Over the course of the past few decades, our ongoing exploration the Solar System has revealed some surprising discoveries. For example, while we have yet to find life beyond our planet, we have discovered that the elements necessary for life (i.e organic molecules, volatile elements, and water) are a lot more plentiful than previously thought. Case in point, in the 1960’s, it was theorized that water ice could exist on the Moon; and by the next decade, sample return missions and probes confirmed this.
Since that time, a great deal more has been discovered, largely around the permanently shadowed craters in the polar regions. This in turn has led to a debate within the scientific community as to where the water came from. Was it the result of in-situ production, or was it delivered to the surface by water-bearing comets, asteroids and meteorites? According to a recent study produced by a team of scientists from the UK, US and France, the majority of the Moon’s water appears to have come from asteroids impacting on the surface.
For the sake of their study, which appeared recently in Nature Communications, the international research team examined the samples of lunar rock and soil that were returned by the Apollo missions. When these samples were originally examined upon their return to Earth, it was assumed that the trace of amounts of water they contained were the result of contamination. The Moon, it was widely believed, was bone dry.
However, a 2008 study revealed revealed that samples of volcanic glass beads contained water molecules (46 parts per million), as well as various volatile elements (chlorine, fluoride and sulfur) that could not have been the result of contamination. This was followed up by the deployment of the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater Observation and Sensing Satellite (LCROSS) in 2009, which discovered abundant supplies of water around the southern polar region,
However, that which has been discovered on the surface pales to the water that has since been discovered beneath it. Evidence of this interior water was was discovered by the USRO’s Chandrayaan-1 lunar orbiter – which carried the NASA’s Moon Mineralogy Mapper (M3) and delivered it to the surface. Analysis of this data has showed that the Moon’s interior sources of water are considerably more abundant than what the surface holds.
But the question remained, where did it all come from? That is what Dr. David A. Kring and his colleagues set out to answer. By examining data provided by the Apollo missions, they examined the ratios of hydrogen to deuterium (aka. “heavy hydrogen”) and compared these to isotope rations of known comets. As Dr. Kring told Universe Today via email:
“The current study utilized analyses of lunar samples that had been collected by the Apollo astronauts, because those samples provide the best measure of the water inside the Moon. We compared those analyses with analyses of meteoritic samples from asteroids and spacecraft analyses of comets.
From their comparisons between lunar rock and known comets, they determined that a combination of primitive meteorites (carbonaceous chondrite-type) were responsible for the majority of water to be found in the Moon’s interior today. In addition, they concluded that these types of comets played an important role when it comes to the origins of water in the inner Solar System.
The presence of water on the Moon has always been a source of excitement, particularly to those who hope to see a lunar base established there someday. But by knowing the source of that water, we can come to learn more about the history of the Solar System and how it came to be. It will also come in handy it comes time to search for other sources of water, which will always be a factor when trying to establishing outposts and even colonies throughout the Solar System.