Moon's water could be generated by the Earth's magnetosphere

Before humans stepped on the moon's surface, it was thought to be dry as a desert. Since the Apollo era, scientists have discovered that water does exist on the moon in the form of ice in craters that exist in eternal shadow. Water is also found in volcanic rocks, and there are unexpected rusty iron soil deposits in the lunar soil. There still has been no true confirmation of the extent or origin of lunar surface water.

The prevailing theory is that positively charged hydrogen ions propelled by the solar wind impact the lunar surface and react to make water. However, a new study published recently proposes a different theory. According to the study, solar wind may not be the only source of water-forming ions. Researchers have shown that particles from the Earth can seed the moon with water.

The solar wind is a likely source of lunar surface water. Computer models have predicted that up to half of it should evaporate and disappear at higher latitude regions over roughly the days of the full moon when it passes into the Earth's magnetosphere. The latest analysis of lunar surface hydroxyl/water came from the Chandrayaan-1 Moon Mineralogy Mapper that shows lunar surface water does not disappear when the Earth's magnetosphere shields the moon.

Earth's magnetic field was previously believed to block the solar wind from reaching the moon, so water could not be regenerated faster than it was lost, but it's been discovered that is not the case. Researchers have compared a time series of water surface maps from before, during, and after the lunar magnetosphere transit. Researchers say lunar water could be replenished by flows of magnetosphere ions, known as the "Earth wind."

Satellite observations confirmed the presence of those ions from Earth near the moon. Observations from the Kaguya satellite during the full moon detected high concentrations of oxygen isotopes that leaked from the Earth's ozone layer and embedded in lunar soil along with hydrogen ions.