First finding for Mars Odyssey

Mars Odyssey will survey the Red Planet

By BBC News Online science editor Dr David Whitehouse

The Mars Odyssey (MO) spacecraft has made its first significant discovery: it has detected large deposits of hydrogen - possibly water - near the Red Planet's poles.

Reporting MO's preliminary observations, scientists said the first pass by the probe's neutron spectrometer had revealed evidence of the element in soil at high latitudes.

"It is big," Bill Feldman, of Los Alamos National Laboratory, said of the strength of the signal picked up by Odyssey.

The results indicate large amounts of hydrogen on the surface, a likely sign of water-ice. The observations "are precisely what you would expect for a very hydrogen-rich environment", Feldman said.

Water, water, everywhere?

American space agency (Nasa) scientists said they were excited by the initial indications of hydrogen deposits, describing the readings sent back as clearer, more definite and much earlier than had been expected.

MO's image of Mars's south pole icecap

"We were expecting that it would take many orbits to determine the presence of hydrogen," said Stephen Saunders, a MO scientist. "But we saw it the very first time."

Scientists already know that water exists on Mars; it is frozen in the polar icecaps and exists as vapour in thin clouds.

There is also good evidence that water flowed on the planet's surface in the recent past, carving out deep channels and canyons.

Mapping mission

Significant water-ice deposits easily accessible from the surface would make it much more likely that life existed at some stage on Mars.

The MO is currently tightening its orbit around the Red Planet for a mapping mission that will get underway in January. It will use a battery of instruments to survey the planet's surface.

As well as the neutron spectrometer, its gamma-ray spectrometer will chart the chemical composition of the surface. Its infrared camera will peer at areas on the night side of Mars.

"We think it will be a very exciting winter and spring," James Garvin, a Nasa scientist, told a meeting of the American Geophysical Union in San Francisco.