The presence of ice in the permanently shadowed craters around the Moon's poles has been known for some time. However, researchers had been unsure if the hydration detected on the satellite's sunlit areas was "molecular" water (H2O), or hydroxyl (OH), a molecule that's one hydrogen atom shy of becoming water. On October 26, 2020, NASA confirmed that the liquid was indeed water.
“We had indications that H2O – the familiar water we know – might be present on the sunlit side of the Moon,” said Paul Hertz, Director of Astrophysics at NASA. “Now we know it is there. This discovery challenges our understanding of the lunar surface and raises intriguing questions about resources relevant for deep space exploration.”
The discovery was made using data collected by NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). The modified Boeing 747 aircraft, which can fly its large telescope at altitudes of up to 45,000 feet, allows researchers to clearly observe space objects. The water molecules — detected using a special infrared camera capable of discerning between the wavelengths of H2O and OH — were found in the Clavius Crater. Located on the Moon's Southern Hemisphere, the large crater can be clearly seen from Earth.
However, before you start packing your bags for our satellite, be warned that the water concentration is extremely low — about 100 to 412 parts per million. To put it in perspective, the Sahara Desert has about 100 times more water! "This is not puddles of water but instead water molecules that are so spread apart that they do not form ice or liquid water," said NASA researcher Casey Honniball, who led the study. Though not enough to sustain humans, the discovery is significant because water is a rare and precious resource in deep space.
The scientists speculate that the H2O molecules may have been deposited by the tiny meteorites that are continually bombarding the Moon's surface. Another plausible explanation involves a multi-step process where the Sun's solar wind brings hydrogen to the Moon, which then reacts with oxygen-bearing minerals in the soil to create hydroxyl. This hydroxyl could later be transformed into water from the micrometeorites' radiation.
Also perplexing is how the water escapes evaporation. The liquid could be trapped in tiny bead-like structures in the soil that form from the intense heat generated from the micrometeorite impacts. Alternatively, the H2O molecules may be hidden inside the lunar soil grains and sheltered from the Sun.
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Honniball. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
NASA plans to conduct follow-up missions to determine how widespread the water is across the lunar surface. The findings will allow the US space agency to find the perfect landing for its Artemis mission that will take the first woman and next man to explore the Moon more extensively in 2024.
Resources: Space.com, NASA.gov