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In its first few days of science operations, the spacecraft detected evidence of abundant frozen water mixed in the top few feet of the powdery Martian soil. At a March 1 press conference, mission scientists reported that additional observations and analysis should allow them to determine the amount of water present around the pole.

Scientists are looking for evidence of water on Mars because water is considered a key ingredient for life.

There is evidence that Mars was much warmer and wetter in the distant past, boosting the chance that life could have evolved on the planet. Orbiting spacecraft have mapped large channels that look like they were carved by running water, as well as regions that look like ancient shorelines.

Although water is less common on Mars today, there’s growing evidence that the planet is not as dessicated as once thought. Mars Global Surveyor, which has orbited Mars since 1997, has found evidence that water in underground reservoirs periodically gushes to the surface even now, carving small gullies and channels.

Mars Odyssey began its science mission in late February after spending four months “surfing” through the planet’s upper atmosphere to refine its orbit. Within days of beginning its work, the craft’s gamma-ray spectrometer had detected evidence of abundant hydrogen around the south pole. The hydrogen most likely is in the form of water ice. The instrument also detected hydrogen around the north pole, though not as much as in the south, plus smaller pockets scattered around the planet.

The possible discovery of water ice around the south pole is particularly interesting because a group of European scientists has proposed that small black spots that pop into view around the pole in early spring are beds of blooming microorganisms.

Most scientists believe there is a chemical or physical cause for the spots, such as the evaporation and refreezing of carbon-dioxide ice. But András Horváth, Tibor Gánti, and Eörs Szathmáry of the Planetarium and Institute for Advanced Study in Budapest proposed a biological explanation. They say that microorganisms beneath the polar ice cap may “bloom” as the cap thins and retreats in early spring. They heat the ice around them, forming a thin layer of liquid water. When the ice covering disappears, the organisms dry out.

Not all the recent news about possible Martian water and life is favorable, though. A team led by Kenneth L. Tanaka of the U.S. Geological Survey reported that some Martian channels probably were carved by flows of frozen carbon dioxide, not water. In the journal Geophysical Research Letters, the scientists wrote that several channels in the Hellas Basin probably formed when frozen carbon dioxide, warmed by molten rock, erupted to the surface and flowed downhill, like glaciers. Most scientists believe that water carved such channels, but not all agree. Future landers and rovers may settle the issue by measuring the chemical composition of rocks and soil in the area to see if they were altered by exposure to water.