The report this week that definitive signs of water have been detected on Mars immediately set off speculation about finding life on that planet. Which raises an interesting conundrum: How best to explore the damp areas on Mars without contaminating them with microbes carried there from Earth.

The National Aeronautics and Space Administration said on Monday that instruments aboard a spacecraft orbiting Mars had detected signs of hydrated salts at four locations. The salts almost certainly have been hydrated by liquid water in recent days. The water was not standing in pools, but was more like streaks of wet soil. NASA officials described the streaks as evidence that “water — albeit briny — is flowing today on the surface of Mars.”

Since liquid water is essential to life on Earth, the findings raised hopes that microscopic life might be found in the four locations or others like them scattered over Mars. The problem is that NASA’s two active rovers currently on Mars are not thoroughly sterilized and the next rover, scheduled to launch in 2020, will not be sterile, either. There is a danger that they might harbor microbes from Earth that could spread to the Martian surface and confuse further efforts to distinguish Martian life-forms from those of Earth.

The space-faring nations of the world have long followed strict treaty-required procedures to protect planets, moons, comets and asteroids from contamination by Earth life. On Mars ”special regions” have been designated as needing protection because terrestrial organisms are likely to propagate there or Martian life-forms may exist. It may not be easy to keep those areas pristine given how little is known about how life propagates.