In reality, it might not be Mars attacking us — but the other way around. In the next five years, we’re going to see new Mars-bound missions stoking dreams of space colonization. But NASA’s Office of Planetary Protection is increasingly worried by our Mars obsession. Experts say it’s likely there are very small organisms living on Mars. By sending robots or even people to the Red Planet, we could risk disrupting the evolution of an entire planet’s ecosystem — or wiping out terrestrial life with an alien contagion.