New Mars Orbiter's Strategy: 'Follow the Water'

· A high-resolution camera, the most powerful ever built for imaging another planet, will look at landforms such as gullies, dunes and boulders as small as three feet in diameter. It will help scientists determine whether surface channels were cut by wind, liquid water, glacial ice or lava.

· An imaging spectrometer, which can differentiate among 544 wavelengths of energy reflected from the ground, will be able to identify many minerals on the ground, each of which has its own reflective "fingerprint." Scientists will look especially for minerals typically formed by water-related processes, including clays, carbonates and salts, whose presence could indicate that ponds or hot springs were once there.

· A context camera will take panoramic black-and-white images of the planet's surface in 19-mile swaths to identify features worthy of closer inspection by other instruments and to answer questions about how the Martian surface has evolved over geologic time.

· A Mars color imager, whose extremely wide-angle lens can shoot pictures stretching from one horizon to the other, will produce daily weather maps of the entire planet and track seasonal changes on the ground and in the Martian atmosphere.

· A Mars "climate sounder" will use a pair of infrared telescopes to track how water vapor, ice and dust in the atmosphere move and vary from day to night and through the seasons. Instead of simply looking straight down, as previous Mars orbiters have, it also will look sideways to the Martian horizon, to analyze three-mile-thick layers of the atmosphere from ground level up to an altitude of 50 miles. Among other things, that layer-cake view will allow a detailed analysis of how gases such as carbon dioxide are exchanged between the atmosphere and the planet's ice caps, providing data crucial to understanding climate on both Mars and Earth.

· A subsurface radar device will beam radio waves as deep as half a mile beneath the Martian surface, then analyze the reflected energy to distinguish layers of rock, water and ice. With its ability to resolve layers of material just 33 feet thick, it may finally answer the question of whether the surface ice detected by previous spacecraft is just the tip of a Martian iceberg.

Information from these instruments will be transmitted to an Earth-based network of giant receiving antennas in California, Spain and Australia at speeds 10 times what was possible in previous Mars missions. A total of at least 26 terabits of information is expected -- more than every other Mars mission combined.

Among the images that may turn up: A picture of the Mars Polar Lander, which lost contact with Earth as it tried to make a soft landing in 1999.

Any clues as to why that crash occurred -- an image revealing whether the parachute opened, for example -- could be useful, scientists said, especially because the design of the Phoenix Mars Scout lander, scheduled to launch in 2007, is closely derived from that of the ill-fated polar lander.