March 31, 2008 —NASA's Mars Odyssey orbiter has found evidence of salt deposits that could mean water was once abundant on the Red Plant and that life existed there, too.
A team led by Mikki Osterloo of the University of Hawaii found approximately 200 places on southern Mars that show spectral characteristics consistent with chloride minerals. Chloride is part of many types of salt, such as sodium chloride or table salt. The sites range from about 0.4 square mile to 25 times that size.
"They could come from groundwater reaching the surface in low spots," Osterloo said. "The water would evaporate and leave mineral deposits, which build up over years. The sites are disconnected, so they are unlikely to be the remnants of a global ocean."
Scientists used Odyssey's Thermal Emission Imaging System to take images in a range of visible light and infrared wavelengths. Thermal infrared wavelengths are useful for identifying different mineral and rock types on the Martian surface. Osterloo found the sites by looking through thousands of images processed to reveal, in false colors, compositional differences on the Martian surface.
Plotted on a Mars map, the chloride sites appear only in the southern highlands, the most ancient rocks on Mars. Osterloo and seven co-authors reported the findings this month in the journal Science.
"Many of the deposits lie in basins with channels leading into them," said Philip Christensen, co-author and principal investigator for the camera at Arizona State University. "This is the kind of feature, like salt-pan deposits on Earth, that's consistent with water flowing in over a long time."
Scientists think the salt deposits formed approximately 3.5 to 3.9 billion years ago. Several lines of evidence suggest Mars then had intermittent periods with substantially wetter and warmer conditions than today's dry, frigid climate.
"By their nature, salt deposits point to a lot of water, which potentially could remain standing in pools as it evaporates," said Christensen. "That's crucial. For life, it's all about a habitat that endures for some time."
Whether life ever has existed on Mars is the biggest scientific question driving Mars research. "This discovery demonstrates the continuing value of the Odyssey science mission, now entering its seventh year. The more we look at Mars, the more fascinating a place it becomes," said Jeffrey Plaut, Odyssey project scientist at NASA's Jet Propulsion Laboratory.
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BRIGHT BLUE marks a deposit of chloride (salt) minerals in the southern highlands of Mars in this THEMIS false-color image that highlights mineral composition differences. Using THEMIS, researchers have found more than 200 such features. These deposits typically lie within topographic depressions and suggest that Mars was much wetter long ago. The black rectangle
shows the outline of a close-up view.
Credit: NASA/JPL/Arizona State University/University of Hawaii
This image provides higher-resolution views of a site where another observation (PIA10247) indicates the presence of chloride salt deposits. The High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter took this image, that show the chloride mineral deposit bright in tone, like salt pans on Earth. Inset boxes show two areas in greater detail, revealing cracks that formed as the salt deposit dried. Scale bars are 1 kilometer (six-tenths of a mile) and 100 meters (110 yards). Source: NASA/JPL-Caltech/University of Arizona/Arizona State University/University of Hawaii
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