Mare Smythii (

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "Smyth's Sea") is a

lunar mare The lunar maria (; singular: mare ) are large, dark, basaltic plains on Earth's Moon, formed by ancient asteroid impacts on the far side on the Moon that triggered volcanic activity on the opposite (near) side. They were dubbed , Latin for 'seas' ...

located along the equator on the easternmost edge of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

's near side. It is named for the 19th-century British astronomer

William Henry Smyth Admiral William Henry Smyth (21 January 1788 – 8 September 1865) was a Royal Navy officer, hydrographer, astronomer and numismatist. He is noted for his involvement in the early history of a number of learned societies, for his hydrographic ...

. The Smythii basin where the mare is located is of the

Pre-Nectarian The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Necta ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

, while the surrounding features are of the Nectarian system. It is contained within a minimal diameter of , and has been excavated to a depth of . The mare material, which makes up the floor of the mare, is a low alumina

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

, and consists of

Upper Imbrian The Imbrian is a lunar geologic period divided into two epochs, the Early and Late. Early Imbrian In the lunar geologic timescale, the Early Imbrian epoch occurred from 3,850 million years ago to about 3,800 million years ago. It overlaps the en ...

basalt covered by

Eratosthenian The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface ...

basalt. Features observed within the basin include wrinkle ridges, submerged "ghost" craters,

domes A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

crater chain A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena , plural catenae (Latin for "chain"), as specified by the International Astronomical Union's rules on planetary nome ...

s, and

rille Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon that resemble channels. The Latin term is ''rima'', plural ''rimae''. Typically, a rille can be several kilometers wid ...

s. The overall shape of the mare is circular, likely the result of a large impact. Further bombardment followed, creating the irregular shape. Subsequent volcanism laid down the mare material. As a result of this sequence, only the northeastern portion and a smaller area in the western central contain significant regions of smooth mare material. The remaining surface is more hummocky with a higher albedo. The geological features suggest that lava flowed from the southeast and west toward the northeast, where it accumulated in the lowest parts of the basin. Mare Smythii contains a relatively high number of craters with fractured floors, including the noticeably unusual crater Haldane. This is probably a result of uplift from injection of magma below the mare. The crater Neper is located to the north of the mare. This crater makes up part of the southern rim of

Mare Marginis Mare Marginis (Latin ''marginis'', the "Sea of the Edge") is a lunar mare that lies on the very edge of the lunar nearside. The selenographic coordinates of this feature are 13.3° N, 86.1° E, and the diameter is 358 km. The name is Latin ...

. Just off to the northwest of the mare are the craters

Schubert Franz Peter Schubert (; 31 January 179719 November 1828) was an Austrian composer of the late Classical and early Romantic eras. Despite his short lifetime, Schubert left behind a vast ''oeuvre'', including more than 600 secular vocal wor ...

and Schubert B. The dark mare-filled crater at the southern edge of Smythii is the crater Kästner.

Gallery

File:MareSmithiiTG.jpg, The topography (top) and corresponding gravity (bottom) signal of Mare Smythii reveals a

mascon In astronomy, astrophysics and geophysics, a mass concentration (or mascon) is a region of a planet's or moon's crust that contains a large positive gravity anomaly. In general, the word "mascon" can be used as a noun to refer to an excess dist ...

in its center File:Smythii basin topo.jpg, Topographic map File:Smythii basin GRAIL gravity.jpg, Gravity map based on

GRAIL The Gravity Recovery and Interior Laboratory (GRAIL) was an American lunar science mission in NASA's Discovery Program which used high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraf ...

File:Mare Smythii AS10-27-3915.jpg, View from

Apollo 10 Apollo 10 (May 18–26, 1969) was a human spaceflight, the fourth crewed mission in the United States Apollo program, and the second (after Apollo8) to orbit the Moon. NASA described it as a "dress rehearsal" for the first Moon landing, and ...

File:Mare Smythii AS16-M-3008.jpg, Oblique view from

Apollo 16 Apollo 16 (April 1627, 1972) was the tenth crewed mission in the United States Apollo space program, administered by NASA, and the fifth and penultimate to land on the Moon. It was the second of Apollo's " J missions", with an extended sta ...

References

{{Lunar maria Smythii Smythii Smythii Smythii