Water ice on Mars? What could that mean?

Yesterday, the mars Phonenix lander twittered (twitter.com/marsphoenix) that it had found ice, water ice on mars. There were some substance on the martian surface which sublimated leaving no traces, salt deposits does not do that, so scientists speculate that to be ice.

Why is this an exciting discovery? The presence of water on a planet, is a basic necessity for life to evolve, especially life similar to what we see on earth.

Scientists have long speculated, and there have been numerous unconfirmed details on martian surface which indicate to the presence of water, or atleast water existed long time back. Now finally they seem to have some form of evidence, further exploration by phoenix lander should confirm this historical finding. Also this leads to a much bigger question, is there life on mars now?

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Update:

Report from NASA Press conference June 20

- NASA Scientists say they are sure that the substance is water ice

- The phoenix lander mission was specifically sent to confirm that water ice existed on mars

- Ice/ice sheet is 2 inches deep below the dirt/sand

- The mission does not specifically look for life itself

- Could the white stuff be solid CO2 (dry ice)? No, it would turn to gas much quicker

- Is the white stuff any salt? No, would take a long time to disappear, if it indeed is salt and disappeared so fast then there is plenty of water to aid it

- The soil is clumpy and sticky why? we don't know yet

- The next task would be to test the ice for presence of minerals (food for life)

Disappearing Ice - NASA Press release:

Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University