Lunar ice - AbsoluteAstronomy.com

Lunar water is water that is present on the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. Liquid water cannot persist at the Moon's surface, and water vapour is quickly decomposed by sunlight and lost to outer space. However, scientists have since the 1960s conjectured that water ice

Water ice

Water ice could refer to:# Ice formed by water # Italian ice, fruit flavoured deserts, sorbet# Ice made from flowing water in Ice climbing...

could survive in cold, permanently shadowed craters at the Moon's poles.

Water, and the chemically related hydroxyl

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

group (OH), can also exist in forms chemically bound to lunar minerals (rather than as free water), and evidence strongly suggests that this is indeed the case in low concentrations over much of the Moon's surface. In fact, adsorbed

Adsorption

Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...

water is calculated to exist at trace concentrations of 10 to 1000 parts per million.

Inconclusive evidence of free water ice at the lunar poles was accumulated from a variety of observations suggesting the presence of bound hydrogen. In September 2009, India's Chandrayaan-1 detected water on the Moon and hydroxyl

Hydroxyl

absorption lines in reflected sunlight. In November 2009, NASA reported that its LCROSS

LCROSS

The Lunar Crater Observation and Sensing Satellite 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. The main LCROSS mission objective was to explore the presence of water ice...

space probe had detected a significant amount of hydroxyl group in the material thrown up from a south polar crater by an impactor; this may be attributed to water-bearing materials – what appears to be "near pure crystalline water-ice".
In March 2010 NASA reported Mini-SAR radar aboard the Chandrayaan-1 detected what appear to be ice deposits at the lunar north pole, at least 600 million tonnes in sheets of relatively pure ice at least a couple meters thick.

Water may have been delivered to the Moon over geological timescales by the regular bombardment of water-bearing comet

Comet

A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s, asteroid

Asteroid

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s and meteoroid

Meteoroid

A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...

s or continuously produced in situ by the hydrogen ions (proton

Proton

The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s) of the solar wind

Solar wind

The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

impacting oxygen-bearing minerals.

The search for the presence of lunar water has attracted considerable attention and motivated several recent lunar missions, largely because of water's usefulness in rendering long-term lunar habitation feasible.

20th century

The possibility of ice in the floors of polar lunar craters was first suggested in 1961 by Caltech researchers Kenneth Watson, Bruce C. Murray, and Harrison Brown. Although trace amounts of water were found in lunar rock samples collected by Apollo astronauts, this was assumed to be a result of contamination, and the majority of the lunar surface was generally assumed to be completely dry. However, a 2008 study of lunar rock samples revealed evidence of water molecules trapped in volcanic glass beads.

The first direct evidence of water vapor near the Moon was obtained by the Apollo 14

Apollo 14

Apollo 14 was the eighth manned mission in the American Apollo program, and the third to land on the Moon. It was the last of the "H missions", targeted landings with two-day stays on the Moon with two lunar EVAs, or moonwalks....

ALSEP Suprathermal Ion Detector Experiment, SIDE, on March 7, 1971. A series of bursts of water vapor ions were observed by the instrument mass spectrometer at the lunar surface near the Apollo 14 landing site.

The first proposed evidence of water ice on the Moon came in 1994 from the United States military Clementine probe. In an investigation known as the 'bistatic radar

Bistatic radar

Bistatic radar is the name given to a radar system which comprises a transmitter and receiver which are separated by a distance that is comparable to the expected target distance. Conversely, a radar in which the transmitter and receiver are collocated is called a monostatic radar...

experiment', Clementine used its transmitter to beam radio waves into the dark regions of the south pole of the Moon. Echoes of these waves were detected by the large dish antennas of the Deep Space Network

Deep Space Network

The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...

on Earth. The magnitude and polarisation of these echoes was consistent with an icy rather than rocky surface, but the results were inconclusive, and their significance has been questioned.Resulting computer simulations suggested that an area up to 14,000 km² might be in permanent shadow and hence have the potential to harbour lunar ice.

The Lunar Prospector

Lunar Prospector

The Lunar Prospector mission was the third 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, including mapping of surface composition and possible...

probe, launched in 1998, employed a neutron spectrometer to measure the amount of hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

in the lunar regolith

Regolith

Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

near the polar regions. It was able to determine hydrogen abundance and location to within 50 parts per million and detected enhanced hydrogen concentrations at the lunar north and south poles. These were interpreted as indicating significant amounts of water ice trapped in permanently shadowed craters, but could also be due to the presence of the hydroxyl radical

Hydroxyl radical

The hydroxyl radical, •OH, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides or, in...

