The lunar south pole is the southernmost point on the Moon, at 90°S. It is of special interest to scientists because of the occurrence of water ice in permanently shadowed areas around it. The lunar south pole region features craters that are unique in that the near-constant sunlight does not reach their interior. Such craters are cold traps that contain a fossil record of hydrogen, water ice, and other volatiles dating from the early Solar System. In contrast, the lunar north pole region exhibits a much lower quantity of similarly sheltered craters.

Geography

The lunar south pole is located on the center of the polar Antarctic Circle (80°S to 90°S).Lunar South Pole.
NASA. 2017. Accessed on 16 July 2019. The lunar south pole has shifted 5 degrees from its original position billions of years ago. This shift has changed the rotational axis of the Moon, allowing sunlight to reach previously shadowed areas, but the south pole still features some completely shadowed areas. The axis spin is 88.5 degrees from the plane of the elliptic. On the contrary, the pole also contains areas with permanent exposure to sunlight. The south pole region features many craters and basins such as the South Pole–Aitken basin, which appears to be one of the most fundamental features of the Moon, and mountains, such as Epsilon Peak at 9.050 km, taller than any mountain found on Earth.Lunar South Pole
(2017). Fossweb.com. Retrieved 29 March 2017. The south pole temperature averages at approximately .

Craters

The rotational axis 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 ...

lies within Shackleton Crater. Notable craters nearest to the lunar south pole include De Gerlache,

Sverdrup In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): 1 Sv is equal to 1 hm3/s. It is u ...

Shoemaker Shoemaking is the process of making footwear. Originally, shoes were made one at a time by hand, often by groups of shoemakers, or cobblers (also known as ''cordwainers''). In the 18th century, dozens or even hundreds of masters, journeymen an ...

, Faustini,

Haworth Haworth () is a village in the City of Bradford, West Yorkshire, England, in the Pennines, south-west of Keighley, west of Bradford and east of Colne in Lancashire. The surrounding areas include Oakworth and Oxenhope. Nearby villages inc ...

, Nobile, and Cabeus.

Discoveries

Illumination

The lunar south pole features a region with crater rims exposed to near constant solar illumination, yet the interior of the craters are permanently shaded from sunlight. The area's illumination was studied using high resolution digital models produced from data by the

Lunar Reconnaissance Orbiter The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon in an eccentric polar mapping orbit. Data collected by LRO have been described as essential for planning NASA's future human and robotic missions t ...

. The lunar surface can also reflect

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

as energetic neutral atoms. On average, 16% of these atoms have been protons that varies based on location. These atoms have created an integral flux of

backscatter In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, a ...

ed hydrogen atoms due to the reflected amount of plasma that exists on the surface of the Moon. They also reveal the line boundary and the magnetic dynamics within the regions of these neutral atoms on the Moon' surface.

Cold traps

Cold traps are some of the important places on the lunar south pole region in terms of possible water ice and other volatile deposits. Cold traps can contain water and ice that were originally from

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

s and

-induced iron reduction. From experiments and sample readings, scientists were able to confirm that cold traps do contain ice.

Hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

has also been found in these cold traps. The discovery of these two compounds has led to the funding of missions focusing primarily on the lunar poles using global scale infrared detection. The ice stays in these traps because of the thermal behavior of the Moon that are controlled by thermophysical properties such as scattered sunlight, thermal re-radiation, internal heat and light given off by the Earth.

Magnetic surface

There are areas of the Moon where the crust is magnetized. This is known as a magnetic anomaly due to the remnants of metal iron that was emplaced by the impactor that formed the South Pole–Aitken basin (SPA basin). However, the concentration of iron that is thought to be in the basin was not present in the mappings, as they could be too deep in the Moon's crust for the mappings to detect. Or the magnetic anomaly is caused by another factor that does not involve metallic properties. The findings were proven inadequate due to the inconsistencies between the maps that were used, and also, they were not able to detect the magnitude of the magnetic fluctuations at the Moon's surface.

Exploration

Missions

Orbiters from several countries have explored the region around the lunar south pole. Extensive studies were conducted by the Lunar Orbiters, Clementine,

Lunar Prospector ''Lunar Prospector'' was the third mission selected by NASA for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19-month mission was designed for a low polar orbit investigation of the Moon ...

, Kaguya, and

Chandrayaan-1 Chandrayaan-1 (, ) was the first Indian lunar probe under the Chandrayaan program. It was launched by the Indian Space Research Organisation in October 2008, and operated until August 2009. The mission included a lunar orbiter and an impact ...

, that discovered the presence of

lunar water Lunar water is water that is present on the Moon. Diffuse water molecules can persist at the Moon's sunlit surface, as discovered by NASA's SOFIA observatory in 2020. Gradually water vapor is decomposed by sunlight, leaving hydrogen and oxyg ...

. NASA's

LCROSS The Lunar Crater Observation and Sensing Satellite (LCROSS) was a robotic spacecraft operated by NASA. The mission was conceived as a low-cost means of determining the nature of hydrogen detected at the polar regions of the Moon. Launched immed ...

mission found a significant amount of water in Cabeus. NASA's

mission deliberately crashed into the floor of Cabeus and from samples found that it contained nearly 5% water. The Lunar Reconnaissance Orbiter (LRO) was launched on 18 June 2009 and is still mapping the lunar south pole region. This mission will help scientists see if the lunar south pole region has enough sustainable resources to sustain a permanent crewed station. The LRO carries the Diviner Lunar Radiometer Experiment, which is investigating the radiation and thermophysical properties of the south pole surface. It can detect reflected solar radiation and internal infrared emissions. The LRO Diviner is able to detect where water ice could be trapped on the surface. On 3 January 2019, the

Chang'e 4 Chang'e 4 (; ) is a robotic spacecraft mission, part of the second phase of the Chinese Lunar Exploration Program. China achieved humanity's first soft landing on the far side of the Moon, on 3 January 2019. A communication relay satellit ...

