As humankind imagines living off-planet — on the moon, Mars and beyond — the question of how to sustain life revolves around the physical necessities of oxygen, food and water. We know there is water on the moon, but how do we find it? Is it in the craters? The shadowed regions? The poles? Knowing where to look gives astronauts the best chance at successfully living on the moon, something that has, heretofore, remained the stuff of science fiction.
Researchers from the University of California San Diego may help bring science fiction to reality by providing a divining rod to guide future space missions, including NASA’s Artemis campaign, which seeks to explore and, eventually, inhabit the moon. Their work appears in a special issue of Proceedings of the National Academy of Sciences (PNAS) called “Water on the Moon and Mars,” which features Artemis I on its cover.
The researchers included the father-son team of Mark Thiemens, UC San Diego Distinguished Professor of Chemistry and Biochemistry, and Maxwell Thiemens, a research fellow at the Vrije Universiteit Brussel, who is also an alumnus of Scripps Institution of Oceanography.
In 1967, Nobel laureate Harold Urey and James Arnold — both faculty members in UC San Diego’s Department of Chemistry — were among the first to receive Apollo 11 lunar samples. Urey was one of the first scientists to theorize that there was water on the moon, particularly in the permanently shadowed regions of the moon’s poles. Today, scientists believe that water on the moon originated from one of three sources:
- indigenous to the moon,
- created by solar winds (where hydrogen from the sun reacts with oxygen at high energy on the moon and likely Mars to create water)
- deposition (from icy comets that have crashed onto the lunar surface).
On Earth, human civilizations often bubble up near bodies of water and it would be no different in space. On the moon, it’s important to know the origin of the water sources because it will give astronauts guidance on where it would be most prudent to set up bases and habitats.
To learn about the origin of water on the moon, Morgan Nunn Martinez (who was a UC San Diego graduate student at the time) extracted very small amounts from lunar rocks collected from the 1969 Apollo 9 mission. It may sound implausible to get water from a rock, but it is possible through “thermal release,” a process where lunar samples were heated to 50, 150 and 1,000 degrees Celsius (122, 302, and 1,832 degrees Fahrenheit respectively). As it turns out, these rocks were surprisingly “wet.”
The lowest temperatures released lightly bound water molecules — those molecules that are attached to other molecules (in this case, lunar rock) through a weak attraction. At 1,000 degrees Celsius, tightly bound water molecules, which are more deeply embedded in the rock, were released.
Through this process, gas water molecules are collected, then purified so that only the oxygen remains. The team then measured the composition of three different oxygen isotopes.
Isotopes are atoms of the same element that have varying numbers of neutrons, which changes their mass — the more neutrons, the heavier the atom. These measurements are particularly useful in determining a substance’s origin and age.
Think of it like space forensics. In the way humans have unique fingerprints, astronomical objects, like comets and the sun, have unique signatures. Scientists are able to look at the oxygen isotope measurements and determine the origin of the water.
Their data revealed that most of the lunar water likely originated from the moon itself or from comet impacts. Contrary to popular belief, solar winds did not significantly contribute to the moon’s water stores.
“What’s nice about this research is that we’re using the most advanced scientific measurements and it supports common sense ideas about lunar water — much of it has been there since the beginning and more was added by these icy comet impacts,” stated Maxwell Thiemens. “The more complicated method of solar wind-derived water doesn’t appear to have been that productive.”
Although not a main thrust of the paper, the researchers also measured samples from Mars. If NASA’s Artemis program is able to successfully colonize humans on the moon, it would bode well for the ultimate mission of inhabiting Mars.
“This kind of work hasn’t been done before and we think it can provide NASA with some valuable clues about where water is located on the moon,” stated Mark Thiemens. “The real goal of Artemis is to get to Mars. Our research shows that likely there is at least as much water on Mars as on the moon, if not more.”
Of course, locating the water is only the first step. Being able to extract it from lunar rocks and soil in quantities large enough to sustain life will require further technological advancements and discovery.
Full list of authors: Maxwell Thiemens (Vrije Universiteit Brussel), Morgan Nunn Martinez and Mark Thiemens (UC San Diego).
This research was supported, in part, by a NASA Earth and Space Science Fellowship, a Zonta International Amelia Earhart Fellowship and the Achievement Rewards for College Scientists Fellowship.
