NASA's Mars Odyssey
orbiter has found evidence of salt deposits. These deposits point to places
where water once was abundant and where evidence might exist of possible
Martian life from the Red Planet's past.
A team led by Mikki Osterloo of the University of Hawaii, Honolulu,
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 half of a 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, a camera
designed and operated by Arizona State University, Tempe, 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
report the findings in this week's issue of 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.
Scientists looking for evidence of past life on Mars have focused
mainly on a handful of places that show evidence of clay or sulfate
minerals. Clays indicate weathering by water, and sulfates may have formed
by water evaporation. The new research, however, suggests an alternative
mineral target to explore for biological remains.
"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. On Earth, salt is good at preserving
organic material. Bacteria have been revived in the laboratory after being
preserved in salt deposits for millions of years.
"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, Pasadena, Calif.
"This is a wonderful and scientifically exciting result obtained from a
relatively low cost NASA Mars orbiter mission which still has years of life
left," said Alan Stern, associate administrator for NASA's Science Mission
Directorate in Washington. "Hold on to your hats, more exciting results
from Mars are sure to be coming."
Source: NASA
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