"A fundamental question for this mission is whether Mars could have supported a habitable environment," Michael Meyer, lead scientist for NASA's Mars Exploration Program said. "From what we know now, the answer is yes."

At a televised press conference, the NASA team said this is the first definitive proof a life-supporting environment had existed beyond Earth.

"There are places we've suggested could be habitable, but we haven't measured there," said Dave Blake, principal investigator for Curiosity's Chemistry and Mineralogy investigation.

Curiosity, a six-wheeled robot with 10 scientific instruments on board, is the most sophisticated vehicle ever sent to another planet.

The sample was drilled from sedimentary bedrock in an area which previous research had shown to be an ancient river system or lake bed.

It was found to contain clay minerals, sulfate minerals and other chemicals.

Based on the analysis of those chemicals, researchers were able to determine that the water in which the rocks were formed was of a relatively neutral pH — not overly salty, acidic, or oxidizing.

"We have found a habitable environment that is so benign and supportive of life, that probably if this water was around and you had been there, you would have been able to drink it," said John Grotzinger, a Curiosity project scientist from the California Institute of Technology.

Speaking at the same press conference, one of NASA's top officials John Grunsfeld said the discovery makes him "feel giddy."

He said the new data helps add to the picture of what the red planet may have looked in a previous era, with a possible freshwater lake and a snow-capped Mount Sharp.

But it wouldn't have looked like that any time recently, the researchers cautioned.

Although it is hard to confirm an exact date, it was probably at least three billion years ago, said Grotzinger.

Researchers also noted that future rock samples will be needed to confirm these results, because it is possible that residual carbon on the drill affected the analysis.

But "the instrument is working beautifully," enthused Paul Mahaffy, principal investigator for Curiosity's Sample Analysis at Mars investigation.

The team is already planning out where and when to take the next rock samples, as well as planning out the rover's route to nearby Mount Sharp, where mineral analysis should help with dating calculations.

The $2.5 billion nuclear-powered Curiosity has been exploring the planet's surface since its dramatic landing on August 6, for an anticipated two-year mission.

Scientists do not expect Curiosity to find aliens or living creatures — and indeed, they said Tuesday, the rover does not have the capability to identify microbial life or fossils, even if they were present today.

But the analysis of soil and rocks is aimed at finding evidence Mars may have supported life in the past.