Has there ever been life on another planet? It's the big picture question scientists have been grappling with for centuries - and the Mars rover Curiosity might be about to deliver us an answer.

Dramatic off-the-cuff remarks from NASA’s John Grotzinger - the top scientist investigating the rover’s findings - have stirred speculation the adventurous hi-tech robot has made a big discovery.



“This data is going to be one for the history books,” Grotzinger told a National Public Radio reporter. “It’s looking really good.”



Like a paleontologist looking for fossilised dinosaur bones, the robot is sifting through the red dirt of the planet’s Gale Crater hunting for a substance that may indicate life once existed on Mars – methane. Methane is an organic compound, which means it’s a building block for life.



Curiosity is equipped with highly sophisticated in-built chemical analysis laboratory to detect this substance, and others. And it’s the results beamed from this lab to Earth that have got Grotzinger, the chief investigator on the rover project, excited, leaving space experts to speculate they have found evidence for life.



“I’d say I’m cautiously optimistic,” says space expert and Australasian Science Magazine writer, David Reneke. It’s significant that someone in the know, the chief investigator on the Curiosity mission, is trumpeting history-making success, Reneke told News.com.au.



But NASA will be taking its time to confirm what they’ve actually found.

There’s good reason for the US space agency to be cautious.



Scientists have been embarrassed before when they’ve thought they’ve discovered life on the red planet, Reneke says, and “it just turns out to be different coloured dirt.”



“I don’t want different coloured dirt,” he says. “I want someone to stick their arm out and say, ‘g’day mate’”.



Reneke says even the first rover we sent to Mars, the Viking probe, thought it had found evidence of organic material.



And in 1996, NASA scientists thought they had discovered evidence of organic material in a 2 kilogram Martian meteorite, ALH84001, which had crashed into the Allan Hills region of Antarctica.



Later that year, US president Bill Clinton famously issued a statement hailing the possibility of life on Mars.



“Today, rock 84001 speaks to us across all those billions of years and millions of mile,” Clinton said, according to a NASA transcript. “It speaks of the possibility of life.



“If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered.



“Its implications are as far-reaching and awe-inspiring as can be imagined.”



And that’s where it stayed: in our imaginations.



NASA later retreated from claims the rock indicated there was life on Mars and the controversy continues to this day.



The Curiosity rover, which landed on Mars in August, is the most hi-tech machine humans have ever placed on another planet. It has stereoscopic vision (meaning it can see like a human), it’s armed with a powerful drill, more powerful than anything you’d see on the shelves at Bunnings and it has showcased its perky personality on the social media website Twitter.



The rover has made some concrete findings. Earlier this month, NASA announced the Rover had confirmed human astronauts would be able to survive the radiation levels in Mars’s atmosphere.