Scientists are worried about pollution from exhaust fumes from lunar landers taking off or landing on the Moon.
Moon Photo: Photo by nousnou iwasaki on Unsplash
The issue has been raised in a new study by scientists at the Johns Hopkins Physics laboratory in the US.
They found that the fumes from a lunar lander can quickly spread around the Moon in just three hours.
Some can stay in the Moon's thin atmosphere for two months.
They worry that the exhaust could also contaminate some things that scientists want to study - like ice believed to be sitting in the Moon's craters.
And the scientists say this could be an issue as more countries set their sights on sending exploratory craft to the moon.
In a statement, one of the researchers Parvathy Prem said the impact of the exhaust mattered less during the Apollo missions but could have greater effect now.
Astronauts on Apollo missions to the Moon mostly collected rock samples which were less affected.
But NASA's Artemis programme of flights to the Moon has collected ice samples as a prime objective - and the exhaust could coat the ice.
"These are some of the only places where we can find traces of the origin of water in the inner solar system," Prem said.
Frozen exhaust on the ice could confound scientific measurements, Prem said.
A co-author on the study, planetary scientist Dana Hurley said the residue exhaust would eventually fade away but could significantly coat the lunar surface up to 100km from a landing site, and spread around the Moon.
"The interesting thing about Parvathy's work is that it shows very well that the effect, while small and temporary, is global."
The news comes as several countries are engaged in returning to the Moon. NASA's Artemis programme aims to land two astronauts near the Moon's south pole by 2023.
The European Space Agency has said that it wants to investigate building a settlement on the Moon - dubbed a "moon village". And China is in the midst of a lunar exploration programme using robots, landers and rovers.