giovedì 24 settembre 2009

Scoperta l'acqua sulla Luna. Faciliterà le imprese degli astronauti

Nasa's plans to establish a human outpost on the moon have received a surprise boost following the discovery of large amounts of water on its surface. Three spacecraft detected a thin sheen of water locked up in the first few millimetres of lunar soil that could be extracted and used to sustain astronauts on expeditions to our nearest celestial neighbour. Instruments aboard the spacecraft suggest that a cubic metre of soil on the lunar surface could hold around a litre of water. The discovery of water on the moon will bolster Nasa's long-term goal of establishing a permanently crewed outpost there. The space agency is developing a new generation of rockets and crew capsules capable of reaching the moon which are due to fly within five years of the space shuttle fleet being retired next year. "From the long-term space exploration space point of view, it opens an entirely new option to consider as a water resource," said Carle Pieters, a planetary scientist at Brown University in Rhode Island, who led the study. "It has surprised everyone."Since the Apollo missions brought back the first clumps of lunar soil and rock in the 1960s, scientists have worked on the assumption that the moon is bone dry. Small traces of water found in some of the samples were dismissed as contamination picked up while the material was being handled on Earth. The latest discovery came when scientists analysed sunlight glancing off the moon's surface with detectors aboard the Chandrayaan-1 probe, India's first mission to observe the moon. The reflected light was found to be missing infrared wavelengths that are absorbed by water molecules. The results were backed up by further observations from spectrometers aboard Nasa's Deep Impact and Cassini probes. The research will be published in the US journal Science tomorrow. Writing in the journal, Paul Lucey, a planetary scientist at the University of Hawaii, who was not involved in the study, comments: "The most valuable result of these new observations is that they prompt a critical re-examination of the notion that the moon is dry. It is not. "The research paper from the Deep Impact team, led by Jessica Sunshine at the University of Maryland, adds: "Observations of the moon not only unequivocally confirm the presence of [water] on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portions of the lunar day."The water appears to be more abundant at the moon's frigid poles, suggesting that water forms in the soil and gradually moves to cooler regions. Scientists believe the moon formed when a Mars-sized body collided with the Earth some 4.4 billion years ago. In the past 2bn years, asteroids and comets have ploughed into the moon, dumping an estimated ten thousand billion tonnes of water onto its surface. Water is quickly broken down on the lunar surface, but Roger Clark, who led the Cassini study at the US Geological Survey in Colorado, said the new results "could be indicating the presence of that ancient water". Data from the spacecraft found the lunar soils became increasingly damp during sunlight hours, but dried out again at the end of the lunar day. The waves of damp and dry conditions suggest water is created on the moon every day, when hydrogen nuclei in the solar wind slam into oxygen-rich silicate minerals on the moon's surface. If water is created in this way, it could happen on all airless planets throughout the inner Solar System that have oxygen-rich rocks scattered on their surfaces. Next month, Nasa will intentionally crash a probe called LCROSS (Lunar Crater Observation Sensing Satellite Mission) into the Cabeus A crater near the lunar south pole, in the hope of finding signs of water in the shower of debris it produces.

(The Guardian)

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