The puzzle of planetary protection

The recent announcement by NASA confirming the presence of liquid water on Mars pulls planetary protection into the spotlight and is causing some serious head-scratching in the scientific community. On the one hand, having existing liquid water on the Red Planet is a cause for wonder, excitement, and a strong desire to investigate it in a great deal more depth to look for the possibility of life. On the other hand, there is the dilemma of protecting a potential biosphere from contamination from