(^•OH) chemically bound to minerals. Based on data from Clementine and Lunar Prospector, NASA scientists have estimated that if surface water ice is present, the total quantity could be of the order of 1 to 3 cubic kilometers.

More suspicions about the existence of water on the Moon were generated by inconclusive data produced by Cassini–Huygens mission, which passed the Moon in 1999. In July 1999, at the end of its mission, the Lunar Prospector probe was deliberately crashed into Shoemaker crater

Shoemaker (lunar crater)

Shoemaker is a lunar crater that is located near the southern pole of the Moon, within half a crater diameter of Shackleton. It lies to the south of the crater Malapert, to the east of Haworth, and just to the west of the similar-sized Faustini. The rim of Shoemaker is circular and worn, with some...

, near the Moon's south pole, in the hope that detectable quantities of water would be liberated. However, spectroscopic observations from ground-based telescopes did not reveal the spectral signature of water.

21st century

Deep Impact
In 2005, observations of the Moon by the Deep Impact spacecraft produced inconclusive spectroscopic data suggestive of water on the Moon. In 2006, observations with the Arecibo

Arecibo Observatory

The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...

planetary radar showed that some of the near-polar Clementine radar returns, previously claimed to be indicative of ice, might instead be associated with rocks ejected from young craters. If true, this would indicate that the neutron results from Lunar Prospector were primarily from hydrogen in forms other than ice, such as trapped hydrogen molecules or organics. Nevertheless, the interpretation of the Arecibo data do not exclude the possibility of water ice in permanently shadowed craters. In June 2009, NASA's Deep Impact spacecraft, now redesignated EPOXI

EPOXI

EPOXI is a NASA unmanned space mission led by the University of Maryland using the existing Deep Impact vehicle to begin a new series of observations. It first investigated extrasolar planets and, on November 4, 2010, it performed a close approach to the comet 103P/Hartley...

, made further confirmatory bound hydrogen measurements during another lunar flyby.

Kaguya
As part of its lunar mapping programme, Japan's Kaguya

SELENE

SELENE , better known in Japan by its nickname after the legendary Japanese moon princess, was the second Japanese lunar orbiter spacecraft. Produced by the Institute of Space and Astronautical Science and the National Space Development Agency , both now part of the Japan Aerospace Exploration...

probe, launched in September 2007 for a 19-month mission, carried out gamma ray spectrometry observations from orbit that can measure the abundances of various elements on the Moon's surface. Japan's Kaguya probe's high resolution imaging sensors failed to detect any signs of water ice in permanently shaded craters around the south pole of the Moon, and it ended its mission by crashing into the lunar surface in order to study the ejecta plume content.

Chang'e 1
The People's Republic of China's Chang'e 1 orbiter, launched in October 2007, took the first detailed photographs of some polar areas where ice water is likely to be found.

Chandrayaan-1
On November 14, 2008, the India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

n spacecraft Chandrayaan-1 released the Moon Impact Probe

Moon Impact Probe

The Moon Impact Probe developed by the Indian Space Research Organisation , India's national space agency, was a lunar probe that was released by ISRO's Chandrayaan-1 lunar remote sensing orbiter which in turn was launched, on 22 October 2008, aboard a modified version of ISRO's Polar Satellite...

(MIP) which impacted Shackleton Crater, of the lunar south pole, at 20:31 on 14 November 2008 releasing subsurface debris that was analyzed for presence of water ice.

On September 25, 2009, NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

declared that data sent from its Moon Mineralogy Mapper

Moon Mineralogy Mapper

The Moon Mineralogy Mapper is one of two instruments that NASA contributed to India's first mission to the Moon, Chandrayaan-1, launched October 22, 2008...

(M3) instrument aboard Chandrayaan-1 orbiter confirmed the existence of hydrogen over large areas of the Moon's surface, albeit in low concentrations and in the form of hydroxyl

Hydroxyl

group (OH) chemically bound to soil. This supports earlier evidence from spectrometers aboard the Deep Impact and Cassini probes.
In March 2010, it was reported that the Mini-Sar experiment onboard the Chandrayaan-1 had discovered water ice in small permanently-shadowed lunar craters.

