A permanently shadowed crater is a depression on a body in the Solar System within which lies a point that is always in darkness. [1] [2]
As of 2019, there are 324 known permanently shadowed regions on the Moon. [3] Such regions also exist on Mercury [4] and Ceres. [5]
Such a crater must be located at high latitude (close to a pole) and be on a body with very small axial tilt. The Moon has an axial tilt of about 1.5°; Mercury, 0.03°; [6] and Ceres, about 4°. [7]
On the Moon, permanent shadow can exist at latitudes as low as 58°; approximately 50 permanently shadowed regions exist in the 58°- 65° latitude range for both lunar hemispheres. [8]
The cumulative area of permanently shadowed lunar regions is about 31 thousand km2; more than half of it is in the southern hemisphere. [9]
Craters of eternal darkness might be advantageous for space exploration and colonization, as they preserve sources of water ice [10] that can be converted into drinkable water, breathable oxygen, and rocket propellant. [11] Several of such craters show indications of water ice in their interiors, including Rozhdestvenskiy [12] and Cabeus craters [13] on the Moon, and Juling Crater on Ceres. [14] Other volatiles besides water can also be trapped in such craters, such as mercury. [15] The LCROSS mission additionally found native silver and gold in permanently shadowed craters on the Moon, probably brought there by electrostatic dust transport, and some inconclusive evidence for platinum. Gold was estimated to have a soil mass abundance of 0.52% in these craters from LCROSS data, and mercury 0.39%. This high mercury abundance has been noted as a possible health hazard of water derived from permanently shadowed craters. [16]
The craters may also contain unusually high concentrations of helium-3. [17]
A business case analysis indicates that mining of propellants in the craters could become a profitable commercial enterprise. [18]
In some cases, peaks of eternal light are located nearby, that could be advantageous for solar power generation. For example, there are two peaks near Shackleton Crater that are illuminated a combined ~94% of a lunar year. [19]
Permanently shadowed regions have a stable surface temperature. On the Moon, the temperature hovers somewhere at or below 50 Kelvin. [20] Another temperatures estimate is 25 K to 70 K. [21] The low temperatures make the regions desirable locations for future infrared telescopes. [22] [23]
On the other hand, computer simulations show that powerful solar storms can charge up the soil in permanently shadowed regions near the lunar poles, and may possibly produce "sparks" that could vaporize and melt the soil. [24] [25]
There are other unique challenges of such regions: dark environments that restrict the ability of rovers to perceive their surroundings, cryogenic regolith that could be hard to move on, and communication interruptions. [26]
In 2020, NASA assigned "sensitive location" status to the Moon's permanently shadowed regions to avoid their contamination. [27] The SETI Institute has a contract to manage planetary protection measures for NASA. [28]
Below is an incomplete list of such craters:
The Moon:
Mercury:
In 2009, LCROSS sent an impactor into a Cabeus crater, that resulted in detection of water in the ejected material. [42]
In 2012, The Lyman Alpha Mapping Project aboard NASA's Lunar Reconnaissance Orbiter has found that the permanently shadowed regions have a porous, powdery surface, that indicates the presence of water ice. [43]
In 2018, an analysis of the results of the Moon Mineralogy Mapper confirmed the existence of water ice deposits in permanently shadowed craters and crevices, with more abundance near the south pole. [44]
Lunar Flashlight launched in December 2022 as a secondary payload for the Hakuto-R Mission 1 mission. [45] [46]
A camera called ShadowCam has been built that is able to take high-resolution images of Permanently Shadowed Regions. It is a NASA instrument that flies on board the Korea Pathfinder Lunar Orbiter (KPLO) since 2022. [47]
The proposed International Lunar Observatory mission involves a landing near the Malapert crater. [48]
The Moon is Earth's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Over time Earth's gravity has caused tidal locking, causing the same side of the Moon to always face Earth. Because of this, the lunar day and the lunar month are the same length, at 29.5 Earth days. The Moon's gravitational pull – and to a lesser extent, the Sun's – are the main drivers of Earth's tides.
A lander is a spacecraft that descends towards, then comes to rest on the surface of an astronomical body other than Earth. In contrast to an impact probe, which makes a hard landing that damages or destroys the probe upon reaching the surface, a lander makes a soft landing after which the probe remains functional.
Hermite is a lunar impact crater located along the northern lunar limb, close to the north pole of the Moon. Named for Charles Hermite, the crater was formed roughly 3.91 billion years ago.
The Lunar Precursor Robotic Program (LPRP) is a NASA program that uses robotic spacecraft to prepare for future crewed missions to the Moon. The program gathers data such as lunar radiation, surface imaging, areas of scientific interest, temperature and lighting conditions, and potential resource identification.
Shackleton is an impact crater that lies at the lunar south pole. The peaks along the crater's rim are exposed to almost continual sunlight, while the interior is perpetually in shadow. The low-temperature interior of this crater functions as a cold trap that may capture and freeze volatiles shed during comet impacts on the Moon. Measurements by the Lunar Prospector spacecraft showed higher than normal amounts of hydrogen within the crater, which may indicate the presence of water ice. The crater is named after Antarctic explorer Ernest Shackleton.
