A Solar Surprise: Water on the Moon Comes from the Sun
Scientists have been attempting to unlock the secret of water on the Moon for decades. How could a dry, airless Moon harbor any water whatsoever? Now, NASA researchers may have discovered the solution, and it’s coming from a very surprising source: the Sun. In a never-before-seen lab experiment, researchers managed to simulate the conditions of space and subject actual Moon dirt to a flow of artificial solar wind—charged particles akin to those that the Sun emits continuously. The findings, released on March 17 in *JGR Planets*, are strong indications that solar wind plays an essential role in producing water on the surface of the Moon.
Simulating Space in the Lab
To experimentally validate this hypothesis, NASA scientists have devised a specialized test apparatus imitating the rough space environment. With samples of lunar soil, gathered by astronauts on board the Apollo 17 mission, the scientists made certain that they maintained the Earth environment away from all contaminants. Then, they packed the samples inside a vacuum vessel to replicate the Moon’s lack of atmosphere. Finally, a beam of similar solar wind ionized particles showered over the soil. And why? To determine whether this bombardment might initiate the chemical processes required to create water or hydroxyl (OH) molecules.
How Solar Wind Ignites Water Creation
When the Sun emits solar wind, it shoots out a stream of constant, high-energy protons—basically hydrogen ions. On our planet, our magnetic field and atmosphere shield us from this radiation. But the Moon has no such shield, so it takes the brunt. These solar wind protons infiltrate the lunar surface, where they start to interact with the minerals of the regolith (Moon dust). The protons rob electrons from the surface materials, becoming neutral hydrogen atoms. These atoms can then bond with oxygen atoms already in the Moon’s minerals, forming either hydroxyl (OH) or water (H₂O) molecules just below the surface.
Altering Signals Across the Moon’s Day
Spacecraft circling the Moon have detected for years the presence of water on the Moon’s surface. But more recent observations showed an unusual trend: signals of water changed over the course of a lunar day. Early morning, when it was cool, water signals were more robust. But when the Sun came up and warmed the Moon’s surface by lunar noon, they faded. They strangely intensified again as the temperatures cooled later in the day. This recurring daily change suggests an ongoing process—perhaps one in which solar wind is repeatedly forming and rearranging water molecules on the Moon.
Other Theories on the Table
Although solar wind is the most attractive explanation at this point, scientists have not closed the door to other ideas. One of the alternative theories centers on meteoroid impacts. When meteoroids slam into the Moon, they generate intense heat and pressure, initiating quick chemical reactions that may create water. These impacts are comparatively rare, though, and occur in discrete locations. As a contrast to the constant, worldwide rain of solar wind, meteoroid impacts look less likely to be the principal source of lunar water formation.
The Apollo 17 Sample Experiment
The procedure conducted by NASA researchers Dr. Li Hsia Yeo and Dr. Jason McLain was both sensitive and revolutionary. The researchers employed actual lunar soil samples gathered over 50 years ago when the Apollo 17 mission took place. The samples were stored in tightly sealed containers to prevent any exposure to moisture from planet Earth. In the laboratory, the team began by heating the soil to remove any residual water that may have penetrated over time. They next exposed it to an intense beam of simulated solar wind for several days—essentially condensing what would otherwise be 80,000 years of solar radiation on the Moon into a very brief time period.
Clear Evidence Emerges
Placing the experiment in position was not simple, says McLain. Establishing a space-like setting within a lab and maintaining the purity of the lunar samples was trial and error that took several rounds. But all the effort was worth it. The results were definite chemical shifts in the soil following exposure to solar wind—evidence that the Sun’s charged particles truly could initiate the creation of water and hydroxyl molecules. This provided firm experimental support for the long-standing hypothesis that solar wind is a major source of Moon water.
Future Moon Mission Implications
The results have thrilling implications for future space travel, particularly for future lunar missions such as NASA’s Artemis mission. If water can be generated continuously on the Moon through natural interactions with solar wind, future astronauts may not need to bring all their water from Earth. Rather, they might be able to harvest it from the Moon’s surface—either by heating up the dirt or with specialized equipment to trap the newly created molecules. That would make long-term missions to the Moon more viable and affordable, paving the way for permanent bases on the Moon or even as a stepping stone to Mars.
