Data from NASA's Moon Mineralogy Mapper (M3) aboard the Indian Chandrayaan-1 probe has shown that there is water locked in mineral grains on the surface on our satellite's surface. Scientists had previously thought that the small amounts of moisture they could detect were all being generated by solar wind and other external factors, but the latest findings are strong evidence that the Moon contains large quantities of its own "magmatic water" from deep within its core.

While the Moon is traditionally thought as a bone-dry place, the evidence for water on its surface has been piling up for decades, although it has been dismissed multiple times.

Four decades ago, the rock samples brought back to Earth by the Apollo astronauts were shown to contain surface water. However, it was assumed that the samples had been contaminated by human handling, and the results were dismissed.

In 2009 NASA's M3 module in the Indian Chandrayaan-1 probe found water near the poles as it mapped the Moon's surface, but this moisture was assumed to be caused by solar winds. Charged particles from the Sun can create thin layers of water molecules on impact, and scientists believed that the small quantity of water that was found could be justified in that way.

Solar winds are known to cause a thin layer of water to accumulate on the surface by the Moon's poles (Image: University of Maryland/F. Merlin/McREL)

Later on in the same year, NASA smashed an impactor into the Cabeus Crater to study the materials that were thrown up in the resulting plume. When they found water vapor and ice particles, they again attributed the findings to the action of solar wind, or possibly to the comet whose impact had formed the Cabeus Crater in the first place.

But the latest results can be hardly equivocated as brought on by human error, solar winds or comets, indicating instead that the Moon contains its own reservoirs of water deep underground (although we don't yet know how they may have gotten there).

NASA's M3 instrument imaged a 37-mile (60-km) wide impact crater called Bullialdus. Unlike previous experiments, this crater is closer to the lunar equator, where scientists believe water from solar winds can't survive on the surface.

Bullialdus's impact crater was so deep that it exposed some of the Moon's magmatic rock. When NASA went about analyzing the crater from orbit, it found something unexpected.

NASA first discovered signs of water in 2009, but they were soon dismissed (Image: NASA)

NASA found that the central portion of the crater contains large amounts of hydroxyl (a molecule made up of one oxygen atom and a hydrogen atom). This is evidence that the rocks in the crater contain water that originated from beneath the surface, which researchers call "magmatic water."

Scientists will now start to compare this water with other characteristics of the lunar surface to learn more about the Moon's internal composition and its volcanic activity evolved as it cooled down to today's temperatures.

The finding also suggests that polar craters could contain more water ice than previously thought. In fact, they could be in large enough quantities that using it as a green propellant to fuel rockets could become a possibility.

A paper on the subject appears in the journal Nature Geoscience.