How the Sun might be making water on the Moon

Water on the Moon has long fascinated scientists, not just because it’s crucial for future lunar missions, but also because it raises a big question: where did it come from? Since the 1960s, researchers have proposed that water might be forming thanks to the sun.

The idea is simple yet powerful: when charged particles from the Sun hit the Moon’s surface, they might spark a chemical reaction that produces water. That theory now has strong experimental support.

Is the Sun creating the Moon’s water?

Researchers at NASA’s Goddard Space Flight Center and their collaborators have confirmed this process in the lab. They used one of the most realistic simulations of solar wind hitting lunar dust to date.

The findings could have a big impact on how NASA plans future missions, especially to the Moon’s South Pole – where frozen water may lie in shadowed craters, a potential goldmine for exploration.

“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. That’s incredible to think about,” said Li Hsia Yeo, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland who led the study.

Solar wind and water formation

The Sun constantly blasts the solar system with a stream of particles called the solar wind. These particles travel at over one million miles per hour and are mostly made of hydrogen protons.

Earth has a magnetic field and an atmosphere that protect it from this bombardment, but the Moon doesn’t. With no protection, its dusty surface – made of a gritty, rocky material called regolith – is fully exposed.

When solar wind protons hit this regolith, they can pick up electrons, becoming hydrogen atoms. These atoms then move through the lunar surface and bond with oxygen in minerals like silica.

The result? Molecules of hydroxyl (OH) and, sometimes, actual water (H₂O). Evidence of both hydroxyl and water has been found in the Moon’s uppermost surface – just a few millimeters deep.

Scientists detect these molecules through their chemical “fingerprint” using light analysis. But distinguishing between hydroxyl and water is tricky, so researchers often use “water” as a catch-all term.

The Moon’s dynamic water signature

Previous spacecraft observations hinted that solar wind might be actively generating this water. One major clue is that the Moon’s water signature changes over the course of a day.

In some places, the signal is stronger in the cooler morning and weakens in the heat of the afternoon. Then it returns at night. This suggests the water isn’t static – it’s dynamic, possibly being made and lost on a daily basis.

Bringing the Moon to the lab

To test the solar wind theory, Yeo and her colleague, Jason McLain, built a unique lab setup. It was the first of its kind to keep lunar samples sealed in a vacuum during testing – eliminating the risk of contamination from Earth’s moisture.

“It took a long time and many iterations to design the apparatus components and get them all to fit inside,” said McLain. “But it was worth it, because once we eliminated all possible sources of contamination, we learned that this decades-old idea about the solar wind turns out to be true.”

The team used lunar dust from Apollo 17 – collected back in 1972 – and baked it to remove any trace water it might have picked up since. Then they bombarded the samples with high doses of mock solar wind using a tiny particle accelerator. This simulated about 80,000 years of lunar exposure.

Detecting a molecular signal

To track changes, the researchers used a spectrometer – a tool that measures how light reflects off materials. They spotted a very specific dip in the light signal, right near the infrared wavelength where water usually absorbs energy.

This dip is the telltale sign that something like water had formed. Although they can’t say for sure whether it was hydroxyl or full water molecules, the signal strongly suggests both were produced.

The results support the idea that the Sun plays a major role in forming water on the Moon through solar wind.

Water creation by the Sun

Understanding where and how water forms on the moon isn’t just a scientific curiosity. It could shape how future astronauts explore the lunar surface.

If solar wind really is making water, even in tiny amounts, then lunar soil itself could become a resource – potentially useful for drinking water, breathable oxygen, or even rocket fuel.

And now, thanks to one carefully sealed chamber and a bit of lunar dust from the past, that possibility looks a lot more real.

The full study was published in the journal Journal of Geophysical Research: Planets.

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