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PASADENA — A NASA spacecraft will start peeling back the dry and dusty rust-red surface of Mars this month to reveal 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. 

Far more extensive amounts of water, even massive glaciers, could emerge from behind the dusty veil that cloaks the Red Planet, once the 2001 Mars Odyssey begins its 917-day science mission on or around Feb. 20. 

“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 $300 million National Aeronautics and Space Administration mission. 

The possibility charges scientists because it would support theories that the planet was once — and may still be — a wet world hospitable to life. On Earth, life is found wherever there is water, nutrients and a source of energy; the same rule may hold true elsewhere in the solar system. 

Today, 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 was lost to 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. 

Rather than dig into Mars, Odyssey will scout from afar, as the satellite orbits the planet at an average distance of about 250 miles. 

Using its thermal emission imaging system and a combination gamma ray spectrometer and neutron detector, the robotic probe will peer down on — and into — Mars. A third instrument, designed to monitor the radiation environment, has malfunctioned. 

As it orbits Mars every two hours, the spacecraft will use its instruments to map the distribution of chemicals and minerals in the top three feet or so of the surface of the planet. Among the 20 elements it 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. 

The frozen water is most likely mixed with dirt to form a permafrost similar to that found in the Alaskan tundra. On Mars, the deposits are probably scattered near the poles, in cold regions that receive less sunlight than those closer to the equator. Odyssey should determine how close to the equator those deposits extend. 

“We suspect, and I think we’ll find out very soon an answer, that there are lots of places where there is water ice frozen in the soil,” said Jeff Plaut, the mission’s deputy project scientist at the Jet Propulsion Laboratory. Tracking down where the water has gone remains a key goal of NASA’s Mars program.