New research says that charged particles from the sun or solar winds, bombarding the lunar surface, could explain the presence of water locked inside its soil.
Over the past five years, spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the moon is bone-dry.
In 2009, NASA's Lunar Crater Observation and Sensing satellite, known as LCROSS, slammed into a permanently shadowed lunar crater and ejected a plume of material that was surprisingly rich in water ice, the journal Nature Geoscience reports.
Water and related compounds have also been detected in the lunar regolith, or the layer of fine powder and rock fragments that coats the lunar surface. But the origin of lunar surface water has remained unclear, according to a Michigan University statement.
The findings from University of Michigan researcher Youxue Zhang and colleagues from the University of Tennessee (U-T) and the California Institute of Technology support solar-wind production of water ice on the moon.
"We found that the 'water' component, the hydroxyl, in the lunar regolith is mostly from solar wind implantation of protons, which locally combined with oxygen to form hydroxyls that moved into the interior of glasses by impact melting," said Zhang, professor of geological sciences.
"Lunar regolith is everywhere on the lunar surface, and glasses make up about half of lunar regolith. So our work shows that the 'water' component, the hydroxyl, is widespread in lunar materials, although not in the form of ice or liquid water that can easily be used in a future manned lunar base."
The findings imply that ice inside permanently shadowed polar craters on the moon, sometimes called cold traps, could contain hydrogen atoms ultimately derived from the solar wind, the researchers report.
The researchers analysed individual grains from Apollo 11 mare soil, Apollo 16 highland soil and Apollo 17 mare soil.