The research team, which works with Mars Phoenix Mars Lander, anticipates even bigger discoveries from the robotic mission in the weeks ahead, after it has confirmed that the hard bright material discovered is really water ice and not some other substance.

Phoenix Principal Investigator Peter Smith of the University of Arizona, Tucson has confirmed that key evidence is that the big white chunks exposed by digging on June 15 and still present on June 16 had vaporized by June 19.

"The truth we're looking for is not just looking at ice. It is in finding out the minerals, chemicals and hopefully the organic materials associated with these discoveries," said Smith

The mission has the right instruments for analyzing soil and ice to determine whether the local environment just below the surface of far-northern Mars has ever been favorable for microbial life. Key factors are whether the water ever becomes available as a liquid and whether organic compounds are present that could provide chemical building blocks and energy for life.

Water is a key to four of the most critical questions about Mars: Has Mars ever had life? How should humans prepare for exploring Mars? What can Mars teach us about climate change? How do geological processes differ on Mars and on Earth? Water is a prerequisite for life, a potential resource for human explorers and a major agent of climate and geology. That’s why NASA has pursued a strategy of “follow the water” for investigating Mars. Orbiters and surface missions in recent years have provided many discoveries about the history and distribution of water on Mars-- such as minerals that formed in wet environments long ago and liquid flows that are still active today in hillside gullies.

Mark Lemmon of Texas A&M University, College Station, lead scientist for Phoenix's Surface Stereo Imager camera, explained that the disappearing chunks could not have been carbon-dioxide ice at the local temperatures because that material would not have been stable for even one day as a solid.

On a time scale of billions of years, ice near the surface where Phoenix will land might be the remnant of an ancient northern sea. Several types of evidence point to plentiful liquid water on ancient Mars, and the northern hemisphere is low and smooth compared to the southern hemisphere. Much of the water that could have remained liquid when ancient Mars had a thicker atmosphere may now be underground ice.

The disappearing chunks were in a trench to the northwest of the lander. A hard material, possibly more ice, but darker than the bright material in the first trench, has been detected in a second trench, to the northeast of the lander. Scientists plan next to have Phoenix collect and analyze surface soil from a third trench near the second one, and later to mechanically probe and sample the hard layer.

"We have in our ice-attack arsenal backhoeing, scraping and rasping, and we'll try all of these," said Ray Arvidson of Washington University in St. Louis, lead scientist for Phoenix's Robotic Arm.