Mare Humorum

Mare Humorum is a broad lunar mare, or basalt-covered plain, located on the Moon. Its name is Latin for the “Sea of Moisture” or “Sea of Humors,” reflecting the traditional seventeenth-century practice of assigning terrestrial-sea names to the Moon’s dark plains. The feature occupies an impact basin approximately 425 kilometers across and is one of the prominent maria visible from Earth through telescopes. The basin formed in the ancient lunar crust and was later filled by extensive volcanic basalt. Geological mapping places its formation between the ages associated with the Imbrium and Nectaris Basins, indicating an approximate age of 3.9 billion years, although a precise radiometric age has not been established because Mare Humorum was not sampled by the Apollo missions. The basaltic fill is thought to be particularly thick, exceeding 3 kilometers near the center of the basin. This makes the feature important for understanding the Moon’s impact history, volcanic resurfacing, crustal structure, and gravitational evolution. A major scientific characteristic of Mare Humorum is its central mass concentration, commonly called a mascon. Doppler tracking of the five Lunar Orbiter spacecraft identified a gravitational high associated with the basin in 1968. Later lunar missions, including Lunar Prospector and the GRAIL mission, provided increasingly detailed measurements of the region’s gravity field. These observations helped refine knowledge of the basin’s subsurface structure and the distribution of its dense volcanic materials. Mare Humorum is surrounded by several notable craters and geological features. Gassendi, a large crater with a fractured floor, lies along its northern margin and was considered as a possible Apollo 17 landing site. To the south are Vitello, a floor-fractured crater, Doppelmayer, which is partly flooded by mare material, and the smaller Puiseux crater. Hippalus crater and Promontorium Kelvin are situated to the east. To the west are the Rimae Doppelmayer lava-cutting channels and Rupes Liebig, a prominent cliff near the crater Liebig. The modern name was established through the nomenclature system published by Giovanni Riccioli in 1651, whose lunar naming conventions later became standard. Earlier lunar maps used different names: Michael van Langren labeled the feature Mare Venetum in 1645, Johannes Hevelius called it Sinus Sirbonis in 1647, and Pierre Gassendi referred to it as Anticaspia. Today, Mare Humorum is treated as a named lunar geological feature rather than a commercial brand, company, or consumer offering.

Mare Humorum is a lunar geological feature whose visible surface consists primarily of dark mare basalt filling an ancient impact basin. The basin is approximately 425 kilometers in diameter and formed during the early history of the Moon, when large impacts were common. Subsequent volcanic eruptions flooded much of the depression with basaltic lava. Geological comparisons place the basin’s formation between the events associated with the Imbrium and Nectaris Basins, suggesting an age of roughly 3.9 billion years. Because no Apollo sample was collected from Mare Humorum, its age remains an estimate based on regional geological mapping rather than a directly measured sample age. The basin’s unusually thick volcanic fill is one of its defining characteristics. The basalt layer may exceed 3 kilometers in thickness at the center, indicating substantial volcanic resurfacing after the impact. The mare is therefore useful for studying how impact basins were modified by interior volcanic activity and how the Moon’s crust responded to the loading of dense basalt. Mare Humorum also became important in lunar geophysics through the discovery of a mascon, or mass concentration. In 1968, Doppler observations of the five Lunar Orbiter spacecraft revealed a gravitational high over the basin. The anomaly was subsequently examined by later lunar spacecraft, including Lunar Prospector and GRAIL, whose gravity measurements supplied more detailed information about the basin’s interior and the distribution of dense material beneath its surface. The feature has a long history of changing names in lunar cartography. Michael van Langren called it Mare Venetum on his 1645 map, while Johannes Hevelius used Sinus Sirbonis in his 1647 map. Pierre Gassendi applied the name Anticaspia, referring to the Caspian Sea association he used for another lunar mare. Giovanni Riccioli’s 1651 nomenclature system introduced Mare Humorum, the name that later became standardized in astronomical usage. Its surroundings include Gassendi crater on the northern rim, as well as Vitello, Doppelmayer, and Puiseux to the south. Hippalus crater and Promontorium Kelvin lie to the east, while Rimae Doppelmayer and Rupes Liebig are found toward the west. Gassendi was evaluated as a potential landing site for Apollo 17, although it was not selected. Mare Humorum remains a subject of planetary geology and lunar remote sensing rather than a commercial entity.

• 1968

  Central mascon identified

  [1]Mare Humorumen.wikipedia.org

  Doppler tracking of the five Lunar Orbiter spacecraft revealed a gravitational mass concentration beneath the central region of Mare Humorum.

• 1651

  Riccioli establishes the modern name

  [1]Mare Humorumen.wikipedia.org

  Giovanni Riccioli’s lunar nomenclature introduced Mare Humorum, the designation that later became standardized.

• 1647

  Hevelius uses the name Sinus Sirbonis

  [1]Mare Humorumen.wikipedia.org

  Johannes Hevelius assigned the feature the name Sinus Sirbonis on his lunar map, referencing Lake Serbonis in Egypt.

• 1645

  Mare Venetum appears on a lunar map

  [1]Mare Humorumen.wikipedia.org

  Michael van Langren labeled the feature Mare Venetum, meaning the Venetian Sea, on his early lunar map.

• Gravity structure refined by later lunar missions

  [1]Mare Humorumen.wikipedia.org

  Lunar Prospector and GRAIL later mapped the basin’s gravitational structure at higher resolution, improving understanding of its subsurface mass distribution.

A standardized astronomical name for a major lunar mare and ancient impact basin; not a commercial brand.

1. 1Mare Humorumen.wikipedia.org