NASA scientists have discovered that the solar wind, a stream of charged particles, enriches the Moon’s surface with elements that could produce water when it slams upon it at 450 kilometers per second (or about 1 million miles per hour).
Scientists used computer software to mimic the chemical reactions that take place when the solar wind strikes the Moon’s surface. They discovered that protons sent to the Moon interact with the surface’s electrons to create hydrogen (H) atoms.
The plentiful oxygen (O) atoms bonded in silica (SiO2) and other oxygen-bearing molecules that make up the lunar soil, or regolith, are then attracted by these atoms as they travel across the surface and latch onto them. Hydrogen and oxygen combine to form the hydroxyl (OH) molecule, which is a part of water, or H2O.
“We think of water as this special, magical compound,” said William M. Farrell, a plasma physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who helped develop the simulation. “But here’s what’s amazing: every rock has the potential to make water, especially after being irradiated by the solar wind.”
For NASA to send people to the Moon and establish a permanent presence there, it is essential to know how much water or its chemical components are present there, said Orenthal James Tucker, a physicist at Goddard who spearheaded the simulation research.
“We’re trying to learn about the dynamics of transport of valuable resources like hydrogen around the lunar surface and throughout its exosphere, or very thin atmosphere, so we can know where to go to harvest those resources,” said Tucker, who recently described the simulation results in the journal JGR Planets.
We think of water as this special, magical compound. But here’s what’s amazing: every rock has the potential to make water, especially after being irradiated by the solar wind.
William M. Farrell
The chemistry of the Moon’s surface was determined by several spacecraft using infrared detectors that measure light emitted from the Moon. These include India’s Chandrayaan-1, which orbited the Moon a decade ago, the NASA Cassini spacecraft, which crossed the Moon on its way to Saturn, and the Deep Impact mission, which had several close calls with the Earth-Moon system on its approach to comet 103P/Hartley 2.
Every discovered indication of water or its components (hydrogen or hydroxyl). However, it is still unclear how these atoms and molecules develop on the Moon. The required chemical processes may be started by meteor impacts, but many scientists think that solar wind is the main force.
The solar wind theory is supported by Tucker’s simulation, which follows the lifecycle of hydrogen atoms on the Moon.
“From previous research, we know how much hydrogen is coming in from the solar wind, we also know how much is in the Moon’s very thin atmosphere, and we have measurements of hydroxyl in the surface,” Tucker said. “What we’ve done now is figure out how these three inventories of hydrogen are physically intertwined.”
Understanding why spacecraft have discovered variations in the amount of hydrogen in various regions of the Moon required demonstrating how hydrogen atoms behave on the moon.
The scientists came to the conclusion that less hydrogen accumulates in warmer locations, such as the equator of the Moon, because hydrogen atoms deposited there are powered by the Sun and swiftly outgas from the surface into the exosphere. On the other hand, because there is less Sun radiation and the outgassing is inhibited, it looks that more hydrogen is accumulating in the colder surface near the poles.
Overall, Tucker’s simulation demonstrates that the solar wind’s continuous blasting of the Moon’s surface causes the silicon, iron, and oxygen atoms that make up the majority of the soil to become loosely bound together. As a result, the bonds between oxygen atoms are incomplete.
Hydrogen atoms temporarily become caught with the out-of-balance oxygen as they move across the Moon’s surface (longer in cold regions than in warm). Before ultimately dissipating into the Moon’s atmosphere and ultimately into space, they drift from O to O.
“The whole process is like a chemical factory,” Farrell said.
According to Farrell, one important implication of the finding is that every exposed body of silica in space, from the Moon to a tiny dust grain, has the ability to produce hydroxyl and so turn into a water-producing chemical factory.
