Pasadena, Calif. ? A NASA spacecraft will start examining the contents of the dry, dusty surface of Mars this week, searching for what scientists expect are vast, hidden stores of water.

Scientists already know there is water on Mars in ice that caps the north pole, frost seen at high latitudes and wispy clouds crowding the planet’s highest peaks.

	mars.jpl.nasa.gov/odyssey

Evidence of far more extensive amounts of water, even buried glaciers, could be found during the 2001 Mars Odyssey’s 917-day science mission that begins this week.

“You have a vast region that is perhaps just loaded with water,” said William Feldman of the Los Alamos National Laboratory, a scientist on the National Aeronautics and Space Administration’s $300 million Odyssey project.

The possibility excites scientists because it would support theories that the planet was once and may still be wet enough to be hospitable to life. On Earth, life is found wherever there is water, nutrients and a source of energy.

Mars abounds with evidence that torrents of water once flowed across its surface, carving channels, flooding plains and weeping from steep crater walls.

Whether that water remains locked within the planet or evaporated into space remains a mystery. Scientists believe Odyssey, and its ability to sniff out the hydrogen bound to oxygen that forms water, can provide an answer.

“That would make it very exciting, that there are still gobs and gobs of water there,” said William Boynton of the University of Arizona’s Lunar and Planetary Laboratory, another Odyssey scientist.

Locating water is a key goal of NASA’s Mars program, which includes plans for advanced robotic rovers that will land and dig into the surface.

Maps produced by Odyssey will guide those rovers to spots that appear rich in water today or that were soaked in the past.

Odyssey will also hunt for concentrations of chlorine, which would indicate locations where sodium chloride salt was deposited by standing water.

Odyssey entered orbit around Mars on Oct. 23. Since then, scientists have guided the craft through a series of maneuvers to shape its orbit into a circle with an average altitude of about 250 miles above the planet’s surface.

From that height, the robotic probe’s instruments a thermal emission imaging system and a combination gamma ray spectrometer and neutron detector will map the distribution of chemicals in the top three feet or so of the Martian soil. A third instrument, designed to monitor radiation, has malfunctioned.

Among the 20 elements the probe can detect is hydrogen, which indicates the likely presence of water.

“As long as it’s within a meter of the surface we are going to see it,” Boynton said.

Any water is most likely ice mixed with dirt to form a permafrost, similar to that found in the Alaskan tundra.