The Phoenix probe may have achieved its objective of finding ice in the Martian polar region.

Phoenix has been digging up the soil and heating it in an attempt to find water vapour.

Nasa has now reported that white patches of ground exposed by the digging are almost certainly frozen water.

"It must be ice," said Phoenix principal investigator Peter Smith of the University of Arizona.

"These little clumps completely disappearing over the course of a few days is perfect evidence that it is ice. There had been some question whether the bright material was salt. Salt cannot do that."

The white chunks were originally exposed during the first dig by the probe but, when the team checked back four days later, they were gone.

Now the probe has discovered a hard layer in another trench at the same level of the particles believed to be ice.

Nasa Mission Control has also announced that it is beaming a software update to the probe so that it can store scientific data in its internal Flash memory.

Fears of a memory corruption led the team to beam back each day's data for fear that it might be overwritten by file maintenance data.

"We now understand what happened, and we can fix it with a software patch," said Phoenix project manager Barry Goldstein of Nasa's Jet Propulsion Laboratory in Pasadena.

"Our three-month schedule has 30 days of margin for contingencies like this, and we have used only one contingency day out of 24 sols. The mission is well ahead of schedule. We are making excellent progress toward full mission success. "