Introduction
Since man originally landed on the moon 40 years ago, scientists have believed the Moon was dry. Until recently, four different spacecraft have proven the existence of water on the Moon. The existence of water on the Moon brings about many questions, which have just recently been looked into. This webpage will provide a brief history of water on the Moon and how it is believed to have gotten there.
Apollo's Discoveries
When Apollo astronauts returned from the Moon 40 years ago, they brought back several samples of lunar rocks. These rocks were analyzed for signs of water bound to minerals in the lunar rocks. While trace amounts of water were detected in the lunar rocks, scientists assumed the rocks had been contaminated from Earth because the containers in which the rocks were carried had leaked. Also adding to the confusion, isotopes of oxygen that exist on the Moon are the same as those that exist on Earth, so it is nearly impossible to tell the difference between water from the Moon and water from Earth. After the Apollo missions, scientists continued to suspect that water ice deposits could only be found in the coldest spots of the Moon’s south pole craters that never saw sunlight. However, four separate missions which studied the Moon after Apollo have proven otherwise.
Spacecrafts Confirming Water on the Moon
Chandrayaan 1 (India’s first-ever moon probe) was launched in October of 2008. This probe was aimed at mapping the lunar surface and determining its mineral composition. Its NASA-built “Moon Mineralogy Mapper,” also known as M3, detected wavelengths of light reflected off the surface which signaled the chemical bond between hydrogen and oxygen. This indicates either the presence of water or hydroxyl (a hydrogen and an oxygen bound together). M3 could only penetrate the top few millimeters of lunar surface, which means the water detected is at or near the lunar surface. M3 also observed that the water signal is stronger toward the moon’s two poles. This image from the probe is to the right.
The Cassini probe confirmed that this discovery was actually correct. Another interesting thing that Cassini confirmed was that there was actually distribution of water across the whole Moon, more being distributed near the poles and less in the lunar maria.
Deep Impact, a NASA space probe launched in January of 2005, had the mission of studying the composition of a comet, but with its multiple passes of the Moon, Deep Impact was able to observe the same regions at different times of the lunar day. At noon, when the sun's rays were strongest, the water feature was lowest. The water feature was strongest during the lunar morning.
A probe, LCROSS, and an additional rocket, Centaur, were purposefully crashed onto the surface of the Moon, making impact on October 9, 2009. They landed in the crater Cabeus near the Moon’s South Pole, creating a plume of dust for scientists to study. Here is where the sensing satellite discovered about 25 gallons of water. While the discovery is said to be significant for further exploration of the lunar crater, it is said to mean “practically nothing” to future plans of inhabiting the Moon. The water discovered is suspected simply to be “water clinging to the soil particles,” not a “big reservoir.”
Where did Lunar Water Come From?
When looking at how lunar water came to be, we look at two possible solutions. The first would be a result of icy comets striking the Moon and leaving behind its icy debris. The second would be water that actually originated on the Moon. This water that has its source on the moon may arise from the interaction of the solar wind with moon rocks and lunar soil. The rocks and soil that make up the lunar surface are about 45% oxygen. The solar winds (constant stream of charged particles emitted by the Sun) are mostly protons, or positively charged hydrogen ions. If the hydrogen ions strike the lunar surface with enough force, they may break apart oxygen bonds in the lunar surface. Where free oxygen and hydrogen exist, it is very likely that trace amounts of water will form. Many researchers also suggest that the daily dehydraton and rehydration of the lunar water across the surface could lead to the migration of hydroxyl and hydrogen towards the poles, where it can become permanently trapped in shadowed regions. Although these are the two most feasible explanations of the origin of water on the Moon, we are still unsure.
Conclusion
Over the past ten years, we have discovered that water does indeed exist on the Moon. However, we do not know too much more than this as of now. The recent LCROSS mission was a big step in the studying of this remarkable subject. "The full understanding of the LCROSS data may take some time. The data is that rich," said Anthony Colaprete, LCROSS project scientist and principal investigator at NASA's Ames Research Center. "Along with the water in Cabeus, there are hints of other intriguing substances. The permanently shadowed regions of the moon are truly cold traps, collecting and preserving material over billions of years." It appears we will learn much more about our planet's moon in the years to come.