Peary is the closest large lunar impact crater to the lunar north pole. At this latitude the crater interior receives little sunlight, and portions of the southernmost region of the crater floor remain permanently cloaked in shadow. From the Earth the crater appears on the northern lunar limb, and is seen from the side.
Cabeus is a lunar impact crater that is located about 100 km (62 mi) from the south pole of the Moon. At this location the crater is seen obliquely from Earth, and it is almost perpetually in deep shadow due to lack of sunlight. Hence, not much detail can be seen of this crater, even from orbit. Through a telescope, this crater appears near the southern limb of the Moon, to the west of the crater Malapert and to the south-southwest of Newton.
A peak of eternal light (PEL) is a hypothetical point on the surface of an astronomical body that is always in sunlight. Such a peak must have high latitude, high elevation, and be on a body with very small axial tilt. The existence of such peaks was first postulated by Beer and Mädler in 1837. The pair said about the lunar polar mountains: "...many of these peaks have eternal sunshine". These polar peaks were later mentioned by Camille Flammarion in 1879, who speculated that there may exist pics de lumière éternelle at the poles of the Moon. PELs would be advantageous for space exploration and colonization due to the ability of an electrical device located there to receive solar power regardless of the time of day or day of the year, and the relatively stable temperature range.
Lunar water is water that is present on the Moon. Diffuse water molecules in low concentrations can persist at the Moon's sunlit surface, as discovered by the SOFIA observatory in 2020. Gradually, water vapor is decomposed by sunlight, leaving hydrogen and oxygen lost to outer space. Scientists have found water ice in the cold, permanently shadowed craters at the Moon's poles. Water molecules are also present in the extremely thin lunar atmosphere.
The geology of Mercury is the scientific study of the surface, crust, and interior of the planet Mercury. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geology. In planetary science, the term geology is used in its broadest sense to mean the study of the solid parts of planets and moons. The term incorporates aspects of geophysics, geochemistry, mineralogy, geodesy, and cartography.
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 immediately after discovery of lunar water by Chandrayaan-1, the main LCROSS mission objective was to further explore the presence of water in the form of ice in a permanently shadowed crater near a lunar polar region. It was successful in confirming water in the southern lunar crater Cabeus.
Ceres is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid, discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily, and announced as a new planet. Ceres was later classified as an asteroid and then a dwarf planet, the only one always inside Neptune's orbit.
A cold trap is a concept in planetary sciences that describes an area cold enough to freeze (trap) volatiles. Cold-traps can exist on the surfaces of airless bodies or in the upper layers of an adiabatic atmosphere. On airless bodies, the ices trapped inside cold-traps can potentially remain there for geologic time periods, allowing us a glimpse into the primordial solar system. In adiabatic atmospheres, cold-traps prevent volatiles from escaping the atmosphere into space.
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 to the Moon. Its detailed mapping program is identifying safe landing sites, locating potential resources on the Moon, characterizing the radiation environment, and demonstrating new technologies.
The lunar south pole is the southernmost point on the Moon. It is of 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 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.
The Miniature Radio-Frequency instrument (Mini-RF) is a synthetic aperture radar (SAR) instrument on the Lunar Reconnaissance Orbiter (LRO), which is currently in orbit around the Moon. It has a resolution of 30 m/pixel and two wavelength bands, a primary band at 12.6 cm and a secondary band at 4.2 cm. The original principal investigator of Mini-RF, Stewart Nozette, was arrested for espionage. Nozette was replaced by Ben Bussey, then of APL, the Applied Physics Laboratory where Mini-RF was assembled from components developed by a consortium of industry team members. Bussey accepted a position at NASA Headquarters and was replaced by the current principal investigator, Wes Patterson, also of APL. Previous SAR instruments, such as the radar on the Magellan mission to Venus, were large, massive, power-hungry, and expensive. Intended as a demonstration of cheap, lightweight SAR technology, the Mini-RF instrument was designed in response to these concerns. Because it was a technology demonstration, Mini-RF is sometimes not included in lists of LRO's instruments.
The following outline is provided as an overview of and topical guide to the Moon:
The Moon bears substantial natural resources which could be exploited in the future. Potential lunar resources may encompass processable materials such as volatiles and minerals, along with geologic structures such as lava tubes that, together, might enable lunar habitation. The use of resources on the Moon may provide a means of reducing the cost and risk of lunar exploration and beyond.
VIPER is a lunar rover developed by NASA, and currently planned to be delivered to the surface of the Moon in November 2024. The rover will be tasked with prospecting for lunar resources in permanently shadowed areas in the lunar south pole region, especially by mapping the distribution and concentration of water ice. The mission builds on a previous NASA rover concept called Resource Prospector, which was cancelled in 2018.
Lunar Trailblazer is a planned small lunar orbiter, part of NASA's SIMPLEx program, that will detect and map water on the lunar surface to determine how its form, abundance, and location relate to geology. Its mission is to aid in the understanding of lunar water and the Moon's water cycle. Lunar Trailblazer is currently slated to launch in 2024 as a secondary payload on the IM-2 mission. The Principal Investigator (PI) of the mission is Bethany Ehlmann, a professor at Caltech.
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