Where did Moon get its water from? Scientists discover big lunar secret

The solar wind — a continuous flow of high-speed protons (hydrogen nuclei) emitted by the Sun—bombards the Moon’s airless surface at over a million miles per hour. Unlike Earth, which is shielded by a magnetic field and atmosphere, the Moon’s surface is directly exposed.

When these protons collide with the lunar soil, or regolith, they capture electrons and form hydrogen atoms. These hydrogen atoms then bond with oxygen atoms abundant in lunar minerals, creating hydroxyl (OH) and water (H2O) molecules just millimeters deep in the soil.

To confirm this process, Nasa scientists Li Hsia Yeo and Jason McLain designed a unique experimental chamber that simulated the Moon’s vacuum environment while bombarding Apollo 17 lunar soil samples with a beam mimicking solar wind. By baking the samples beforehand to remove any Earth-based moisture, the team ensured uncontaminated results.

After exposing the dust to simulated solar wind equivalent to 80,000 years of lunar exposure within days, they detected a distinct infrared signature near 3 microns—a telltale sign of water and hydroxyl molecules forming in the samples.

This discovery has big implications for Nasa’s Artemis program, which plans to establish a sustainable human presence at the Moon’s South Pole, where much of the water is believed to be frozen in permanently shadowed craters.

The finding suggests that water on the Moon is not just a relic but may be continuously replenished by solar wind interactions, creating a dynamic lunar water cycle.

“The exciting thing here is that with only lunar soil and a basic ingredient from the Sun, which is always spitting out hydrogen, there’s a possibility of creating water,” said Yeo.

This insight could revolutionise future lunar exploration by enabling astronauts to harvest water directly from the lunar surface, supporting life and fuel production beyond Earth.