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Scientists say water on Mars would have been 'pure enough to drink', as presence of oxygen and carbon prove conditions are ideal for life

New discoveries are the clearest indicator yet that life could once have existed on the red planet

The water that may once have flowed freely on the surface of Mars is likely to have been pure enough for humans to drink, Nasa scientists have revealed.

Samples of rocks heated to nearly 1100C revealed clay minerals which indicate that water once flowed freely in the ancient stream bed from which they were taken.

The revelations are the clearest indicator yet that life could once have existed on Mars, as flowing water is likely to have created conditions ideal for microbial life.

John Grotzinger, a lead scientist on the £1.7 billion Curiosity rover, said: “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”.

As well as clay, the heated rocks revealed elements of sulphur, nitrogen, hydrogen, oxygen, phosphorus and carbon – all key chemicals for sustaining life as we know it.

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

The Curiosity rover has been exploring an area in Mars’ Gale crater known as Yellowknife Bay, which is where the examined rocks were found.

Scientists believe the Bay to be at the end of an ancient river network but insist that, although the area is likely to have been habitable, there is still no indication it was actually inhabited.

Curiosity will continue to operate in the Yellowknife Bay area for the next few weeks, before it moves on to Gale crater’s central mound, Mount Sharp.

The purpose of Curiosity’s exhibition is not to find life itself, but to prove whether life could have existed at some point in the planet’s history.

As such, the discovery of material that indicates flowing water, as well as chemical elements key to the existence of life, mean the Curiosity mission is well on its way to success.

John Bridges, a member of the Curiosity team based at Leicester University said: “It's a remarkable achievement. We are starting to see results from MSL that already justify the mission…We'll take it one sol [a Martian day] at a time.”