Scientists are gearing up for a new wave of lunar exploration, but a study published in the Journal of Geophysical Research: Planets suggests every landing could leave behind more than just footprints. Researchers found that methane from spacecraft exhaust can spread across the moon in days, potentially contaminating ancient ice that holds clues about how life began on Earth.

Using computer simulations based on the European Space Agency's Argonaut mission, the team modeled how methane, the main organic compound from propellant combustion, would travel after a South Pole landing. The results were sobering: methane reached the North Pole in less than two lunar days (about two Earth months), and within seven lunar days (nearly seven Earth months), over half of the released methane was trapped in cold polar regions - 42% at the South Pole and 12% at the North Pole.

“The timeframe was the biggest surprise,” said Silvio Sinibaldi, ESA’s planetary protection officer and senior author. “In a week, you could have distribution of molecules from the South to the North Pole.” The moon’s near-vacuum allows molecules to hop ballistically across the surface, meaning no landing site is truly safe. “Wherever you land, you will have contamination everywhere,” warned lead author Francisca Paiva, a physicist at Instituto Superior Técnico.

The stakes are high: permanently shadowed craters at the poles contain ice that may preserve prebiotic organic molecules - the chemical precursors to life, including DNA components - delivered by comets billions of years ago. Earth’s churning surface has erased such evidence, but the moon’s frozen vaults remain pristine - unless we muck them up with our own exhaust.

Sinibaldi and Paiva stress that contamination isn’t inevitable. Colder landing sites might keep exhaust more localized, and exhaust molecules may only coat the surface, leaving deeper ice intact. But they urge mission teams to add instruments that can validate these models. “We will miss an opportunity if we don’t have instruments on board,” Sinibaldi said. Paiva also plans to study other contaminants, like paint and rubber particles. “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.”