and to ...Missing: instruments UV volatiles<|separator|>
[78]
(PDF) A young multilayered terrane of the northern Mare Imbrium ...
China's Chang'E-3 (CE-3) spacecraft touched down on the northern Mare Imbrium of the lunar nearside (340.49°E, 44.12°N), a region not directly sampled ...
[79]
China's Yutu rover dies on the moon - Spaceflight Now
Aug 4, 2016 · Chang'e 3 touched down near the relatively fresh Zi Wei crater on a plain overlaid with younger lava flows than regions visited by the Apollo ...
[80]
China's Chang'e 3 lunar lander still going strong after 7 ... - Space
Sep 23, 2020 · Yutu continues to make contributions long after its death, with new science results still coming from data collected by the rover. Researchers ...Missing: details | Show results with:details<|control11|><|separator|>
[81]
Regolith stratigraphy at the Chang'E‐3 landing site as seen by lunar ...
Nov 11, 2015 · The Chang'E-3 lunar penetrating radar (LPR) observations at 500 MHz reveal four major stratigraphic zones from the surface to a depth of ~20 ...
[82]
Bright Explosion on the Moon - NASA Science
May 16, 2013 · On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium," says Bill Cooke of NASA's Meteoroid Environment Office.
[83]
March 17, 2013 Lunar Impact Forms a New Crater - NASA SVS
Mar 17, 2015 · On March 17, 2013, a NASA telescope that monitors the night side of the Moon recorded a bright flash in Mare Imbrium, at about 21°N, 24°W.Missing: facts | Show results with:facts
[84]
NASA's LRO Spacecraft Finds March 17, 2013 Impact Crater and More
Mar 17, 2015 · On March 17, 2013, an object the size of a small boulder hit the surface in Mare Imbrium and exploded in a flash of light nearly 10 times as ...Missing: ejecta regolith ice
[85]
About Lunar Impact Monitoring Program - NASA
Oct 24, 2023 · Lunar impact monitoring enables measurement of meteoroids in the 10s of grams to kilograms size range which are difficult to measure with other techniques.
[86]
Lunar Impact Events (NELIOTA - Home)
We are happy to announce that the NELIOTA project is starting its third phase of lunar impact flash observations in August 2025, through a 3-year ESA contract.Missing: Mare Imbrium
[87]
Lunar Impact - NASA SVS
The impact occurred in a 700-mile-wide impact basin named Mare Imbrium. NASA astronomers have detected more than 300 strikes since they began monitoring such ...
[88]
[PDF] The Significance of Lunar Water Ice and Other Mineral Resources ...
For example, an ap- proximately 0.4 mi2 ( 1 km2) area of typical mare regolith that has a concentration of 40 ppm could be mined to a depth of approximately 3.3 ...<|control11|><|separator|>