Methane released in exhaust could move from one lunar pole to the other in less than two lunar days, with roughly half of it eventually depositing in areas that may preserve the original chemical building blocks linked to the emergence of life on Earth.
Over half of the methane released in exhaust from lunar landers could spread into regions of the moon that may otherwise preserve evidence related to the origins of life on Earth, according to a new study. The researchers found that this contamination could happen quickly no matter where a spacecraft lands. Even a mission touching down at the South Pole could release methane molecules that “hop” across the lunar surface and reach the North Pole in less than two lunar days.
With renewed interest in lunar exploration from governments, private companies, and non-governmental organizations, the authors emphasize the growing need to understand how these missions might affect future scientific research. Insights like these could guide planetary protection efforts for the moon and help shape mission designs that limit environmental disturbance and protect valuable scientific records.
The research was published in Journal of Geophysical Research: Planets, AGU’s journal for original research in planetary science.
“We are trying to protect science and our investment in space,” said Silvio Sinibaldi, the planetary protection officer at the European Space Agency and senior author on the study. The moon is a natural laboratory ripe for new discoveries, he said — but, paradoxically, “our activity can actually hinder scientific exploration.”
Ancient Ice and the Origins of Life
Near the moon’s poles, craters that never receive sunlight (called permanently shadowed regions) contain ice that may trap material delivered to both the moon and Earth by comets and asteroids billions of years ago. Scientists believe this frozen material could include “prebiotic organic molecules,” which are chemical components that, under the right conditions, may have formed the earliest building blocks of life, including DNA. Discovering these molecules in an unchanged state could offer rare insight into how life began on Earth.
“We know we have organic molecules in the solar system — in asteroids, for example,” Sinibaldi said. “But how they came to perform specific functions as they do in biological matter is a gap we need to fill.”
On Earth, geological activity and erosion have likely erased direct evidence of what these ancient molecules once looked like.
The moon, however, has regions that have remained largely unchanged for billions of years. This is especially true in permanently shadowed regions, where extreme cold slows molecular motion and allows substances to accumulate over time. The concern, researchers note, is that exhaust from spacecraft could also become trapped in these same locations, potentially masking or altering some of the most pristine clues to life’s origins.
A molecular mad dash
Sinibaldi and Francisca Paiva, a physicist at Instituto Superior Técnico and lead author of the study, built a computer model to simulate how that contamination might play out, using the European Space Agency’s Argonaut mission as a case study. The simulations focused on how methane, the main organic compound released during combustion of Argonaut propellants, might spread across the lunar surface during a landing at the moon’s South Pole. While previous studies had investigated how water molecules might move on the moon, none had done so for organic molecules like methane. The new model also accounted for how factors like solar wind and UV radiation would impact the methane’s behavior.
“We were trying to model thousands of molecules and how they move, how they collide with one another, and how they interact with the surface,” said Paiva, who was a master’s student at KU Leuven and an intern at the European Space Agency during the research. “It required a lot of computational power. We had to run each simulation for days or weeks.”
The model showed exhaust methane reaching the North Pole in under two lunar days. Within seven lunar days (almost 7 months on Earth), more than half of the total exhaust methane had been “cold trapped” at the frigid poles — 42% at the South Pole and 12% at the North.
“The timeframe was the biggest surprise,” Sinibaldi said. “In a week, you could have distribution of molecules from the South to the North Pole.”
Why the Moon Spreads Contamination So Easily
That’s partly because the moon has almost no atmosphere of other molecules to bump into. Impeded only by gravity, methane molecules on the moon bound freely across the landscape like bouncy balls across an empty room, energized by sunlight and slowed by cold.
“Their trajectories are basically ballistic,” Paiva said. “They just hop around from one point to another.” That’s concerning, she explained, because it means there may be no foolproof landing sites anywhere. “We showed that molecules can travel across the whole moon. In the end, wherever you land, you will have contamination everywhere.”
That doesn’t mean there’s nothing to be done to minimize contamination. Colder landing sites, Paiva noted, might still corral exhaust molecules better than warmer ones. There might also be ways around the contamination: Sinibaldi wants to study whether exhaust molecules might simply settle on the icy surfaces of PSRs, leaving material underneath unscathed for research.
Above all, the duo said, the results need confirmation from both additional simulations and real-life measurements on the moon. “I want to bring this discussion to mission teams, because, at the end of the day, it’s not theoretical — it’s a reality that we’re going to go there,” Sinibaldi said. “We will miss an opportunity if we don’t have instruments on board to validate those models.”
Paiva hopes to study whether molecules other than methane, including those in spacecraft hardware like paint and rubber, might also pose risks to research.
“We have laws regulating contamination of Earth environments like Antarctica and national parks,” she said. “I think the moon is an environment as valuable as those.”
Reference: “Can Spacecraft-Borne Contamination Compromise Our Understanding of Lunar Ice Chemistry?” by Francisca S. Paiva and Silvio Sinibaldi, 13 November 2025, Journal of Geophysical Research: Planets.
DOI: 10.1029/2025JE009132
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