In December 1972, astronauts Gene Cernan and Harrison Schmitt hammered a hollow metal tube into the surface of the Moon’s Taurus-Littrow Valley and pulled it back out filled with lunar soil. They sealed it. They brought it home. And then, at NASA’s instruction, scientists put it on a shelf — and waited over 50 years for technology to catch up with the question. When researchers finally opened it and analyzed what was inside, they found something that upended a central assumption about the Moon’s relationship to Earth. The Moon’s interior, it turns out, is chemically stranger than we ever believed.
The discovery arrived not from a new mission but from a 53-year-old tube of carefully preserved lunar regolith. It is one of the most striking examples in the history of science of patience as a research strategy — and of what happens when that patience is rewarded.
The Plan Behind the Patience
The Apollo program returned 382 kilograms of lunar material to Earth across six missions between 1969 and 1972. Most of it was analyzed immediately using the best available technology of the era. But a small selection was treated differently. NASA scientists, aware that analytical instruments would inevitably advance, deliberately set aside some samples in pristine, sealed conditions — to be opened only when the technology existed to learn things from them that 1970s-era science simply could not.
The Apollo Next Generation Sample Analysis (ANGSA) initiative was designed to examine these original, untouched samples that were wisely set aside in anticipation of future, greatly evolved investigatory capabilities. Now, 50 years later, modern advanced instrumentation and processes can be applied to learn more than was possible in the Apollo era.
“The agency knew science and technology would evolve and allow scientists to study the material in new ways to address new questions in the future,” said NASA’s Lori Glaze, director of the Planetary Science Division.
Sample 73001 — the sealed lower half of the double drive tube hammered into the Moon by Cernan and Schmitt — was kept in a helium-purged chamber at NASA’s Johnson Space Center in Houston, untouched and unchanged, until researchers were finally ready to open it.
What the Tube Held
A research team led by a Brown University professor analyzed the sulfur isotopes within volcanic material from the sealed drive tube using secondary ion mass spectrometry, a highly precise method of isotope analysis that didn’t exist in 1972 when the samples were first returned to Earth.
Isotopes are variants of the same element that differ slightly in atomic mass. They act as chemical fingerprints. If two rocks share the same isotope ratios, scientists can infer they share a common origin. For decades, one of the foundational assumptions in lunar science was that the Moon and Earth would show matching sulfur isotope signatures. This assumption was rooted in the giant impact hypothesis — the leading explanation for how the Moon formed — which holds that a Mars-sized body called Theia collided with the early Earth roughly 4.5 billion years ago, and that the debris from that collision coalesced into the Moon. Because the Moon is thought to have formed largely from Earth material, its chemical fingerprints were expected to broadly resemble Earth’s.
Sulfur is where that expectation collapsed.
“Before this, it was thought that the lunar mantle had the same sulfur isotope composition as Earth,” said James Dottin, an assistant professor of Earth, environmental, and planetary sciences at Brown and lead author of the study. “That’s what I expected to see when analyzing these samples, but instead we saw values that are very different from anything we find on Earth.”
The finding was so surprising that Dottin’s first reaction was disbelief. “My first thought was, ‘Holy shmolies, that can’t be right,'” Dottin said. “So we went back to make sure we had done everything properly, and we had. These are just very surprising results.”
The analysis of sulfides in regolith particles from the opened Apollo 17 drive tube revealed strongly sulfur-33 and sulfur-34 depleted values, positively correlated in a way that indicates mixing between at least two distinct sources of sulfur in the lunar mantle, one of which is associated with photochemically processed sulfur from a gaseous environment.
In other words, the lunar mantle contains sulfur that does not match what we find anywhere on Earth — and the pattern in that sulfur points toward processes, and potentially a history, that scientists are only now beginning to reconstruct.
Two Explanations, Both Remarkable
The discovery raises a question that researchers cannot yet definitively answer: where did this exotic sulfur come from? Dottin and his colleagues have narrowed the possibilities to two leading hypotheses, each with profound implications for our understanding of the Moon.
