NASA claims to have found evidence of liquid water on Mars. If true, you’d expect the US government to scramble to set up a new mission to test the claim. After all, discovering that Mars has life or even that in can support life will be one of the greatest discoveries ever.

But that won’t happen so quick. NASA’s press statement makes it seem that scientists have certain evidence of flowing water. They do not. What they have is chemical evidence that gives a strong suggestion of liquid water mixed with salts. More importantly, however, even if NASA was 100% certain that there is liquid water on Mars, it could not do anything about it.

The world’s space powers are bound by rules agreed to under the 1967 Outer Space Treaty that forbid anyone from sending a mission, robot or human, close to a water source in the fear of contaminating it with life from Earth.

Terrestrial life has been shown to be very resilient. Microbes are found in almost every nook and cranny of this planet, even the driest and hottest parts. Earth’s microbes survived nearly two years stuck on the outside of the International Space Station. All probes that land on Mars are cleaned to be sterilized of life but no one yet knows how strict you need to be to ensure that bacterial life cannot form viable, self-sustaining colonies on Mars.

All space missions to an alien world are bound by planetary protection protocols. On Mars, these protocols determine which areas a mission can and cannot land, and how far it can explore after landing. And the more we learn about Mars, as a 2014 report makes it clear, the more special regions are being found where we can’t send missions.

Areas that are warm or wet enough to support Martian life are out of bounds. Polar ice caps, caves, and regions with volcanic activity are such special regions. Even regions where ice is found as deep as five meters below the surface are on the list.

And even that won’t cover all eventualities. The Mars 2020 Rover, for instance, carries a plutonium-powered heat generator, which can, if it falls on the surface, cause ice deep inside to melt and create liquid water. Its exploration area, then, is further restricted. The irony is that all these restrictions mean NASA has to stay away from the very regions where it may find water or Martian life.

NASA’s hype around the discovery of liquid water on Mars can be explained by its constant need to increase funding for its work. And that attention seems to be helping. But it won’t be eager to tell you that its human mission, currently planned for 2030, will inevitably contaminate Mars with microbes, and break the rules of an international treaty.

Indeed, what’s the guarantee that all those objects and rovers we’ve sent to Mars haven’t already contaminated the red planet?