NASA MAVEN launch today: Another US Robotic explorer heading to Mars

This photo provided by NASA shows a full moon rising behind the United Launch Alliance Atlas V rocket with NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft onboard at the Cape Canaveral Air Force Station Space Launch Complex 41, Sunday, Nov. 17, 2013, Cape Canaveral, Florida. 

NASA's next Mars-bound spacecraft, the Mars Atmosphere and Volatile Evolution, or MAVEN, is the first spacecraft devoted to exploring and understanding the Martian upper atmosphere. 

AP Photo/NASA, Bill Ingalls

NASA's newest Martian explorer is on its launch pad in Florida, ready to soar.

The Maven spacecraft was scheduled to blast off aboard an unmanned Atlas V rocket Monday afternoon.

NASA is sending Maven to Mars to study its upper atmosphere. Scientists want to know why Mars went from being warm and wet during its first billion years, to the cold and dry place it is today.

The early Martian atmosphere was thick enough to hold water and possibly support microbial life. But much of that atmosphere may have been lost to space, eroded by the sun.

"Something clearly happened," the University of Colorado's Bruce Jakosky, the principal Maven scientist, said on the eve of Maven's flight.

"What we want to do is to understand what are the reasons for that change in the climate."

Maven—bearing eight science instruments—will take 10 months to reach Mars, entering into orbit around the red planet in September 2014. The mission costs $671 million.

A question underlying all of NASA's 21 Mars missions to date is whether life could have started on what now seems to be a barren world.