The first traces the anomaly to the Moon’s earliest history. Depleted sulfur-33 ratios are found when sulfur interacts with ultraviolet light in an optically thin atmosphere. The Moon is thought to have had a short-lived atmosphere early in its history, which could have supported that kind of photochemistry. If sulfur at the lunar surface was chemically altered by UV radiation in this ancient atmosphere, and that processed material was somehow transported deep into the lunar mantle, it would require explaining a mechanism for moving material from the surface to the interior of a world with no plate tectonics.
“That would be evidence of ancient exchange of materials from the lunar surface to the mantle,” Dottin said. “On Earth, we have plate tectonics that does that, but the Moon doesn’t have plate tectonics. So this idea of some kind of exchange mechanism on the early Moon is exciting.”
The second explanation reaches back even further — to the very origin of the Moon itself. The leading hypotheses for the origin of the Moon call for a giant impact event between proto-Earth and a separate impactor called Theia. The efficiency of mixing material among these two planetary bodies remains a subject of debate. Inefficient mixing during this process could leave behind remnants of the composition of proto-Earth and/or Theia. If Theia had a fundamentally different sulfur isotope composition from Earth, and if the mixing during the Moon-forming impact was incomplete, then the exotic sulfur in the lunar mantle could be a chemical relic of Theia itself — preserved, untouched, inside the Moon for 4.5 billion years.
Both possibilities are scientifically extraordinary. One rewrites the story of the early Moon’s geological activity. The other sheds new light on the solar system’s most formative collision event.
Why Sealed Samples Change Everything
The precision of this discovery depended entirely on the sealed condition of the samples. Lunar soil exposed to terrestrial air and moisture over decades becomes contaminated — its chemical signatures scrambled by interaction with Earth’s atmosphere. The ANGSA samples, stored in helium and never exposed to Earth’s environment, retained exactly what they captured on the Moon in 1972.
“We’ve learned so many lessons from these samples about how to preserve, store and open lunar material without damaging the contents. This is already feeding into plans for Artemis’ science and helping to develop new instruments,” said Giulia Magnarini, a researcher involved in the analysis.
The technique Dottin used — secondary ion mass spectrometry — can measure isotope ratios at the scale of individual microscopic grains within the sample. It is, in essence, a way of reading chemical history written at atomic resolution. That capability simply did not exist when Apollo 17 returned to Earth. The instrument that unlocked this discovery had not been invented yet when Cernan and Schmitt sealed the tube.
This means the sulfur signal likely comes from the Moon’s interior, not just surface contamination. The samples were opened under NASA’s ANGSA program, allowing researchers to use tools that didn’t exist in the 1970s.
What Comes Next
The study, published in the Journal of Geophysical Research: Planets in September 2025 under the title “Endogenous, yet Exotic, Sulfur in the Lunar Mantle,” opens more questions than it closes — which, in science, is the mark of a genuinely significant result.
Dottin hopes that future studies, including comparisons with samples from Mars and other planetary bodies, will help resolve the mystery. Understanding these isotope patterns could offer new clues about how the Moon and the rest of the solar system came to be.
Crucially, ANGSA samples are still being released to researchers through NASA’s competitive application process. Additional sealed Apollo material remains at Johnson Space Center, waiting for the next generation of questions and the instruments to answer them. NASA’s Artemis program, which aims to return humans to the lunar south pole, will eventually bring back new samples from previously unexplored regions — samples that will be analyzed not just with today’s technology but with whatever tools exist in the decades ahead.
The lesson of sample 73001 is that the most powerful scientific instrument is sometimes simply time — combined with the wisdom to preserve something in pristine condition until the right question arrives.
Fifty-three years ago, two astronauts on the final lunar landing drove a tube into the Moon and trusted that future scientists would know what to do with it. They were right.
