If humans ever go to Mars, the worst of our impulses will accompany us there. The Red Planet will not rid us of murder, violence, and blackmail. There will be kidnapping, extortion, and burglary. Given time, we will even see bank heists. For generations, people have imagined life on the Martian surface in extraordinary detail, from how drinking water will be purified to how fresh food will be grown, but there is another question that remains unanswered: How will Mars be policed?