Humans are inching closer to living beyond Earth, but sustaining life on the moon or Mars requires a critical resource: water.
A team from UC San Diego is helping to identify lunar water sources, aiding NASA’s Artemis mission in its quest to explore and eventually colonize the moon. By analyzing lunar rocks, researchers uncovered that most of the moon’s water is either native or comes from comet impacts, debunking the idea that solar winds played a major role.
Unlocking the Moon’s Water Secrets
As humanity looks toward a future beyond Earth — on the Moon, Mars, and beyond — one of the biggest challenges is securing the essentials for survival: oxygen, food, and water. Scientists know water exists on the Moon, but pinpointing its exact location is crucial. Is it hidden in craters, trapped in permanently shadowed regions, or concentrated at the poles? Identifying these water sources is key to supporting long-term lunar habitation — something that, until now, has belonged to the realm of science fiction.
Researchers from the University of California San Diego are working to change that by helping guide future space missions, including NASA’s Artemis program, which aims to explore and eventually establish a human presence on the Moon. Their research, featured in a special issue of Proceedings of the National Academy of Sciences (PNAS) titled “Water on the Moon and Mars,” could serve as a roadmap for lunar exploration. The cover of this issue even highlights Artemis I, the first step in NASA’s ambitious lunar initiative.
Among the scientists contributing to this research is the father-son team of Mark Thiemens, a Distinguished Professor of Chemistry and Biochemistry at UC San Diego, and Maxwell Thiemens, a research fellow at Vrije Universiteit Brussel and an alumnus of Scripps Institution of Oceanography. Their work brings us closer to understanding the Moon’s water sources, a critical step in turning lunar exploration into a long-term reality.
A Legacy of Lunar Exploration
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.
Did You Know?
The most widely accepted theory states that about 4.5 billion years ago there was a collision between the Earth and another planet. The debris from this impact collected in an orbit around Earth to form the moon.
NASA’s Apollo space missions took place from 1961 to 1972, and culminated with the first moon landing in 1969. All told, the Apollo astronauts brought back 842 pounds of moon rock, some of which made its way to Harold Urey’s lab at UC San Diego.
The goal of NASA’s Artemis campaign is to explore the moon for scientific discovery, and to learn how to live on another world as they prepare for a human mission to Mars. Artemis I was an unmanned test flight around the moon, while Artemis IV will debut humanity’s first lunar space station.
The permanently shadowed regions of the moon never see sunlight. Because the axis of the moon is nearly perpendicular to the direction of the sun, some areas at the moon’s poles have remained in darkness for over two billion years.
Extracting Water from Lunar Rocks
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.
Lunar Water Origins: What the Data Reveals
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.”
Moon vs. Mars: A Glimpse Into the Future
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.”
The Next Step: Extraction and Utilization
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.
Reference: “Triple oxygen isotopes of lunar water unveil indigenous and cometary heritage” by Maxwell M. Thiemens, Morgan H. Nunn Martinez and Mark H. Thiemens, 16 December 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2321069121
Full list of authors: Maxwell Thiemens (Vrije Universiteit Brussel), Morgan Nunn Martinez and Mark Thiemens (both UC San Diego).
This research was supported, in part, by the NASA Earth and Space Science Fellowship, the Zonta International Amelia Earhart Fellowship, and the Achievement Rewards for College Scientists Fellowship.
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