NASA scientists have said they had definitive proof that water exists on Mars after further tests on ice found on the planet in June.

'We have water,' said William Boynton, lead scientist for the Thermal and Evolved-Gas Analyzer instrument on the Phoenix Mars Lander .

'We've seen evidence for this water ice before in observations by the Mars Odyssey orbiter and in disappearing chunks observed by Phoenix last month, but this is the first time Martian water has been touched and tasted,' he said, referring to the craft's instruments.

NASA has also extended the mission of the Phoenix Mars Lander by five weeks, saying its work was moving beyond the search for water to exploring whether the red planet was ever capable of sustaining life.

'We are extending the mission through 30 September,' Michael Meyer, chief scientist for NASA's Mars exploration program, told a televised news conference.

The extension will add about €1.3m to the €269m cost of landing Phoenix on 25 May for what was a scheduled three-month mission, Mr Meyer said.

Phoenix is the latest NASA bid to discover whether water ever flowed on Mars and whether life, even in the form of mere microbes, exists or ever existed there.

Phoenix touched down in May on an ice sheet and samples of the ice were seen melting away in photographs taken by the lander's instruments in June.

Mr Boynton said that water was positively identified after the lander's robotic arm delivered a soil sample yesterday to an instrument that identifies vapours produced by heating.

Mission scientists said in June that Martian soil was more alkaline than expected and had traces of magnesium, sodium, potassium and other elements. They described the findings as a huge step forward.

Mr Meyer said the scientific proof of the existence of water meant that Phoenix could move from looking for water to seeing whether there were habitats for life.

'We are moving towards understanding whether there were or could be places on Mars that are habitable,' Mr Meyer said.