The results of NASA’s 1976 Viking lander missions were largely inconclusive. But, what if our spacecraft brought tiny forms of Earth life to Mars? Could it have survived there? If so, what does this mean for the future exploration of Mars? How can we seek out life in the solar system without harming it? Can robotic probes built on Earth be made clean enough to search for life on other planets without contaminating it? If we bring samples of alien life back to Earth, how do we prevent them from contaminating Earth’s biosphere? “Planetary protection” is the prevention of “cross contamination.” That is, preventing life from getting from one planet to another and causing harm. It’s an important factor in space exploration that the public is barely aware of, but one that NASA spends a lot of time working on.