A manned mission to the Red Planet could turn out to be the 21st century's greatest adventure. A journey to Mars would be the fulfillment of centuries-old dreams, as well as a huge shot in the arm for NASA, or any other country's space program. And there's a chance that the mission could uncover some form of microbial life, which would rank as one of the greatest scientific discoveries of all time. Okay, there are still a few wrinkles left to iron out. A one-way trip to Mars would take about seven months, exposing astronauts to potentially dangerous levels of cosmic radiation, and bringing enough food, water, and fuel for a mission lasting well over a year is a boggling logistical challenge. But it wasn't all that long ago that the best minds in the world thought a journey to the moon was utterly impossible.