Multimillion-mile Mars journey begins

LESTER HOLT, anchor: The folks at NASA are calling it the monster truck of Mars . And tonight the world's biggest extraterrestrial explorer is on its way to the red planet . For NASA , this new mission in search of life carries high hopes and high risks. NBC 's Tom Costello has our report.

Offscreen Voice: Five, four, three, two, one...

TOM COSTELLO reporting: With the Saturn Five liftoff at the Kennedy Space Center , NASA has launched its most sophisticated and ambitious mission to Mars yet. Just traveling the 154 million miles to the red planet will take more than eight months. Then next August, a high-risk landing as a supersonic parachute slows the science lab 's descent to Mars . Sixty feet above the planet, a sky crane will gently lower the rover named Curiosity onto the Martian surface, leaving Curiosity on its own to begin looking for signs of life, past or present.

Ms. PAMELA CONRAD (Astrobiologist): Do we anticipate that we'll learn a whole lot about Mars ? Absolutely. Do we know what specifically that will be? No clue.

COSTELLO: Curiosity is a six-wheeled rover standing more than six feet tall, able to drive long distances under a hot Martian sun, analyzing rock and soil samples and then transmitting those findings back to Earth . NASA has carefully selected the landing zone on Mars in the Gale Crater , where a huge mountain rises right out of the crater floor. Scientists believe they see layers of sedimentary deposit here that they hope will help them understand more about Mars ' history, but also what happened to the lakes and rivers.

Mr. BRIAN HYNEK: This is Gale Crater .

COSTELLO: Brian Hynek is a planetary science professor and Mars expert at the University of Colorado . The evidence he says now seems clear that Mars once had a very warm and wet environment.

Mr. HYNEK: Microbial life could've persisted for hundreds of millions of years on ancient Mars and perhaps even today.

COSTELLO: And that possibility poses a big problem. NASA has gone to great lengths to ensure Curiosity doesn't carry any Earth germs that could contaminate life on Mars . High resolution cameras have already detected what appear to be large ice sheets buried under the Martian surface. Curiosity 's mission, to determine whether life is or ever was buried there, too. Tom Costello, NBC News, Washington.