For more than a decade, robotic probes sent to Mars have been searching for signs of past water, believed to be one of the key ingredients for life.
Now, NASA opens a new chapter in the search for extraterrestrial life with an ambitious mission to find life's habitats, and possibly even organics, on Mars.
"I'd be surprised if we landed on the surface (of Mars) and didn't find something that looked like it could have been a formerly habitable environment," said California Institute of Technology planetary scientist John Grotzinger, lead researcher for NASA's Mars Science Laboratory.
But what scientists really want to find is organic carbon -- molecules containing carbon that are derived from organic processes -- if indeed any has been preserved in the harsh Martian environment.
"It's a long shot, but we're going to try," Grotzinger told reporters during a pre-launch press conference.
It's been 35 years since NASA went looking for organics on Mars. Scientists didn't think the Viking lander twins, which touched down in 1976, found evidence of biological activity, though the results of one key experiment have been mired in controversy.
Mars Science Lab, nicknamed Curiosity, isn't a life-detection mission like Viking. Rather, it is intended to chemically analyze the landing site known as Gale Crater for habitats that could have supported life, or possibly still can.
Curiosity follows three previous rovers -- Pathfinder, Spirit and Opportunity -- the lander Phoenix, and a fleet of orbiting probes that have focused on looking for signs of past water. The previous missions returned overwhelming evidence that Mars was once a warmer and wetter place and hints that the planet once sported an ocean, rivers and other bodies of water on its surface.
The question now is whether the water existed long enough for life to evolve and if there were other ingredients necessary for life, namely organic compounds, which are the building blocks for life on Earth.
"One of the ingredients of life is water. We're now looking to see if we can find other conditions that are necessary for life by defining habitability or what does it take in the environment to support life," said Mary Voytek, director of NASA's astrobiology program.
The $2.5-billion rover is scheduled for launch at 10:02 a.m. EST Saturday from Cape Canaveral Air Force Station in Florida.
Its 60-million mile journey is expected to end in August 2012, with a touchdown inside the 96-mile wide Gale Crater. The site features a three-mile-high mountain of sediment that will be the focus of Curiosity's studies for at least two years.