Lunar Reconnaissance Orbiter
The search for lunar ice continued with NASA's Lunar Reconnaissance Orbiter

Lunar Reconnaissance Orbiter

The Lunar Precursor Robotic Program is a program of robotic spacecraft missions which NASA will use to prepare for future human spaceflight missions to the Moon. Two LPRP missions, the Lunar Reconnaissance Orbiter and the Lunar Crater Observation and Sensing Satellite , were launched in June 2009...

(LRO) / LCROSS

LCROSS

mission, launched June 18, 2009. LRO's onboard instruments carried out a variety of observations that may provide further evidence of water. On October 9, 2009, the Centaur

Centaur (rocket stage)

Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. Centaur boosts its satellite payload to geosynchronous orbit or, in the case of an interplanetary space probe, to or near to escape velocity...

upper stage of its Atlas V

Atlas V

Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...

carrier rocket was directed to impact Cabeus crater

Cabeus (crater)

Cabeus is a lunar crater that is located about 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...

at 11:31 UTC, followed shortly by the LCROSS spacecraft that flew into the ejecta plume and attempted to detect the presence of water vapor in the debris cloud. Although no immediate spectacular plume was seen, time was needed to analyze the spectrometry data. On November 13, 2009 NASA reported that after analysis of the data obtained from the ejecta plume, the spectral signature of water had been confirmed. However, what was actually detected was the chemical group hydroxyl (OH), which is suspected to be from water, but could also be hydrate

Hydrate

Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....

s, which are inorganic salts containing chemically-bound water molecules. The nature, concentration and distribution of this material requires further analysis; chief mission scientist Anthony Colaprete has stated that the ejecta appears to include a range of fine-grained particulates of near pure crystalline water-ice. A later definitive analysis found the concentration of water to be "5.6 ± 2.9% by mass". The Mini-RF

Mini-RF

The Miniature Radio-Frequency instrument is a synthetic aperture radar instrument on the Lunar Reconnaissance Orbiter , 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...

instrument on LRO observed the LCROSS landing site and did not detect any evidence of large slabs of water ice, so the water is most likely present as small pieces of ice mixed in with the lunar regolith.
Melt inclusions in Apollo 17 samples
In May 2011, Erik Hauri et al. reported 615-1410 ppm water in melt inclusions

Melt Inclusions

Melt inclusions are small parcels or "blobs" of molten rock that are trapped within crystals that grow in the magmas that form igneous rocks. In many respects they are analogous to fluid inclusions. Melt inclusions are generally small - most are less than 100 micrometres across...

in lunar sample 74220, the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17

Apollo 17

Apollo 17 was the eleventh and final manned mission in the American Apollo space program. Launched at 12:33 a.m. EST on December 7, 1972, with a three-member crew consisting of Commander Eugene Cernan, Command Module Pilot Ronald Evans, and Lunar Module Pilot Harrison Schmitt, Apollo 17 remains the...

mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago.

This concentration is comparable with that of magma in Earth's upper mantle. While of considerable selenological interest, this announcement affords little comfort to would-be lunar colonists. The sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to detect them with a state-of-the-art ion microprobe instrument.

Production

Lunar water has two potential origins: water-bearing comet

Comet

s (and other bodies) striking the Moon, and in situ production. It has been theorized that the latter may occur when hydrogen ions (protons) in the solar wind

Solar wind

chemically combine with the oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

atoms present in the lunar minerals (oxide

Oxide

An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

s, silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s etc.) to produce small amounts of water trapped in the minerals' crystal lattices or as hydroxyl

Hydroxyl

groups, potential water precursors. (This mineral-bound water, or hydroxylated mineral surface, must not be confused with water ice.)

The hydroxyl

Hydroxyl

surface groups (S–OH) formed by the reaction of protons (H⁺) with oxygen

Oxygen

atoms accessible at oxide surface (S=O) could further be converted in water molecules (H₂O) adsorbed onto the oxide mineral's surface. The mass balance of a chemical rearrangement supposed at the oxide surface could be schematically written as follows:

2 S-OH —> S=O + S + H₂O

or,

2 S-OH —> S–O–S + H₂O

where S represents the oxide surface.

