Lunar ice
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Lunar ice is water ice that is hypothesised to exist on the surface of the Moon, delivered over geological timescales by the regular bombardment of the Moon by comets, asteroids and meteoroids. Energy from sunlight usually splits this water into its constituent elements hydrogen and oxygen, which generally escape to space. Attesting to the dryness of lunar rocks, the samples collected by Apollo astronauts near the equator have been found to contain no trace of water.[1]
However, because of the only very slight axial tilt of the Moon's spin axis to the ecliptic plane (only 1.5°), some deep craters near the poles never receive any light from the Sun, and are permanently shadowed (see, for example, Shackleton crater). The temperature in these regions never rises above about 100 K (about −170 degrees Celsius),[2] and any water that eventually ended up in these craters could remain frozen and stable for extremely long periods of time — probably billions of years.[3] The quantities (if any) and concentrations of this water ice are at present unknown, but it has been suggested that, at the south pole at least, any lunar ice is more likely to exist as small grains widely dispersed in the regolith rather than as thick deposits.[4]
The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation cost-effective, since transporting water (or hydrogen and oxygen) from Earth would be prohibitively expensive. 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.
Analysis of lunar ice, should it be found, will also provide scientific information about the impact history of the Moon and the abundance of comets and asteroids in the early inner solar system.
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[edit] Evidence for lunar ice
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.[5]
In 1994, the Clementine probe mapped craters at the lunar south pole,[6] and computer simulations suggest that an area up to 14,000 km² might be in permanent shadow and hence have the potential to harbour lunar ice.[7] Further, use was made of the probe's radio transmitting functionality to form a bistatic radar. Results from the Clementine mission bistatic radar experiment are consistent with small, frozen pockets of water close to the surface, and data from the Lunar Prospector neutron spectrometer indicate that anomalously high concentrations of hydrogen are present in the upper meter of the regolith near the polar regions.[8] Based on data from Clementine and Lunar Prospector, NASA has estimated that the total quantity of water ice may be close to one cubic kilometer.[9]
In July 1999, at the end of its mission, Lunar Prospector was deliberately crashed into Shoemaker crater, near the Moon's south pole, in the hope that detectable quantities of water would be liberated. Spectroscopic observations from ground-based telescopes did not reveal the signature of water, however.[10]
More recently, in 2006, observations with the Arecibo planetary radar showed that some of the near-polar Clementine radar returns might instead be associated with rocks ejected from young craters. If true, this would indicate that the neutron results are primarily from hydrogen in forms other than ice, such as trapped hydrogen molecules or organics. Nevertheless, the interpretation of these data is non-unique (ice or surface roughness could give rise to the observed signature), and it appears that these results do not exclude the possibility of water ice in permanently shadowed craters.[11]
The search for lunar ice will continue with NASA's Lunar Reconnaissance Orbiter (LRO) mission, scheduled for launch in October 2008. LRO's onboard instruments will carry out a variety of observations that may provide further evidence of water. The LCROSS component of the mission will impact the spent upper stage of the launch vehicle into a polar lunar crater, closely followed by a small probe that will fly into the ejecta plume and attempt to detect the presence of water.[12]
As part of its lunar mapping programme, JAXA's Kaguya probe, launched in September 2007 for a nominal one year mission, is carrying out gamma ray spectrometry observations from orbit that can measure the abundances of various elements on the Moon's surface. Detection of hydrogen may indicate the presence of water.[13] China's Chang'e 1 orbiter, launched in October 2007, will take the first detailed photographs of some polar areas where water is likely to be found.[14] Instruments on board India's Chandrayaan-1 orbiter will be able to detect water ice up to a depth of several metres,[15] and the Russian Luna-Glob programme includes plans to deploy penetrators and a lander to search directly for water ice.[14]
[edit] Ownership
The 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, which has been ratified by most space-faring nations, 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.[16][17] The Moon Treaty 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.[18]
[edit] See also
[edit] References
- ^ lunar2
- ^ Ice on the Moon, NASA
- ^ lunar2
- ^ Hopes for lunar ice melt away, New Scientist, October 2006
- ^ lunar2
- ^ Lunar Polar Composites (GIF). Retrieved on 2006-03-20.
- ^ Linda, Martel (June 4, 2003). The Moon's Dark, Icy Poles.
- ^ Eureka! Ice found at lunar poles (August 31, 2001).
- ^ Prospecting for Lunar Water, NASA
- ^ No water ice detected from Lunar Prospector, NASA website
- ^ Paul Spudis (2006). Ice on the Moon.
- ^ LCROSS mission overview, NASA
- ^ Kaguya Gamma Ray Spectrometer, JAXA
- ^ a b "Who's Orbiting the Moon?", NASA, February 20, 2008
- ^ Chandrayaan-1, BNSC
- ^ Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies ("Outer Space Treaty"), UN Office for Outer Space Affairs
- ^ "Moon Water: A Trickle of Data and a Flood of Questions", space.com, March 6, 2006
- ^ Agreement Governing the Activities of States on the Moon and Other Celestial Bodies ("Moon Treaty"), UN Office for Outer Space Affairs
[edit] 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
- Clementine Bistatic Radar Experiment
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