Mars Rising

Scientists explore the obstacles to getting a manned mission to Mars; the round-trip voyage to the Red Planet will take over two years and pose many physical and mental challenges.

Engineers tackle problems that they have just one opportunity to get right; the spacecraft set to take a crew to Mars is assembled -- in space.

A voyage to Mars could be punishing on the human body, which must be protected, as zero gravity depletes muscle and bone mass; cosmic radiation can cause brain damage and cancer.

The astronauts selected for the first mission to Mars must possess more skills than space explorers of the past.

The last six minutes of the flight to Mars -- entering the planet's orbit and the journey to its surface -- pose the greatest danger for the astronauts.

Scientists comb Earth's most barren places to seek bacteria, amino acids or carbonates that could offer clues to life on Mars, but Mars may have its own independently created lifeforms that are deadly to humans.