, a Chinese spacecraft, was the first to soft land (45.5 ° S, 177.6 ° E) in the Von Kármán crater,China's Journey to the Lunar Far Side: A Missed Opportunity?
Paul D. Spudis, ''Air & Space Smithsonian''. 14 June 2017. which is within the immense South Pole-Aitken Basin on the southern

far side of the Moon The far side of the Moon is the lunar hemisphere that always faces away from Earth, opposite to the near side, because of synchronous rotation in the Moon's orbit. Compared to the near side, the far side's terrain is rugged, with a multitu ...

. India's second lunar mission Chandrayaan-2, which was launched on 22 July 2019, attempted to soft-land on the south polar region of the Moon between 70.90267°S 22.78110°E and 67.87406°S 18.46947°W. The lander failed to land safely, losing communication barely 335m from the ground.Vikram lander located on lunar surface, wasn't a soft landing: Isro.
''Times of India''. 8 September 2019.

Role in the future exploration and observations

The lunar south pole region is deemed as a compelling spot for future exploration missions and suitable for a lunar outpost. The permanently shadowed places on the Moon could contain ice and other minerals, which would be vital resources for future explorers. The mountain peaks near the pole are illuminated for large periods of time and could be used to provide solar energy to an outpost. With an outpost on the Moon scientists will be able to analyze water and other volatile samples dating back to the

formation of the Solar System The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a ...

. Scientists used LOLA (Lunar Orbiter Laser Altimeter), which was a device used by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

to provide an accurate topographic model of the Moon. With this data locations near the south pole at Connecting Ridge, which connects Shackleton Crater to the de Gerlache crater, were found that yielded sunlight for 92.27–95.65% of the time based on altitude ranging from 2 m above ground to 10 m above ground. At the same spots it was discovered that the longest continuous periods of darkness were only 3 to 5 days. The lunar south pole is a place where scientists may be able to perform unique astronomical observations of radio waves under 30 MHz. The Chinese ''Longjiang'' microsatellites were launched in May 2018 to orbit the Moon, and ''Longjiang-2'' operated in this frequency until 31 July 2019.Chang'e-4 lunar far side mission to carry microsatellites for pioneering astronomy
. Andrew Jones, ''GB Times''. March 2018.The scientific objectives and payloads of Chang'E−4 mission
(PDF) Yingzhuo Jia, Yongliao Zou, Jinsong Ping, Changbin Xue, Jun Yan, Yuanming Ning. ''Planetary and Space Science''. 21 February 2018. Before ''Longjiang-2'', no space observatory had been able to observe astronomical radio waves in this frequency because interference waves from equipment on Earth. Though facing Earth the lunar south pole has mountains and basins, like the south side of Malapert Mountain that are not facing Earth and would be an ideal place to receive such astronomical radio signals from a ground radio observatory.

Resources

Solar power, oxygen, and metals are abundant resources on the south polar region. By locating a lunar resource processing facility near the south pole, solar-generated electrical power will allow for nearly constant operation. Elements known to be present on the lunar surface include, among others,

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

(H),

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

(O),

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

(Si),

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

(Fe),

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

(Mg),

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

(Ca),

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

(Al),

manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...

(Mn) and

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...

(Ti). Among the more abundant are oxygen, iron and silicon. The oxygen content is estimated at 45% (by weight).

Future

Blue Origin Blue Origin, LLC is an American private spaceflight, privately funded aerospace manufacturer and sub-orbital spaceflight services company headquartered in Kent, Washington. Founded in 2000 by Jeff Bezos, the founder and executive chairman of Am ...

is planning a mission to the south polar region in about 2024.'Moon Race' Backed by Blue Origin, Airbus Aims for 2024 Lunar Flight
Elizabeth Howell, ''Space.com''. October 3, 2018. The ''Blue Moon'' lander derives from the vertical landing technology used in Blue Origin's

New Shepard New Shepard is a fully reusable suborbital launch vehicle developed by Blue Origin for space tourism. The vehicle is named after Alan Shepard, the first American astronaut in space. The vehicle is capable of vertical takeoff and vertical lan ...

sub-orbital rocket. This would lead to a series of missions landing equipment for a crewed base in a south polar region crater using their Blue Moon lander. NASA's

Artemis program The Artemis program is a robotic and human Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA) along with three partner agencies: European Space Agency (ESA), Japan Aerospace Exploration ...

has proposed to land several robotic landers and rovers ( CLPS) in preparation for the 2025 Artemis 3 crewed landing at the south polar region. Following Chandrayaan-2, where a last-minute glitch in the soft landing guidance software led to the failure of the lander's soft landing attempt after a successful orbital insertion, another lunar mission for demonstrating soft landing was proposed. Chandrayaan-3 will be a mission repeat of Chandrayaan-2 but will only include a lander and rover similar to that of Chandrayaan-2. It will not have an orbiter. The spacecraft is planned to be launched in the third quarter of 2022.

References

External links

USGS Astrogeology Science Center: Moon
* {{The Moon

South Pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...