The formation of one water molecule requires the presence of two adjacent hydroxyl groups, or a cascade of successive reactions of one oxygen atom with two protons. This could constitute a limiting factor and decreases the probability of water production if the proton density per surface unit is too low.

Trapping

Solar radiation would normally strip any free water or water ice from the lunar surface, splitting it into its constituent elements, hydrogen

Hydrogen

and oxygen

Oxygen

, which then escape to space. However, because of the only very slight axial tilt of the Moon's spin axis to the ecliptic plane

Ecliptic

The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...

(1.5 °), some deep craters near the poles never receive any sunlight, and are permanently shadowed (see, for example, Shackleton crater

Shackleton (crater)

Shackleton is an impact crater that lies at the south pole of the Moon. 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...

). The temperature in these regions never rises above about 100 K

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

(about −170 ° Celsius), and any water that eventually ended up in these craters could remain frozen and stable for extremely long periods of time — perhaps billions of years, depending on the stability of the orientation of the Moon's axis.

Transport

Although free water cannot persist in illuminated regions of the Moon, any such water produced there by the action of the solar wind on lunar minerals might, through a process of evaporation and condensation, migrate to permanently cold polar areas and accumulate there as ice, perhaps in addition to any ice brought by comet impacts.

The hypothetical mechanism of water transport / trapping (if any) remains unknown: indeed lunar surfaces directly exposed to the solar wind where water production occurs are too hot to allow trapping by water condensation (and solar radiation also continuously decomposes water), while no (or much less) water production is expected in the cold areas not directly exposed to the sun. Given the expected short lifetime

Lifetime

Lifetime may refer to:*Life expectancy, the length of time a person is expected to remain alive*Mean lifetime, a certain number that characterizes the rate of reduction of a particle of an assembly...

of water molecules in illuminated regions, a short transport distance would in principle increase the probability of trapping. In other words, water molecules produced close to a cold, dark polar crater should have the highest probability of surviving and being trapped.

To what extent, and at what spatial scale, direct proton exchange (protolysis) and proton surface diffusion

Surface diffusion

Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters at solid material surfaces. The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1...

directly occurring at the naked surface of oxyhydroxide minerals exposed to space vacuum (see surface diffusion

Surface diffusion

and self-ionization of water

Self-ionization of water

The self-ionization of water is the chemical reaction in which a proton is transferred from one water molecule to another, in pure water or an aqueous solution, to create the two ions, hydronium, H3O+ and hydroxide, OH−...

) could also play a role in the mechanism of the water transfer towards the coldest point is presently unknown and remains a conjecture.

Uses

The presence of large quantities of water on the Moon would be an important factor in rendering lunar habitation cost-effective, since transporting water (or hydrogen and oxygen) from Earth would be prohibitively expensive. If future investigations find the quantities to be particularly large, water ice could be mined to provide liquid water for drinking and plant propagation, and the water could also be split into hydrogen and oxygen by solar panel-equipped electric power stations or a nuclear generator, providing breathable oxygen as well as the components of rocket fuel. The hydrogen component of the water ice could also be used to draw out the oxides in the lunar soil and harvest even more oxygen.

Analysis of lunar ice would also provide scientific information about the impact history of the Moon and the abundance of comets and asteroids in the early inner solar system.

Ownership

The hypothetical discovery of usable quantities of water on the Moon may raise legal questions about who owns the water and who has the right to exploit it. The United Nations Outer Space Treaty

Outer Space Treaty

The Outer Space Treaty, formally the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, is a treaty that forms the basis of international space law...

does not prevent the exploitation of lunar resources, but does prevent the appropriation of the Moon by individual nations and is generally interpreted as barring countries from claiming ownership of in-situ resources. The Moon Treaty

Moon Treaty

The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, better known as the Moon Treaty or Moon Agreement, is an international treaty that turns jurisdiction of all celestial bodies over to the international community...

specifically stipulates that exploitation of lunar resources is to be governed by an "international regime", but this treaty has not been ratified by any of the major space-faring nations.

External links

Ice on the Moon — NASA Goddard Space Flight Center
Fluxes of fast and epithermal neutrons from Lunar Prospector: Evidence for water ice at the lunar poles — Science
Moon has a litre of water for every tonne of soil — Times Online
Unambiguous evidence of water on the Moon — Slashdot Science Story

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

20th century

21st century

Production

Trapping

Transport

Uses

Ownership

See also

External links