NASA is planning its first-ever mission to bring dirt and rocks from Mars back to Earth — but what if the samples contain alien pathogens and they escape into the Earth’s atmosphere? The space agency said it’s collaborating with the European Space Agency to figure out exactly how to protect our home planet from any alien microbes that might hitch a ride.

Scientists say that anything that has contacted Mars directly will be contained or sterilized before it is returned. But the danger of a rupture or leak is still a real possibility. They claim that the potential hazard of bringing Mars samples to earth is very low. But, what if they are wrong?