A study published in Nature Communications has shown that asteroid impacts were responsible for depositing the majority of the water found within the lunar surface. An international team of scientists analyzed the data taken from a 2008 joint mission between NASA and India’s space agency and found that while the majority of the water on the moon came from asteroids and not comets, an estimated that 20% of the moon’s water is still believed to have come from comets due to the presence of deuterium, a hydrogen isotope commonly found in comets.
During a period known as the lunar cataclysm, a high number of asteroids impacted with celestial bodies throughout our solar system. The study posits that asteroids collided with the moon between 4.5 and 4.3 billion years ago and left “carbonaceous chondrite-type materials” that led to the formation of water molecules. The article claims that that the majority of lunar water was left by asteroid impacts during this period:
To a first order, a dominantly asteroidal source of water accreted during the [lunar cataclysm] is similar to the dominant source inferred for the subsequent basin-forming epoch of the Moon, based on geochemical, and mineralogical markers, implying that asteroids and not comets dominated the impactor population hitting the Moon during its first 500 million years of geological history.
After the Apollo missions failed to find any concrete evidence of water in lunar soil samples, it was thought that our moon was completely devoid of water. In the years following, however, spectrographic tests from India’s first expedition to the moon determined that lunar soil from within shadowy craters and polar regions contained molecules that could only be due to the presence of water.
NASA is already eyeing a number of methods for mining the moon’s surface and extracting lunar water to help with Earth’s dwindling clean water supply and deep space exploration. Long-range space missions such as the proposed upcoming Mars missions will need large sources of water to sustain astronauts. Due to the weight of liquid water, it would be impossible to simply bring sufficient water supplies for a multi-year voyage; thus, the need for developing methods for extracting extraterrestrial water is a great one.
It might not be NASA doing most of the water mining, however. A 2015 law known as the Spurring Private Aerospace Competitiveness and Entrepreneurship Act, or SPACE Act, made it legal for private U.S. citizens and companies to “engage in the commercial exploration and exploitation of ‘space resources,’” but luckily excludes biological life and matter. So, while we might be mining water in space soon, that water might unfortunately be resold to us in overpriced, commercially-branded bottled form. Oh, dystopian corporate future, don’t ever change.