Solar Particles Could be Source to Water Molecules of Lunar Surface

The water molecules found on the lunar soil is a stream of charged particles from the sun, scientists have concluded.

A team of researchers led by Yang Liu at the University of Tennessee analyzed samples returned to Earth by Apollo missions over the past few years.

In 2009, data collected by NASA's Lunar Crater Observation and Sensing satellite, known as LCROSS, thwarted the long-held assumption that the lunar soil is bone-dry. Observations of the data showed that the lunar crater has material rich in water ice.

Experts also detected that the loose lunar surface soil called as regolith has molecules of water and its precursor hydroxyl. It was believed that water-bearing comets and space debris that strike planets and other bodies are the main source of water in the inner solar system. However, it was unclear how the water molecules appeared in the lunar surface soil.  

The new study found that the water component in the lunar soil is actually from the solar wind, shedding light on another unimagined source that is not known until now, reported Agence France-Presse.

The hydrogen ions (protons) from the sun combines with the oxygen on the surface of the moon to form water and water related compounds like hydroxyl, said the experts. While water contains two hydrogen and one oxygen atom, hydroxyl is water's precursor that has one hydrogen and oxygen atom each.

"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," Zhang, the James R. O'Neil Collegiate Professor of Geological Sciences, said in a statement from University of Michigan.

"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," he said.

The findings suggest that the polar craters on the moon might contain hydrogen atoms originating from the solar wind. But it is still unclear how the hydrogen ions from the solar wind combine with the oxygen in the regolith grains to form water molecules.

Researchers also pointed out that this phenomenon could occur in other planetary bodies where the solar wind comes in direct contact with the surface. This could mean that water likely exists on Mercury that is very close to the sun and asteroid Vesta, which is located in the asteroid belt between Mars and Jupiter, as both have the potential to produce water.

The findings of the study are published in the journal Nature Geoscience.