In 2015 NASA announced that they found definitive evidence of liquid water on Mars. But while obtaining a physical sample would revolutionize science, it’s forbidden by international law. 

The Outer Space Treaty of 1967 prevents every nation on Earth from sending a mission, robot or human, close to a water source in the fear of contaminating it with life from Earth [PDF]. In its 140-million-mile journey from Earth to Mars, it’s possible that Curiosity has carried harmful microbes all the way from home. Even though NASA tries its best to sterilize all space-traveling equipment before launch by subjecting it to intense ultraviolet light, it still might harbor microbial hitchhikers.

In theory, NASA could turn up the heat and radiation to a level pretty much guaranteed to destroy any microbial life—but that could also end up wiping out the rover’s internal systems. "In order to be completely sterile, they'd have to use really powerful ionizing radiation or heat, both of which would damage the electronics,” University of New South Wales astrobiologist Malcolm Walter told Fairfax Media. "So they go as far as they dare."

Another issue that would prevent Curiosity from investigating the water source is the terrain itself. The slopes where the streaks formed are steep and therefore difficult to navigate. Future Mars rovers could be designed with this hurdle in mind, and they could also come equipped with DNA sequencers to test for life or 3D-printing capabilities to build smaller bots with little to no chance of being contaminated.

NASA/JPL/University of Arizona

Unfortunately, it’s too late for NASA modify the next generation of Mars rovers, which is set to launch in 2020. The European Space Agency says it plans to send an organic molecule analyzer on its 2018 ExoMars mission, though they still wouldn’t be able to test Martian water unless they could guarantee 100 percent sterilization.

[h/t: Science Alert]