Scientists have just made a gigantic discovery on the surface of Mars, and it’s a terrible one that could cripple future plans to find signs of alien life on the Red Planet. Evidence has built up over the years that there was once water on the surface of Mars, creating hope that we might discover evidence of microbiaal life there, but a new study suggests that the soil surface is toxic to bacteria and has created a sterile planet.

Astrobiologists, who are scientists who search for microbial life outside of Earth, new for a while that perchlorates or salt minerals could be found throughout the surface of Mars. Scientists were hopeful that this toxic chemical couldn’t be activated without heat and therefore could remain stable in the Martian soil for hours each summer day, but a new study found that ultraviolet light can active the perchlorate without heat.

That’s a problem, because UV-activated perchlorate kills bacteria within minutes. The scientists’ findings were published in the journal Nature Scientific Reports.

“The environment on Mars may be more harmful to Earth-based life forms than previously thought, experiments by Edinburgh scientists have shown,” the statement from the University of Edinburgh reads. “Researchers investigated the behaviour of chemical compounds, called perchlorates, which are found on the surface of the red planet. They found that, when exposed to UV light whilst in environmental conditions mimicking those on Mars, the chemicals can kill bacteria commonly carried by spacecraft. Their findings could have implications for potential contamination from robotic and human exploration of Mars.”