This false-color infrared image was taken by the camera system on the Mars Odyssey spacecraft over part of Ganges Chasma in Valles Marineris (approximately 13 degrees S, 318 degrees E). The infrared image has been draped over topography data obtained by Mars Global Surveyor. The color differences in this image show compositional variations in the rocks exposed in the wall and floor of Ganges (blue and purple) and in the dust and sand on the rim of the canyon (red and orange).

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By Robert Roy Britt
Senior Science Writer
posted: 10:30 am ET
14 March 2003

Ice and other substances


After a full year of collecting science data, the Mars Odyssey spacecraft is in excellent health and set for at least another year-and-a-half of observing, a NASA official said Thursday. Odyssey is also generating new mysteries that scientists hope the probe will solve during the remainder of its tenure in orbit around the Red Planet.

While lauding the spacecraft's accomplishments at a press conference, scientists discussed new images and data that fuel fresh questions about the planet's apparent watery and volcanic past.

In one image, Odyssey's full capabilities began to shine as several observations were compiled to generate a scientifically intriguing color mosaic of the Ganges Chasma in the colossal Valles Marineris.

The color differences in the image show compositional variations in exposed rocks in the wall and floor of the canyon. The colors reveal, to scientists, that the floor of Ganges is covered by basaltic lava and is rich in the mineral olivine, which shows up in layers that were once buried under three miles of material. Both substances suggest extensive lava flows in the past.

Because olivine is easily destroyed by water, its presence suggests the region has been dry for a long time.

"What this layer of olivine-rich basalt is doing there is a wonderful mystery," said Philip Christensen, an Arizona State University scientist who is the principal investigator of Odyssey's infrared imager, called THEMIS.

They canyon itself might have been carved by water, other studies have shown, but scientists have not reached agreement on how Mars got its deep scars.

In the same press conference, held at NASA's Jet Propulsion Laboratory, relatively solid but preliminary data was discussed revealing that Mars' radiation environment will be hazardous, but likely manageable, to astronauts who might travel there.

More water clues

Odyssey's chemical-sniffing gamma ray spectrometer, which has been finding more and more solid evidence for vast quantities of water ice on Mars, continues to generate new results. These, too, prove inexplicable for now.

The northern hemisphere of Mars contains too much water ice to be explained by conventional ideas of the Martian climate, said William Boynton, a University of Arizona researcher who manages Odyssey's gamma-ray instrument. Recent observations suggest soil in much of the north contains mostly ice with some dirt mixed in, not the other way around, he said.

"It's really a huge amount of ice," Boynton said.

Scientists had thought ice in the soil away from the permanently frozen polar caps seeped in from the atmosphere, diffusing into the pores of the soil. But Boynton said there seems to be more ice than the estimated 40 percent pore space in the soil could hold. Perhaps annual snowfalls once deposited the stuff, he said.

Odyssey does not detect water ice directly, but instead finds hydrogen, a constituent of water. Mars experts are convinced the hydrogen represents water ice.

Other chemicals

Boynton also unveiled the first global maps showing the distributions of the chemicals potassium and thorium. In those, he said, were hints about the composition of Mars and its climate history. Scientists had thought the chemical makeup of the older, southern highlands of the planet would be different from the younger terrain of the northern lowlands.

"We don't actually see that," Boynton said, adding to the list of fresh Martian puzzles.

He added that there were unexplained differences in levels of potassium and thorium at various spots that suggested water leaching in the past.

Boynton also showed a new map of iron distribution on Mars. Iron is behind the planet's reddish tint. Curiously, he said, locations richest in iron do not correspond to variations in color seen in visible-light photographs of Mars.

"It's going to be a hard job to unravel these differences."

But there is time. Odyssey's main mission is slated to last another year-and-a-half. NASA will review the mission's costs and effectiveness and might extend it. At least one person thinks the record is pretty convincing for an extension.

"In just one year, Mars Odyssey has fundamentally changed our understanding of the nature of the materials on and below the surface of Mars," said Jeffrey Plaut, Odyssey's project scientist at JPL.


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