Nasa has confirmed that it has "definitely" found water on Mars.

The space agency had already said that it was "fairly certain" that the ice samples it was analysing were made of water.

But the Phoenix probe has now managed to heat up a sample and the substance is definitely water.

"We have water," said William Boynton of the University of Arizona, lead scientist for the Thermal and Evolved-Gas Analyzer which has been studying soil samples.

"We have 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."

The sample was taken from a two-inch trench dug into the Martian surface. The knowledge that water is available on the planet would make a manned mission much more feasible.

Nasa has also announced that it is extending the mission time for the Phoenix probe for five weeks until the end of September.

"Phoenix is healthy and the projections for solar power look good, so we want to take full advantage of having this resource in one of the most interesting locations on Mars," said Michael Meyer, chief scientist for the Mars Exploration Program at Nasa Headquarters in Washington.