As the world wishes NASA's Opportunity rover a happy 10th anniversary, here comes a starling announcement that the Mars rover has found concrete evidence about presence of fresh water on the red planet.

Ten years ago, Jan 24, 2004, the Opportunity rover landed on a flat plain on Mars and rolled into an impact crater scientists did not even know existed.

Celebrating the rover's 10th anniversary Jan 23, Ray Arvidson, deputy principal investigator of the dual-rover mission at NASA, said cold and dry Mars once had exploding volcanoes with hydrothermal vents, steam-charged vents, rivers, dendritic streams and lakes.

"The older you look, the better it gets in terms of warm and wet," Arvidson told the audience at Washington University in St Louis.

However dirty it may be after 10 years, Opportunity has found evidence of conditions that would support life in the planet's past, said Arvidson and reported in the current issue of Science magazine.

"We're exploring Mars to better understand Earth. On Mars, we can learn about geological processes and environmental processes - maybe habitability, maybe life, that remains to be seen - for a period of time that's lost on Earth," Arvidson added.
The farther back we look in the rock record, the better the chemical conditions for life, he told the gathering.

In August 2012, another NASA rover called Curiosity landed on Mars to understand if there were ingredients essential for life. The field geologist has sent back answers that indicates red planet was once brimming with life.

"We lost Spirit, Opportunity's twin, back in 2010," Arvidson said, adding that he is happy at Opportunity's survival instincts.

They were supposed to drive maybe a thousand metres, and Opportunity is now about to break 40,000 metres, he said.